Applied Thermodynamics

COURSE MATERIAL II Year B. Tech II- Semester MECHANICAL ENGINEERING APPLIED THERMODYNAMICS R18A0308 MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY DEPARTMENT OF MECHANICAL ENGINEERING (Autonomous Institution-UGC, Govt. of India) Secunderabad-500100, Telangana State, India. www.mrcet.ac.in MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) DEPARTMENT OF MECHANICAL ENGINEERING CONTENTS 1. Vision, Mission and Quality Policy 2. POs, PSOs & PEOs 3. Blooms Taxonomy 4. Course Syllabus 5. Course Outline. 6. Mapping of Course Objectives. 7. Unit wise course Material a. Objectives and Outcomes b. Detailed Notes c. Industry applications relevant to the concepts covered d. Tutorial Questions e. Question bank for Assignments: 05/Unit 8. Previous Question papers: 05 www.mrcet.ac.in MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) VISION ❖ To establish a pedestal for the integral innovation, team spirit, originality and competence in the students, expose them to face the global challenges and become technology leaders of Indian vision of modern society. MISSION ❖ To become a model institution in the fields of Engineering, Technology and Management. ❖ To impart holistic education to the students to render them as industry ready engineers. ❖ To ensure synchronization of MRCET ideologies with challenging demands of International Pioneering Organizations. QUALITY POLICY ❖ To implement best practices in Teaching and Learning process for both UG and PG courses meticulously. ❖ To provide state of art infrastructure and expertise to impart quality education. ❖ To groom the students to become intellectually creative and professionally competitive. ❖ To channelize the activities and tune them in heights of commitment and sincerity, the requisites to claim the never - ending ladder of SUCCESS year after year. For more information: www.mrcet.ac.in MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) www.mrcet.ac.in Department of Mechanical Engineering VISION To become an innovative knowledge center in mechanical engineering through state-ofthe-art teaching-learning and research practices, promoting creative thinking professionals. MISSION The Department of Mechanical Engineering is dedicated for transforming the students into highly competent Mechanical engineers to meet the needs of the industry, in a changing and challenging technical environment, by strongly focusing in the fundamentals of engineering sciences for achieving excellent results in their professional pursuits. Quality Policy  To pursuit global Standards of excellence in all our endeavors namely teaching, research and continuing education and to remain accountable in our core and support functions, through processes of self-evaluation and continuous improvement.  To create a midst of excellence for imparting state of art education, industryoriented training research in the field of technical education. MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) www.mrcet.ac.in Department of Mechanical Engineering PROGRAM OUTCOMES Engineering Graduates will be able to: 1. Engineering knowledge: Apply the knowledge of mathematics, science, engineering fundamentals, and an engineering specialization to the solution of complex engineering problems. 2. Problem analysis: Identify, formulate, review research literature, and analyze complex engineering problems reaching substantiated conclusions using first principles of mathematics, natural sciences, and engineering sciences. 3. Design/development of solutions: Design solutions for complex engineering problems and design system components or processes that meet the specified needs with appropriate consideration for the public health and safety, and the cultural, societal, and environmental considerations. 4. Conduct investigations of complex problems: Use research-based knowledge and research methods including design of experiments, analysis and interpretation of data, and synthesis of the information to provide valid conclusions. 5. Modern tool usage: Create, select, and apply appropriate techniques, resources, and modern engineering and IT tools including prediction and modeling to complex engineering activities with an understanding of the limitations. 6. The engineer and society: Apply reasoning informed by the contextual knowledge to assess societal, health, safety, legal and cultural issues and the consequent responsibilities relevant to the professional engineering practice. 7. Environment and sustainability: Understand the impact of the professional engineering solutions in societal and environmental contexts, and demonstrate the knowledge of, and need for sustainable development. 8. Ethics: Apply ethical principles and commit to professional ethics and responsibilities and norms of the engineering practice. 9. Individual and teamwork: Function effectively as an individual, and as a member or leader in diverse teams, and in multidisciplinary settings. 10. Communication: Communicate effectively on complex engineering activities with the engineering community and with society at large, such as, being able to comprehend and write effective reports and design documentation, make effective presentations, and give and receive clear instructions. 11. Project management and finance: Demonstrate knowledge and understanding of the engineering and management principles and apply these to one’s own work, as a member and leader in a team, to manage projects and in multidisciplinary environments. MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) www.mrcet.ac.in Department of Mechanical Engineering 12. Life-long learning: Recognize the need for and have the preparation and ability to engage in independent and life-long learning in the broadest context of technological change. PROGRAM SPECIFIC OUTCOMES (PSOs) PSO1 Ability to analyze, design and develop Mechanical systems to solve the Engineering problems by integrating thermal, design and manufacturing Domains. PSO2 Ability to succeed in competitive examinations or to pursue higher studies or research. PSO3 Ability to apply the learned Mechanical Engineering knowledge for the Development of society and self. Program Educational Objectives (PEOs) The Program Educational Objectives of the program offered by the department are broadly listed below: PEO1: PREPARATION To provide sound foundation in mathematical, scientific and engineering fundamentals necessary to analyze, formulate and solve engineering problems. PEO2: CORE COMPETANCE To provide thorough knowledge in Mechanical Engineering subjects including theoretical knowledge and practical training for preparing physical models pertaining to Thermodynamics, Hydraulics, Heat and Mass Transfer, Dynamics of Machinery, Jet Propulsion, Automobile Engineering, Element Analysis, Production Technology, Mechatronics etc. PEO3: INVENTION, INNOVATION AND CREATIVITY To make the students to design, experiment, analyze, interpret in the core field with the help of other inter disciplinary concepts wherever applicable. PEO4: CAREER DEVELOPMENT To inculcate the habit of lifelong learning for career development through successful completion of advanced degrees, professional development courses, industrial training etc. MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) www.mrcet.ac.in Department of Mechanical Engineering PEO5: PROFESSIONALISM To impart technical knowledge, ethical values for professional development of the student to solve complex problems and to work in multi-disciplinary ambience, whose solutions lead to significant societal benefits. MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) www.mrcet.ac.in Department of Mechanical Engineering Blooms Taxonomy Bloom’s Taxonomy is a classification of the different objectives and skills that educators set for their students (learning objectives). The terminology has been updated to include the following six levels of learning. These 6 levels can be used to structure the learning objectives, lessons, and assessments of a course. 1. Remembering: Retrieving, recognizing, and recalling relevant knowledge from long‐ term memory. 2. Understanding: Constructing meaning from oral, written, and graphic messages through interpreting, exemplifying, classifying, summarizing, inferring, comparing, and explaining. 3. Applying: Carrying out or using a procedure for executing or implementing. 4. Analyzing: Breaking material into constituent parts, determining how the parts relate to one another and to an overall structure or purpose through differentiating, organizing, and attributing. 5. Evaluating: Making judgments based on criteria and standard through checking and critiquing. 6. Creating: Putting elements together to form a coherent or functional whole; reorganizing elements into a new pattern or structure through generating, planning, or producing. MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) www.mrcet.ac.in Department of Mechanical Engineering B. Tech (MECH) R-18 MALLAREDDY COLLEGE OF ENGINEERING & TECHNOLOGY II Year B. Tech, ME-II Sem L P C 3 0 3 (R18A0308) APPLIED THERMODYNAMICS Course Objectives:  Applications and the principles of thermodynamics to components and systems.  The purpose of this course is to enable of how thermodynamic govern the behavior of systems.  Students h a v e knowledge of methods of analysis and design of complicated thermodynamic systems.  Acquires knowledge about thermodynamic analysis for steam nozzles.  Acquires knowledge on condensers and steam turbines UNIT-I Basic Concepts: Rankine cycle - Schematiclayout, Thermodynamic Analysis, Concept of Mean Temperature of Heat addition, Methods to improve cycle performance - Regeneration & reheating Boilers: Classification - Working principles with sketches including H.P. Boilers - Mountings and Accessories - Working principle. UNIT-II Steam Nozzles: Function of nozzle - Applications and Types- Flow through nozzlesThermodynamic analysis. Steam Condensers: Requirements of steam condensing plant - Classification of condensers - Working principle of different types. UNIT-III Steam Turbines: Classification - Impulse turbine; Mechanical details - Velocity diagram Effect of friction - Power developed, Axial thrust, Blade or diagram efficiency - Condition for maximum efficiency. Reaction Turbine: Mechanical details - Principle of operation, Thermodynamic analysis of a stage, Degree of reaction - Velocity diagram - Parson's reaction turbine - Condition for maximum efficiency. UNIT-IV Gas Turbines: Simple gas turbine plant - Ideal cycle, essential components - Parameters of performance - Actual cycle - Regeneration, Inter cooling and Reheating - Closed and Semi closed cycles - Merits and Demerits. MRCET CAMPUS B. Tech (MECH) R-18 UNIT-V Jet Propulsion: Principle of Operation - Classification of jet propulsive engines - Working Principles with schematic diagrams and representation on T-S diagram- Thrust, Thrust Power and Propulsion Efficiency - Turbo jet engines - Needs and Demands met by Turbo jet Schematic Diagram, Thermodynamic Cycle, Performance Evaluation Thrust Augmentation Methods. Rockets: Application - Working Principle - Classification - Propellant Type - Thrust, Propulsive Efficiency - Specific Impulse - Solid and Liquid propellant Rocket Engines TEXT BOOKS: 1. Thermal Engineering / Rajput / Lakshmi Publications. 2. Gas Turbines / V. Ganesan / TMH. 3. Thermal Engineering /P.L. Ballaney / Khanna Publishers, NewDelhi. REFERENCE BOOKS: 1. Gas Turbines and Propulsive Systems / P. Khajuria & S.P. Dubey / Dhanapatrai Pub. 2. Thermal Engineering / R.S. Khurmi & J.K. Gupta / S. Chand Pub. 3. Thermodynamics and Heat Engines / R. Yadav / Central Book Depot. COURSE OUTCOMES:  Recognize and recall the importance of thermal power plant and its thermodynamic analysis for improvement of efficiency.  Understand the operation of steam boiler, steam nozzle, condenser and steam turbine.  Able to do thermodynamic analysis for steam nozzles, condensers and steam turbines.  Evaluate the thermodynamic efficiency of gas turbine and jet propulsion systems.  Create the jet propulsion system and do the thermodynamic analysis for better efficiency. MRCET CAMPUS MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) DEPARTMENT OF MECHANICAL ENGINEERING APPLIED THERMODYNAMICS (R18A0308) COURSE OBJECTIVES UNIT - 1 UNIT - 2 UNIT - 3 CO1: To Explain in detail Basic Components of Rankine cycle. Methods to improve cycle performance. Types of Boilers with their working principles and applications. CO2: To Know the function of nozzles. Thermodynamic analysis of nozzles. Steam condensers and their requirement. CO3: To Study the different types of Turbines. Conditions for maximum efficiency. Parsons reaction turbine. UNIT - 4 CO4: To study the different types gas turbines. Applications of gas turbines. Efficiency improvement methods. UNIT - 5 CO5: To know the working principles of different Jet engines, thermodynamic cycles. Rocket engines and their working principles. s COURSE OUTLINE UNIT – 1 NO OF LECTURE HOURS: 15 LECTURE LECTURE TOPIC KEY ELEMENTS LEARNING OBJECTIVES (2 to 3 objectives) 1. Introduction to Rankine cycle: Schematic lay out p-V and T-s diagrams 2. Basic Components of Rankine Cycle and thermal power plant. Boiler, Turbine, Condenser, Pump. Understand the different components of the thermal power plant (B2) 3. Methods to improve the Rankine cycle efficiency Cycle efficiency Understand the working of Regenerative and reheat cycles (B2) 4. Types of Boilers and their Function Bob-cock Wilcox, La-mont, Loeffler boilers etc. To understand Function of boilers (B3) 5. High Pressure Boilers and Low pressure boilers Yarrow Boiler, Benson Boiler To understand the working principles of High pressure and Low pressure Boilers (B2) 6. Boiler mountings and accessories. Pressure Gauge, Fusible plug, water level indicator etc. To understand Function of mountings and accessories (B3) Understand the basics of Rankine Cycle. (B1) UNIT – 2 NO OF LECTURE HOURS: 10 LECTURE LECTURE TOPIC KEY ELEMENTS LEARNING OBJECTIVES (2 to 3 objectives) 1. Functions of Nozzles nozzles To understand the function of Nozzles.(B2) 2. Types of nozzles Convergent, divergent, Convergent-divergent nozzles Classification of nozzles (B4) 3. Thermodynamic analysis Expansion of steam To understand change in enthalpy (B2) 4. Steam condensers requirement Condensers To understand the requirement of condensers (B2) 5. Working principle of different types of condensers Working principles To understand the working of condensers (B2) To analyze the Each Component (B4) MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) DEPARTMENT OF MECHANICAL ENGINEERING UNIT – 3 NO OF LECTURE HOURS: 12 LECTURE LECTURE TOPIC KEY ELEMENTS LEARNING OBJECTIVES (2 to 3 objectives) 1. Classification of steam turbines Steam Turbines 2. Principle of operation of turbines Working Working principles of turbines.(B4) 3. To draw velocity diagrams Velocity, diagram To understand velocity diagrams(B2) 4. Maximum efficiency calculations Maximum efficiency To analyse maximum efficiency (B4) 5. Working of reaction turbine Reaction turbine, Parsons turbine. To be familiar with reaction turbines(B2) Types of condensers (B2) MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) DEPARTMENT OF MECHANICAL ENGINEERING UNIT – 4 NO OF LECTURE HOURS:10 LECTURE LECTURE TOPIC KEY ELEMENTS LEARNING OBJECTIVES (2 to 3 objectives) 1. Simple gas turbine plant Gas turbine To Understand the working of Gas turbines (B2). 2. Ideal cycle, essential components Components, cycle To understand the Ideal cycle and its components (B4) 3. Regeneration cycle Regeneration To Analyze the Regeneration cycle (B4). 4. Inter cooling and Reheating Inter cooling, Reheating To understand the Inter cooling and reheat cycles (B4) 5. Closed and Semi - closed cycle gas turbines Closed cycle, semi closed cycle To analyse the semi closed and semi closed gas turbines UNIT – 5 NO OF LECTURE HOURS: 10 LECTUR E LECTURE TOPIC KEY ELEMENTS LEARNING OBJECTIVES (2 to 3 objectives) 1. Introduction to Jet propulsion. Classification of Jet engines. Jet engine, Jet propulsion To understand jet engine and Jet propulsion. (B2) 2. Working Principles with schematic diagrams and representation on T-S diagram T-S diagram To analyse the T-S diagram (B2). 3. Thrust, Thrust Power and Propulsion Efficiency Thrust, Propulsion efficiency To Understand the thrust power and propulsion (B2). 4. Needs and Demands met by Turbo jet Turbo Jet To Understand the needs of turbo jet (B3) 5. Thermodynamic Cycle, Performance Evaluation Performance To analyse thermodynamic analysis (B4) 6. Rockets and their working principles Rockets To Understand the working of Rocket engines (B2) B. Tech (MECH) R-18 Mapping of COs and POs: Course Outcomes PO1 PO2 PO3 PO4 PO5 PO6 PO7 PO8 PO9 PO10 PO11 PO12 PSO1 PSO2 PSO3 C308.1 X X X X X X X X X - - X X X X C308.2 X X X X - X X X - - - X X X X C308.3 X X X X - X X X - - - X X X X C308.4 X X X - - X X X - - - X X X X C308.5 X X X - - X X X X - - X X X X Course Outcomes PO1 PO2 PO3 PO4 PO5 PO6 PO7 PO8 PO9 PO10 PO11 PO12 PSO1 PSO2 PSO3 C308.1 3 3 2 1 1 3 3 3 1 - - 3 3 3 2 C308.2 2 3 2 1 - 2 2 2 - - - 2 3 2 3 C308.3 2 3 2 1 - 2 2 2 - - - 2 3 2 3 C308.4 2 2 3 - - 2 2 3 - - - 3 2 2 2 C308.5 3 2 3 - - 2 2 3 2 - - 3 2 2 2 Mode of Evaluation: X    MRCET CAMPUS 70% of marks for External Evaluation. 24% of marks for Internal Evaluation. 6% of marks for Continuous Evaluation assignments. UNIT 1 BASIC CONCEPTS & BOILERS Course Objective: The purpose of this course is to enable the student to gain an understanding of how thermodynamic principles govern the behavior of various systems Course Outcome: To be able to describe the most important combustion concepts and problems in concern to power plants. DEPARTMENT OF MECHANICAL ENGINEERING Rankine Cycle: Rankine cycle is the theoretical cycle on which steam turbine works. In an ideal Rankine cycle, the system executing the cycle undergoes a series of four processes: two isentropic (reversible adiabatic) processes alternated with two isobaric processes: DEPARTMENT OF MECHANICAL ENGINEERING    Isentropic expansion (expansion in a steam turbine) – Steam from the boiler expands adiabatically from state 1 to state 2 in a steam turbine to produce work and then is discharged to the condenser (partially condensed). The steam does work on the surroundings (blades of the turbine) and loses an amount of enthalpy equal to the work that leaves the system. The work done by turbine is given by WT = H1 – H2. Again the entropy remains unchanged. Isobaric heat rejection (in a heat exchanger) – In this phase the cycle completes by a constant-pressure process in which heat is rejected from the partially condensed steam. There is heat transfer from the vapor to cooling water flowing in a cooling circuit. The vapor condenses and the temperature of the cooling water increases. The net heat rejected is given by Qre = H2– H3 Isentropic compression (compression in centrifugal pumps) – The liquid condensate is compressed adiabatically from state 3 to state 4 by centrifugal pumps (usually by condensate pumps and then by feed water pumps). The liquid condensate is pumped from the condenser into the higher pressure boiler. In this process, the surroundings do work on the fluid, increasing its enthalpy (h = u+pv) and compressing it (increasing its pressure). On the other hand the entropy remains unchanged. The work required for the compressor is given by WPumps = H4 – H3. DEPARTMENT OF MECHANICAL ENGINEERING  Isobaric heat addition (in a heat exchanger – boiler) – In this phase (between state 2 and state 3) there is a constant-pressure heat transfer to the liquid condensate from an external source, since the chamber is open to flow in and out. The feed water (secondary circuit) is heated from to the boiling point (2 → 3a) of that fluid and then evaporated in the boiler (3a → 3). The net heat added is given by Qadd = H1 – H4 Thermal Efficiency of Rankine Cycle DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING Boilers Steam is extensively used for various applications such as power production, industrial processes, work interaction, heating etc. With the increasing use of steam in different engineering systems the steam generation technology has also undergone various developments starting from 100 B.C. when Hero of Alexandria invented a combined reaction turbine and boiler. Boiler, also called steam generator is the engineering device which generates steam at constant pressure. It is a closed vessel, generally made of steel in which vaporization of water takes place. Heat required for vaporization may be provided by the combustion of fuel in furnace, electricity, nuclear reactor, hot exhaust gases, solar radiations etc. Earlier boilers were closed vessels made from sheets of wrought iron which were lapped, riveted and formed into shapes of simple sphere type or complex sections such as the one shown in Fig. 1.1. It is the ‘Wagon boiler’ of Watt developed in 1788. According to A.S.M.E. (American Society of Mechanical Engineers, U.S.A.) code a boiler is defined as a combination of apparatus for producing, furnishing or recovering heat together with the apparatus for transferring the heat so made available to water which could be heated and vaporized to steam form. Types of Boilers Boilers are of many types. Depending upon their features they can be classified as given under: (a) Based upon the orientation/axis of the shell: According to the axis of shell boiler can be classified as vertical boiler and horizontal boiler. (i) Vertical boiler has its shell vertical. (ii) Horizontal boiler has its shell horizontal. DEPARTMENT OF MECHANICAL ENGINEERING (iii) Inclined boiler has its shell inclined. (b) Based upon utility of boiler: Boilers can be classified as (i) Stationery boiler, such boilers are stationery and are extensively used in power plants, industrial processes, heating etc. (ii) Portable boiler, such boilers are portable and are of small size. These can be of the following types, Locomotive boilers, which are exclusively used in locomotives. Marine boiler, which are used for marine applications. (c) Based on type of firing employed: According to the nature of heat addition process boilers can be classified as, (i) Externally fired boilers, in which heat addition is done externally i.e. furnace is outside the boiler unit. Such as Lancashire boiler, Locomotive boiler etc. (ii) Internally fired boilers, in which heat addition is done internally i.e. furnace is within the boiler unit. Such as Cochran boiler, Bobcock Wilcox boiler etc. (d) Based upon the tube content: Based on the fluid inside the tubes, boilers can be, (i) Fire tube boilers, such boilers have the hot gases inside the tube and water is outside surrounding them. Examples for these boilers are, Cornish boiler, Cochran boiler, Lancashire boiler, Locomotive boiler etc. (ii) Water tube boilers, such boilers have water flowing inside the tubes and hot gases surround them. Examples for such boilers are Babcock-Wilcox boiler, Stirling boiler, La-Mont boiler, Benson boiler etc. (e) Based on type of fuel used: According to the type of fuel used the boilers can be, (i) Solid fuel fired boilers, such as coal fired boilers etc. (ii) Liquid fuel fired boilers, such as oil fired boilers etc. (iii) Gas fired boilers, such as natural gas fired boilers etc. (f) Based on circulation: According to the flow of water and steam within the boiler circuit the boilers may be of following types, (i) Natural circulation boilers, in which the circulation of water/steam is caused by the density difference which is due to the temperature variation. (ii) Forced circulation boilers, in which the circulation of water/steam is caused by a pump i.e. externally, assisted circulation. (g) Based on extent of firing: According to the extent of firing the boilers may be, (i) Fired boilers, in which heat is provided by fuel firing. (iii) Unfired boilers, in which heat is provided by some other source except fuel firing such as hot flue gases etc. (iv) Supplementary fired boilers, in which a portion of heat is provided by fuel firing and remaining by some other source. 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Boiler Accessories: These are the devices which are used as integral parts of a boiler and help in running efficiently. Various boiler accessories are: 1. Feed pump 2. Super heater 3. Economiser 4. Air Preheater 5. Injector 1. Feed pump It is used to deliver water to the boiler. A feed pump may be of centrifugal type or reciprocating type. But a double acting reciprocating pump is commonly used as a feed pump. 2. Super Heater Function It superheats the steam generated by the boiler and increases the temperature steam above saturation temperature at constant pressure. Location Superheaters are placed in the path of flue gases to recover some of their heat. In bigger installations, the superheaters are placed in an independently fired furnace. Such superheaters are called separately fired or portable superheaters. DEPARTMENT OF MECHANICAL ENGINEERING Construction There are many types of super heaters. A combination type of radiant and convective super heater is shown in figure. Both these super heaters are arranged in series in the path of flue gases. Radiant super heater receives heat from the burning fuel by radiation process. Convective super heater is placed adjacent to the furnace wall in the path of flue gases. It receives heat by convection. Working Steam stop valve is opened. The steam (wet or dry) from the evaporator drum is passed through the superheated tubes. First the steam is passed through the radiant superheater and then to the convective super heater. The steam is heated when it passes through these super heaters and converted into superheated steam. This superheated steam is supplied to the turbine through a valve. Applications This type of super heaters is used in modern high pressure boilers. Advantages of superheated steam (super heaters) 1. Work output is increased for the same quantity of steam. 2. Loss due to condensation of steam in the steam engine and is the steam mains is minimized. 3. Capacity of the plant is increased. 4. Thermal efficiency is increased since the temperature of superheated steam is high. DEPARTMENT OF MECHANICAL ENGINEERING 3. Economiser Function: An economizer pre –heats (raise the temperature) the feed water by the exhaust flue gases. This pre –heated water is supplied to the boiler from the economizer. Location: An economizer is placed in the path of the flue gases in between the boiler and the air pre – heater or chimney. Construction: An economizer used in modern high pressure boilers is shown by a line sketch. It consists of a series of vertical tubes. These tubes are hydraulically pressed into the top and bottom headers. The bottom header is connected to feed pump. Top header is connected to the water space of the boiler. It is provided with a safety valve which opens when water pressure exceeds a certain limit. To keep the surface of the tubes clean from soot and ash deposits, scrapers are provided in the tubes. These scrapers are slowly moved up and down to clean the surfaces of the tubes. The action of adjacent pairs of scraper is in opposite direction. i.e., when one scraper moves up, the other moves down. Economizers may be parallel or counter-flow types. When the gas flow and water flow are in the same direction, it is called parallel flow economizer. In counter-flow, the gas flow and water flow are in opposite direction. Working DEPARTMENT OF MECHANICAL ENGINEERING The feed water is pumped to the bottom header and this water is carried to the top header through a number of vertical tubes. Hot flue gases are allowed to pass over the external surface of the tubes. The feed water which flows upward in the tubes is thus heated by the flue gases. This pre-heated water is supplied to the boiler. Advantages 1. Feed water to the boiler is supplied at high temperature. Hence heat required in the boiler is less. Thus fuel consumption is less. 2. Thermal efficiency of the plant is increased. 3. Life of boiler is increased. 4. Loss of heat in flue gases is reduced. 5. Steaming capacity is increased. 4. Air pre-heater Function Air pre-heater pre-heats (increases the temperature) the air supply to the furnace with the help of hot the gases. Location It is installed between the economizer and the chimney. Construction A tubular type air pre-heater is shown in figure. It consists of a large number of tubes. Flue gases pass through the tube. Air flows over the tubes. Baffles are provided to pass the air number of times over the tubes. A soot hopper is provided at the bottom to collect the soot. Working DEPARTMENT OF MECHANICAL ENGINEERING Hot flue gases pass through the tubes of air pre-heater after leaving the boiler or economizer. Atmospheric air is allowed to pass over these tubes. Air and flue gases flow in opposite directions. Baffles are provided in the air pre-heater and the air passes number of times over the tubes. Heat is absorbed by the air from the flue gases. This pre-heater air is supplied to the furnace to air combustion. Advantages 1. 2. 3. 4. Boiler efficiency is increased. Evaporative rate is increased. Combustion is accelerated with less soot, smoke and ash. Low grade and inferior quality fuels can be used. DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING INDUSTRIAL APPLICATIONS Industrial Applications of Rankine Cycle DEPARTMENT OF MECHANICAL ENGINEERING Mostly Industrial Boilers Used in 1. Food Processing Industry 2. Milk & Dairies Industry 3. Rice Mills Industry 4. Textile Industry 5. Pharmaceuticals Industry 6. Rubber Industry 7. Thermocol Industry 8. Plywood Industry 9. Metal Forging Industry 10. Health Care Industry 11. Chemical Industry 12. Automobiles Industry 13. Construction Industry 14. Paper Industry 15. Refineries & Distilleries 16. Sugar Industry High pressure boilers are used in industrial, commercial, or manufacturing applications for central heating systems,autoclaves, hot water supply and other important factory or plant processes. DEPARTMENT OF MECHANICAL ENGINEERING TUTORIAL QUESTIONS Theory Questions: 1. Mention the different operations of Rankine cycle. Draw the schematic for an ideal Rankine cycle. Draw p-v, T-s and h-s diagrams for this cycle. 2. Explain regeneration cycle with the help of neat sketches of layout, p-v and T-s plots. 3. What are the different thermodynamic variables affecting efficiency and output of Rankine cycle. Explain their influence on Rankine cycle. 4. Draw diagram of ‘reheat cycle’ and state the advantages and disadvantages of reheating 5. Sketch the process diagram of a ‘regenerative cycle’. State the advantages of regenerative cycle over simple Rankine cycle. 6. How boilers are classified on different accounts with examples for each category. 7. Write any six comparisons between fire tube and water tube boilers. 8. Explain the working of Babcock and Wilcox boiler with the help of a neat sketch. 9. Sketch and describe a Cochran boiler. What are its special features? 10. Explain Lancashire boiler with neat sketch. 11. What are the functions of boiler mountings and accessories? Explain any one accessory 12. Explain vilox Boiler with Neat Sketch? 13. Explain Lamont Boiler with Neat sketch NUMERICAL PROBLEMS 1. Consider a regenerative vapour power cycle with a feed water heater. The steam enters the first stage turbine at 8 MPa, 500oC and expands to 0.7 MPa, where some of the steam is extracted and diverted to feed water heater operating at 0.7 MPa. The remaining steam expands through the second stage turbine to a condenser pressure of 0.008 MPa. The saturated liquid exits the feed water heater at 0.7 MPa. The isentropic efficiency of each turbine is 85%, while each pump operates isentropically. If the net power output of the cycle is 105 MW, determine 1. Thermal efficiency of the cycle 2. The mass flow rate of steam entering the first turbine stage. 2. In a Rankine cycle, the steam at inlet to turbine is saturated at pressure of 30 bar and exhaust pressure is 0.25 bar. Determine (i) The pump work (ii) Turbine work (iii) DEPARTMENT OF MECHANICAL ENGINEERING ASSIGNMENT QUESTIONS Rankine efficiency (iv) Condenser heat flow (v) dryness at the end of expansion. Assume flow rate of 10 kg/s. 3. A steam power plant equipped with combined reheat and regenerative arrangements is supplied with steam to H.P turbine at 80 bar and 470ºC. For feed heating a part of steam is extracted at 7 bar and the remainder of steam is reheated to 350ºC in a reheater and then expanded in L.P turbine down to 0.035 bar. Determine (i) amount of steam bled off for feed heating (ii) amount of steam in L.P turbine (iii) heat supplied in boiler and reheater (iv) Output of turbine (v) cycle efficiency. ASSIGNMENT QUESTIONS 1. A power generating plant uses steam as working fluid and operates at boiler pressure of 50 bar, dry saturated and a condenser pressure of 0.1bar. Calculate for these limits:The cycle efficiency; ii) the work ratio and specific steam consumption for Rankine cycle. Take pumping work also into account 2. a) Explain a regenerative cycle with a diagram b) Draw diagram of ‘reheat cycle’ and state the advantages and disadvantages of reheating 3. a) Explain any two of the following with neat sketches i) Super heater ii) Air Preheater iii) Economizer b) List the advantages of high pressure boilers. 4. Explain the working of Babcock and Wilcox boiler with the help of a neat sketch. 5. In a reheat cycle steam enters the H.P turbine at 100 bar and 500ºC. The expansion is continued to a pressure of 8.5 bar with isentropic efficiency of 80%. There is a pressure drop of 1.5 bar in the reheater and then steam enters the L.P turbine at 7 bar and 500ºC in which expansion is continued to a back pressure of 0.04 bar with isentropic efficiency of 85%.Determine i) thermal efficiency ii) specific steam consumption. DEPARTMENT OF MECHANICAL ENGINEERING UNIT 2 STEAM NOZZLES & STEAM CONDENSERS Course Objective: Applications and the principles of thermodynamics to components and systems. Course Outcome: To be able to analyze energy distribution in turbines ,nozzles and condensers DEPARTMENT OF MECHANICAL ENGINEERING Steam Nozzles and Types Nozzle is a duct by flowing through which the velocity of a fluid increases at the expense of pressure drop. if the fluid is steam, then the nozzle is called as Steam nozzle. The flow of steam through nozzles may be taken as adiabatic expansion. The steam possesses very high velocity at the end of the expansion, and the enthalpy decreases as expansion occurs. Friction exists between the steam and the sides of the nozzle; heat is produced as the result of the resistance to the flow. The phenomenon of super saturation occurs in the steam flow through nozzles. This is because of the time lag in the condensation of the steam during the expansion. The area of such duct having minimum cross-section is known as throat. A fluid is called compressible if its density changes with the change in pressure brought about by the flow. If the density changes very little or does not changes, the fluid is said to be incompressible. Generallythe gases and vapors are compressible, whereas liquids are incompressible. Types of Nozzles: There are three types of nozzles 1. Convergent nozzle 2. Divergent nozzle 3. Convergent-divergent nozzle. Convergent Nozzle: A typical convergent nozzle is shown in the Fig.1. In a convergent nozzle, the cross sectional area decreases continuously from its entrance to exit. It is used in a case where the back pressure is equal to or greater than the critical pressure ratio. Fig 1. Convergent nozzle Divergent nozzle: The cross sectional area of divergent nozzle increases continuously from its entrance to exit. It is used in a case where the back pressure is less than the critical pressure ratio. DEPARTMENT OF MECHANICAL ENGINEERING Fig 2. Divergent nozzle Convergent – Divergent nozzle: In this condition, the cross sectional area first decreases from its entrance to the throat and then again increases from throat to the exit. This case is used in the case where the back pressure is less than the critical pressure. Also, in present day application, it is widely used in many types of steam turbines. Fig 3. Convergent-Divergent nozzle Flow of steam Through Nozzle Supersaturated flow or metastable flow of in Nozzles: As steam expands in the nozzle, the pressure and temperature in it drop, and it is likely that the steam start condensing when it strikes the saturation line. But this is not always the situation. Due to the high velocities, the time up to which the steam resides in the nozzle is small, and there may not be sufficient time for the needed heat transfer and the formation of liquid droplets due to condensation. As a result, the condensation of steam is delayed for a while. This phenomenon is known as super saturation, and the steam that remains in the wet region without holding any liquid is known as supersaturated steam. The locus of points where condensation occurs regardless of the initial temperature and pressure at the entrance of the nozzle is called the Wilson line. The Wilson line generally lies between 4 and 5 percent moisture curves in the saturation region on the h-s diagram in case of steam, and is often taken as 4 percent moisture line. The phenomenon of super saturation is shown on the h-s chart below: DEPARTMENT OF MECHANICAL ENGINEERING Fig 4. The h-s diagram for the expansion of steam in the nozzle Effects of Supersaturation: The following are the effects of supersaturation in a nozzle. 1. The temperature at which the steam becomes supersaturated will be less than the saturation temperature corresponding to that pressure. Therefore, supersaturated steam will have the density more than that of equilibrium condition which results in the increase in the mass of steam discharged. 2. Supersaturation causes the specific volume and entropy of the steam to increase. 3. Supersaturation reduces the heat drop. Thus the exit velocity of the steam is reduced. 4. Supersaturation increases the dryness fraction of the steam. Effect of Friction on Nozzles: 1. Entropy is increased. 2. The energy available decreases. 3. Velocity of flow at the throat get decreased. 4. Volume of flowing steam is decreased. 5. Throat area required to discharge a given mass of steam is increased. Continuity and steady flow energy equations through a certain section of the nozzle: Where m denotes the mass flow rate, v is the specific volume of the steam, A is the area of cross-section and C is the velocity of the steam. For steady flow of the steam through a certain apparatus, principle of conservation of energy states: h1 + C12/2 + gz1 + q = h2 + C22/2 + gz2 + w For nozzles, changes in potential energies are negligible, w = 0 and q = 0. DEPARTMENT OF MECHANICAL ENGINEERING h1 + C12 /2 = h2 + C22 /2 which is the expression for the steady state flow energy equation. DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING Requirements of Steam Condensing Plant 1. Condenser: It is a closed vessel used to condense the steam. The low pressure steam gives off its heat to the coolant (here water from cooling tower) and gets converted into water during the process of condensation. 2. Condensate Extraction Pump: It is a pump which is installed in between the condenser and hot well. It transfers the condensate from the condenser to the hot well. 3. Hot Well: It is a sump that lies in between the condenser and boiler. It receives the condensate from the condenser by condensate pump. The feed water is transferred from the hot well to the boiler. 4. Boiler Feed Pump: It is a pump installed in between the hot well and boiler. It pumps the feed water from the hot well to the boiler. And this is done by increasing the pressure of condensate above boiler pressure. 5. Air Extraction Pump: It is a pump used to extracts or removes the air from the steam condenser. 6. Cooling Tower: It is a tower which contains the cold water and this water is made to circulate within the condenser for cooling of steam. DEPARTMENT OF MECHANICAL ENGINEERING 7. Cooling Water Pump: It is a pump lies in between the cooling tower and condenser. It circulates the cooling water through the condenser. Working The steam condenser receives the exhaust steam from one end and comes in contact with the cooling water circulated within it form the cooling tower. As the low pressure steam comes in contact with the cooling water, it condenses and converts into water. It is connected to the air extraction pump and condensate extraction pump. After the condensation of steam, the condensate is pumped to the hot well with the help of condensate extraction pump. The air extraction pump extracts the air from the condenser and creates the vacuum inside it. The vacuum created helps in the circulation of cooling water and flow of condensate downward. Surface Condensers Surface condenser is a type of steam condenser in which the steam and cooling water do not mix with each other. And because of this, the whole condensate can be used as boiler feed water. It is also called as non-mixing types condenser. DEPARTMENT OF MECHANICAL ENGINEERING The figure above shows the longitudinal section of a two pass surface condenser. It consists of a horizontal cylindrical vessel made of cast iron and packed with tubes. The cooling water flows through these tubes. The ends of the condensers are cut off by the perforated type plates. The tubes are fixed into these perforated type plates. It is fixed in such a manner that any leakage of water into the center of condensing space is prevented. The water tubes are passed horizontally through the main condensing space. The exhaust steam from the turbine or engine enters at the top and forced to move downward due to the suction of the air extraction pump. In this steam condenser, the cooling water enters into boiler through lower half of the tubes in one direction and returns in opposite direction through the upper half as shown in the figure above. This type of condenser is used in ships as it can carry only a limited quantity of water for the boiler. It is also widely used for the land installation where there is a scarcity of good quality of water. Types of Surface Condensers The surface condenser on the basis of direction of flow of condensate, the arrangement of the tubing system and the position of the extraction pump are classified as (i) Down Flow In Down flow surface condenser, the steam enters at the top of the condenser and flows downwards over the tubes due to the gravity and air extraction pumps. The condensate gets collected at the bottom and then pumped with the help of condensate extraction pump. The pipe of dry air extraction pump is provided near the bottom and it is covered by baffle plates so as to prevent the entry of the condensate into it. The steam in down flow condenser flows perpendicular to the direction of flow of cooling water, so it is also called as cross-surface condenser. (ii) Central Flow In central flow condenser, the steam enters at the top of the condenser and flows in downward direction. In this the suction pipe of the air extraction pump is provided in the center of the tube nest as shown in the figure. Due to this placement of the suction pipe in the center of the tube nest, the exhaust DEPARTMENT OF MECHANICAL ENGINEERING steam flows radially inward over the tubes towards the suction pipe. The condensate is collected at the bottom of the condenser and pumped to the hot well. We can say that it is the improved form of the down flow surface condenser. (iii) Regenerative In regenerative surface condensers, the condensate is heated by the use of regenerative method. In that the condensate is passed through the exhaust steam coming out from the turbine or engine. This raises its temperature and it is used as the feed water for the boiler. (iv) Evaporative In evaporative surface condensers, the steam enters at the top of the condenser in a series of pipes over which a film of cold water is falling. At the same time, current of air is made to circulate over the film of water. As the air circulates over the water film, it evaporates some of the cooling water. As a result of this rapid evaporation, the steam circulating inside the series of pipes gets condensed. Remaining cooling water that left is collected at an increased temperature and reused. It is brought to the original temperature by adding required quantity of cold water.     Advantages of Steam Condenser It increases the efficiency of the plant. It reduces the back pressure of the steam and as a result of this, more work can be done. It reduces the temperature of the exhaust steam and this allows to obtain more work. It allows the reuse of condensate for the feed water and hence reduces the cost of power generation. DEPARTMENT OF MECHANICAL ENGINEERING  The temperature of the condensate is more than the feed water. This reduces the supply of heat per kg of steam. Comparison of Jet and Surface Condenser in Tabular Form S.no Jet Condenser Surface Condenser 1. Exhaust steam and cooling water mixed with Exhaust steam and cooling water are not mixed each other. with each other. 2. It is less suitable for high capacity plants. 3. The condensing plant using this type of steam The condensing plant using surface condenser is condenser is simple and costly and economical. complicated. 4. Condensate is wasted and cannot be reused. The condensate is reused. 5. Less quantity of circulating water is required. Large quantity of circulating water is required. 6. It has low maintenance cost. It has high maintenance cost. 7. In jet condenser, more power is required for In surface condenser, less power is required for the air pump. the air pump. 8. High power is required for water pumping. DEPARTMENT OF MECHANICAL ENGINEERING It is more suitable for high capacity plants. Less power is required for water pumping. DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING INDUSTRIAL APPLICATIONS Industrial Applications. Nozzles are used in 1. Steam turbines, gas turbines, water turbines and in jet engines, Jet propulsion. 2. Nozzles are used for flow measurement e.g. in venturimeter. 3. Nozzles are used to remove air from a condenser. 4. Injectors for pumping feed water to boilers. Condensers have proven to be reliable and are chosen for applications throughout the world, a few of which are below: 1. Power 2. Chemical processing 3. Refinery 4. HVAC 5. Low oxygen condensate 6. Marine DEPARTMENT OF MECHANICAL ENGINEERING TUTORIAL QUESTIONS Theory Questions: 1. Mention various types of nozzles and distinguish their features. 2. Define nozzle velocity coefficient and how it is related to nozzle efficiency and discharge coefficient as applied to nozzles. 3. Derive an expression for maximum mass flow per unit area of flow through a convergent- divergent nozzle when steam expands isentropic ally from rest. 4. Discuss the process of super-saturation in steam nozzles with the help of enthalpy entropy diagram. 5. Define degree of super-saturation and degree of under-cooling. Explain in detail the physical significance of abrupt change at Wilson`s line. 6. Differentiate the terms “over expanding” and “under expanding” as applied to a fluid flow through a nozzle. 7. What are the components of a steam condensing plant? What are the functions of each component working in steam condensing plant? 8. Classify steam condensers. What are the differences between the jet Condensers and surface condensers? List out the advantages of condenser in a steam power plant. 9. Draw the schematic diagram of parallel flow jet condenser. 10. Draw the schematic diagram of Evaporative condenser and Explain Briefly? Numerical Problems: 1. In a convergent-divergent nozzle, the steam enters at 15 bar and 3000C and leaves at a pressure of 2 bar. The inlet velocity to the nozzle is 150 m/s. Find the required throat and exit areas for a mass flow rate of 1 kg/s. Assume nozzle efficiency to be 90 percent and Cps = 2.4 kJ/kg.K 2. A convergent nozzle is used to expand ethane gas at 780 kPa and 3500K isentropically into a chamber at 370 kPa. Find the nozzle exit area for a mass flow rate of 1400 kg/s. Assume the initial velocity is zero, C p=1.9 kJ/kgK, R=277 J/kg K and A. INDEX =1.17 3. Dry saturated steam expands through a nozzle from a pressure of 13.7 bar down to 9.6 bar. Assuming the flow to be frictionless and adiabatic, estimate velocity of steam jet. DEPARTMENT OF MECHANICAL ENGINEERING ASSIGNMENT QUESTIONS 4. For a nozzle, show the area on p-v diagram which represents the conversion of heat energy to kinetic energy. Prove that this area equals the heat drop during expansion. Assume isentropic flow in a nozzle. Further show the expansion for steam on T-s and h-s charts and for air on T-s chart. ASSIGNMENT QUESTIONS 1. What are the differences between the jet Condensers and surface condensers? Draw the schematic diagram of Evaporative condenser and Explain Briefly? 2. Starting from the fundamentals, show that the maximum discharge through the nozzle,the ratio of throat pressure to inlet pressure is given by (2/n+1) n/n-1, where n is the index for isentropic expansion through the nozzle 3. In a convergent-divergent nozzle, the steam enters at 15 bar and 300oC and leaves at a pressure of 2 bar. The inlet velocity to the nozzle is 150 m/s. Find the required throat and exit areas for a mass flow rate of 1 kg/s. Assume nozzle efficiency to be 90 percent and Cps = 2.4 kJ/kg.K DEPARTMENT OF MECHANICAL ENGINEERING UNIT 3 STEAM TURBINES & REACTION TURBINE Course Objective: Student have knowledge of methods of analysis and design of complicated thermodynamic systems Course Outcome: To understand the velocity triangles and boilers concepts in a lucid manner. 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Waste Plants: Steam turbines help generate the power needed to harness energy from wastes. Oil & Gas: Used as a pump drive or a compressor, steam turbines support dozens of operations in the oiland gas industry. Sugar Mills: Offering high levels of efficiency and sustainable operations, steam turbines are used to produce green carbon-dioxide energy from bagasse. Some of the most popular applications of a steam turbine in different industries include the following: 1. Combined Heat and Power Steam turbines are an essential component of most CHP systems. They support combined heat and power systems that are used to power industrial processes, under conditions where waste fuels are available for the boiler to safely utilize. When used for CHPs, the steam emitted by the steam turbine can be used directly. Steam turbine powered CHPs are typically found in paper mills, where there is an abundance of waste fuels ranging from black liquor to hog fuel, each equally successfully in powering the boiler. They can also be found in chemical plants that make excessive use of steam turbines; followed by their use of metals. 2. Driving Mechanical Equipment Steam turbines are a far more efficient alternative to electrical power. Especially when it comes to driving different equipment like air compressors, boiler feed water pumps, refrigerator chillers, etc. 3. District Heating & Cooling Systems Different institutions throughout different cities rely on district cooling and heating systems. These systems usually have a steam turbine placed between the boiler and the distribution system or placed as a replacement for a pressure reduction station.It is to be noted that, more often, boilers are capable of producing moderate-pressure steam while the distribution requires low pressure steam. Bridging this gap between the two, a steam turbine generates energy using the high pressure steam and emits low pressure steam into the distribution system. DEPARTMENT OF MECHANICAL ENGINEERING 4. Combined Cycle Power Plants Steam turbines allow power plants to generate power using a gas turbine and utilize gas and heat produced in the process to generate steam that, in turn, produces additional power. Combined cycle power plants supported by steam turbines are capable of producing or accomplishing electric generation efficiencies extending beyond the 50-percent mark and are used in large industrial applications. Reaction Turbine    Reaction turbine is used in wind power mills to generate electricity It is most widely used turbine in hydro-power plants, to generate electricity. It is the only turbine to get maximum power output from a low available water head and high velocity other than cross-flow turbine which not that efficient. DEPARTMENT OF MECHANICAL ENGINEERING TUTORIAL QUESTIONS Theory Questions: 1. What is turbine and classify them. 2. Derive the expression for maximum efficiency of reaction turbine. What is the condition for maximum blade efficiency of a 50% reaction turbine and its value? 3. Derive an expression for optimum stage efficiency of a reaction turbine. 4. Write a note on degree of reaction. Derive an expression for degree of reaction and show that inlet and outlet velocity triangles are symmetrical for a 50% degree of reaction turbine. 5. Sketch how efficiency varies with blade-steam velocity ratio. 6. Deduce an expression for work done per stage of a reaction blading? 7. Explain with neat sketch of impulse turbine with Pressure and velocity curves Numerical Problems: 1. In a single-stage impulse turbine, the steam jet leaves the nozzles at 20º to the plane of the wheel at a speed of 670 m/s and it enters the moving blades at an angle of 35º to the drum axis. The moving blades are symmetrical in shape. Determine the blade velocity and diagram efficiency. 2. Write short notes on De-Laval Turbine and about its features. Steam leaves the nozzle of a single-stage impulse turbine at 840 m/s. The nozzle angle is 18º and the blade angles are 29º at the inlet and outlet. The friction coefficient is 0.9. Calculate (i) blade velocity (ii) steam mass flow rate in kg/h to develop 300 kW power. ASSIGNMENT QUESTION 1. Discuss the relative advantages and disadvantages of gas turbines and steam turbines. 2. Define the following as related to steam turbines. i) Blade Speed ratio ii) blade velocity coefficient iii) diagram efficiency iv) stage efficiency 3. a) Prove that for a 50% reaction turbines α=φ and θ=β b) Explain the difference between an impulse turbine and a reaction turbine 4. Derive the expression for maximum blade efficiency of a single stage impulse turbine. 5. Write the expression for blade efficiency for a single stage reaction turbine for getting the maximum blade efficiency. DEPARTMENT OF MECHANICAL ENGINEERING UNIT 4 GAS TURBINES Course Objective: Student have knowledge of methods of analysis and design of complicated thermodynamic systems Course Outcome: To be able to recognize main and supplementary elements of turbines and define operational principles. DEPARTMENT OF MECHANICAL ENGINEERING Brayton Cycle Brayton cycle, popularly used for gas turbine power plants comprises of adiabatic compression process, constant pressure heat addition, adiabatic expansion process and constant pressure heat release process. A schematic diagram for air-standard Brayton cycle is shown in Fig. 4.1. Simple gas turbine power plant working on Brayton cycle is also shown here. Thermodynamic processes: cycle shows following 1-2: Adiabatic compression, involving (–ve) work, WC in compressor. 2-3 : Constant pressure heat addition, involving heat Qadd in combustion chamber or heat exchanger. 3-4: Adiabatic expansion, involving (+ve) work, WT in turbine. 4-1: Constant pressure heat rejection, involving heat, Qrejected in atmosphere or heat exchanger. In the gas turbine plant layout shown process 1–2 (adiabatic compression) is seen to occur DEPARTMENT OF MECHANICAL ENGINEERING in compressor, heat addition process 2–3 occurs in combustion chamber having open type arrangement and in heat exchanger in closed type arrangement. Process 3–4 of adiabatic expansion occurs in turbine. In open type arrangement exhaust from turbine is discharged to atmosphere while in closed type, heat rejection occurs in heat exchanger. In gas turbine plant of open type, air entering compressor gets compressed and subsequently brought up to elevated temperature in combustion chamber where fuel is added to high pressure air and combustion occurs. High pressure and high temperature combustion products are sent for expansion in turbine where its’ expansion yields positive work. Expanded combustion products are subsequently discharged to atmosphere. Negative work required for compression is drawn from the positive work available from turbine and residual positive work is available as shaft work for driving generator. In gas turbine plant of closed type the working fluid is recycled and performs different processes without getting contaminated. Working fluid is compressed in compressor and subsequently heated up in heat exchanger through indirect heating. High pressure and high temperature working fluid is sent for getting positive work from turbine and the expanded working fluid leaving turbine is passed through heat exchanger where heat is picked up from working fluid. Thus, the arrangement shows that even costly working fluids can also be used in closed type as it remains uncontaminated and is being recycled. Air standard analysis of Brayton cycle gives work for compression and expansion as; WC = m1 · (h2 – h1) WT = m3 · (h3 – h4) for air standard analysis, m1 = m3, where as in actual cycle m3 = m1 + mf , in open type gas turbine m3 = m1, in closed type gas turbine For the fuel having calorific value CV the heat added in air standard cycle; DEPARTMENT OF MECHANICAL ENGINEERING Qadd = m1(h3 – h2), whereas Qadd = mf × CV for actual cycle. Net work = WT – WC Wnet = {m3 (h3 – h4) – m1(h2 – h1)} Thus, it is obvious from the expression of efficiency that it depends only on pressure ratio (r) and nature of gas (γ). For pressure ratio of unity, efficiency shall be zero. For a particular gas the cycle efficiency increases with increasing pressure ratio. Here the variation of efficiency with pressure ratio is shown for air (γ= 1.4) and monatomic gas as DEPARTMENT OF MECHANICAL ENGINEERING Regenerative gas turbine cycle Regenerative air standard gas turbine cycle shown ahead in Fig. 4.3 has a regenerator (counter flow heat exchanger) through which the hot turbine exhaust gas and comparatively cooler air coming from compressor flow in opposite directions. Under ideal conditions, no frictional pressure drop occurs in either fluid stream while turbine exhaust gas gets cooled from 4 to 4' while compressed air is heated from 2 to 2'. Assuming regenerator effectiveness as 100% the temperature rise from 2–2' and drop from 4 to 4' is shown on T-S diagram. Thus, thermodynamically the amount of heat now added shall be Qadd, regen = m (h3 – h2 ') Where as without regenerator the heat added; Qadd = m (h3 – h2) Here it is obvious that, Qadd, regen < Qadd This shows an obvious improvement in cycle thermal efficiency as every thing else remains same. Net work produced per unit mass flow is not altered by the use of regenerator. DEPARTMENT OF MECHANICAL ENGINEERING eheat cycle gas turbine Reheat gas turbine cycle arrangement is shown in Fig. 4.4. In order to maximize the work available from the simple gas turbine cycle one of the option is to increase enthalpy of fluid entering gas turbine and extend its expansion upto the lowest possible enthalpy value. C: Compressor CC: Combustion chamber G: Generator chamber f: HPT: High pressure turbine LPT: Low pressure turbine RCC: Reheat combustion Fuel This can also be said in terms of pressure and temperature values i.e. inject fluid at high pressure and temperature into gas turbine and expand upto lowest possible pressure value. Upper limit at inlet to turbine is limited by metallurgical limits while lower pressure is limited to near atmospheric pressure in case of open cycle. Here in the arrangement shown ambient air enters compressor and compressed air at high pressure leaves at 2. Compressed air is injected into combustion chamber for increasing its temperature up to desired turbine inlet temperature at state 3. High pressure and high temperature fluid enters high pressure turbine (HPT) for first phase of expansion and expanded gases leaving at 4 are sent to reheat combustion chamber (reheater) for being further heated. Thus, reheating is a kind of energizing the working fluid. DEPARTMENT OF MECHANICAL ENGINEERING Assuming perfect reheating (in which temperature after reheat is same as temperature attained in first combustion chamber), the fluid leaves at state 5 and enters low pressure turbine (LPT) for remaining expansion upto desired pressure value. Generally, temperature after reheating at state 5 is less than temperature at state 3. In the absence of reheating the expansion process within similar pressure limits goes upto state 4'. Thus, reheating offers an obvious advantage of work output increase since constant pressure lines on T-S diagram diverge slightly with increasing entropy, the total work of the two stage turbine is greater than that of single expansion from state 3 to state 4'. i.e., (T3 – T4) + (T5 –T6) > (T3 – T4′). Here it may be noted that the heat addition also increases because of additional heat supplied for reheating. Therefore, despite the increase in net work due to reheating the cycle thermal efficiency would not necessarily increase. DEPARTMENT OF MECHANICAL ENGINEERING reducing compression work. It is based on the fact that for a fixed compression ratio higher is the inlet temperature higher shall be compression work requirement and vice-a-versa. Schematic for intercooled gas turbine cycle is given in Fig. 4.7. DEPARTMENT OF MECHANICAL ENGINEERING Thermodynamic processes involved in multistage intercooled compression are shown in Figs. 4.8, 4.9. First stage compression occurs in low pressure compressor (LPC) and compressed air leaving LPC at ‘2’ is sent to intercooler where temperature of compressed air is lowered down to state 3 at constant pressure. In case of perfect intercooling the temperatures at 3 and 1 are same. Intercooler is a kind of heat exchanger where heat is picked up from high temperature compressed air. The amount of compression work saved due to intercooling is obvious from p-V diagram and shown by area 2342'. Area 2342' gives the amount of work saved due to intercooling between compression. for gas turbine cycle with intercooling shows that in the absence of intercooling within same pressure limits the state at the end of compression would be 2' while with perfect intercooling this state is at 4 i.e., T2' > T4. The reduced temperature at compressor DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING Isentropic efficiency of turbine and compressor can be mathematically given as Isentropic efficiency of compressor Other factors causing the real cycle to be different from ideal cycle are as given below: Fluid velocities in turbomachines are very high and there exists substantial change in kinetic energy between inlet and outlet of each component. In the analysis carried out earlier the changes in kinetic energy have been neglected whereas for exact analysis it cannot be. (ii) In case of regenerator the compressed air cannot be heated to the temperature of gas leaving turbine as the terminal temperature difference shall always exist. (iii) Compression process shall involve work more than theoretically estimated value in order to overcome bearing and windage friction losses. Different factors described above can be accounted for by stagnation properties, compressor and turbine isentropic efficiency and polytropic efficiency. (i) DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING Solution: DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING Example 3: Solution: DEPARTMENT OF MECHANICAL ENGINEERING A heat Exchanger is not used because it would result in an exhaust temperature that would be too low for use with a high efficiency steam cycle. The Assumptions are as follows DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING Problems for practice In an air standard Otto cycle, the compression ratio is 7 and the compression begins at 35oC and 0.1 MPa. The maximum temperature of the cycle is 1100oC. Find (a) the temperature and the pressure at various points in the cycle, (b) the heat supplied per kg of air, (c) work done per kg of air, (d) the cycle efficiency and (e) the MEP of the cycle. DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING Problem 2 In a Diesel cycle, the compression ratio is 15. Compression begins at 0.1 Mpa, 40oC. The heat added is 1.675 MJ/kg. Find (a) the maximum temperature in the cycle, (b) work done per kg of air (c) the cycle efficiency (d) the temperature at the end of the isentropic expansion (e) the cutoff ratio and (f) the MEP of the cycle. DEPARTMENT OF MECHANICAL ENGINEERING Problem 3 An air-standard Ericsson cycle has an ideal regenerator. Heat is supplied at 1000°Cand heat is rejected at 20°C. If the heat added is 600 kJ/kg,find the compressor work, the turbine work, and the cycle efficiency. Since the regenerator is given as ideal, -Q2-3= Q1-4 Also in an Ericsson cycle, the heat is input during the isothermal expansion process, which is the turbine part of the cycle. Hence the turbine work is 600 kJ/kg. Problem 4 In a Braytoncycle based power plant, the air at the inlet is at 27oC, 0.1 MPa. The pressure ratio is 6.25and the maximum temperature is 800oC. DEPARTMENT OF MECHANICAL ENGINEERING Find (a) the compressor work per kg of air (b) the turbine work per kg or air (c) the heat supplied per kg of air, and (d) the cycle efficiency. DEPARTMENT OF MECHANICAL ENGINEERING DEPARTMENT OF MECHANICAL ENGINEERING INDUSTRIAL APPLICATIONS Industrial Applications The following are the applications of a gas turbine: 1. They are used to propel air-crafts and ships, 2. Gas turbine plants are used as standby plants for the hydroelectric power plants. 3. Gas turbine power plants may be used as peak loads plant and standby plants for smaller power units. 4. The shaft can be connected to other machinery to do various types of work such as: turning a helicopter rotor, running a compressor (which "crushes" a gas to a condensed form for use in industrial applications) or generating electric power. 5. The gas turbine is useful to our modern world because it is relatively compact in size and makes a lot of power. Gas turbines are used in backup power systems in Manhattan for example, when the grid goes down due to natural disaster, gas turbines power up and can produce power for emergency uses. 6. Gas turbines are used on oil platforms to make power. The oil platform is like a small city, isolated out on the water, so it requires a lot of power and does not have a lot of space. Gas turbines are also used in oil refineries to make power for the cracking process. DEPARTMENT OF MECHANICAL ENGINEERING TUTORIAL QUESTIONS UNIT – IV Theory Questions: 1. Explain about the open cycle and closed cycle turbines with neat sketches and also draw P-V & T-S diagrams. 2. State the merits of gas turbines over IC engines. 3. Draw the gas turbine power plant with inter cooling 4. List out the advantages of open cycle gas turbine over closed cycle gas turbine. 5. List different applications of gas turbine power cycles in power sector industries. 6. Discuss the relative advantages and disadvantages of gas turbines and steam turbines. 7. What are the different methods to improve the efficiency of gas turbines? 8. What are the different types of combustion chambers in gas turbine engines? Explain them in detail with relevant sketches. 9. Draw the schematic diagram of closed cycle gas turbine and explain its working. 10. Explain the operating principle of Brayton cycle with a schematic diagram p-v and T-s diagrams. 11. Why Re-heater is necessary in gas turbine? What are its effects 12. What are the requirements of a good combustion chamber for a gas turbine? 13. Explain with neat sketch the gas turbine cycles with intercooling and reheating and what will be the condition of maximum output Numerical Problems: 1. A simple gas turbine cycle works with a pressure ratio of 8. The compressor and turbine inlet temperatures are 300 K and 800 K respectively. If the volume flow rate of air is 250 m3/s, compute the power output and thermal efficiency 2. A constant pressure open cycle gas turbine plant works between temperature range of 15ºC and 700ºC and pressure ratio of 6. Find the mass of air circulating in the installation, if it develops 1100 kW. Also find the heat supplied by the heating chamber. DEPARTMENT OF MECHANICAL ENGINEERING ASSIGNMENT QUESTIONS 3. In a gas turbine plant, air is drawn at 1 bar, 150 C and the pressure ratio is 6. The expansion takes place in two turbines. The efficiency of compressor is 0.82, high pressure turbine is 0.85 and low pressure turbine is 0.84. The maximum cycle temperature is 6250 C. Calculate i) Pressure and temperature of gases entering the low pressure turbine. ii) Net power developed iii) Work ratio iv) Thermal efficiency. Work output of high pressure turbine is equal to compressor work 4. In an air standard regenerative gas turbine cycle the pressure ratio is 5. Air enters the compressor at 1 bar, 300 K and leaves at 490 K. The maximum temperature in the cycle is 1000 K. Calculate the cycle efficiency, given that the efficiency of regenerator and the adiabatic efficiency of the turbine are each 80%. Assume for air, the ratio of specific heats is 1.4. Also show the cycle on T-S diagram. 5. A gas turbine unit receives air at 1 bar and 300 K and compresses it adiabatically to 6.2 bar. The compressor efficiency is 88%. The fuel has a heating value of 44186 KJ/kg and the fuel air ratio is 0.017 KJ/kg of air. The turbine efficiency is 90 %. Calculate the work of turbine and compressor per kg of air compressed and thermal efficiency. Take Cp=1.005 KJ/kg K, γ=1.4 for the compression process, Cp=1.147 KJ/kg K, γ=1.33 for the expansion process. ASSIGNMENT QUESTIONS 1. a) Describe with neat sketches the working of a simple constant pressure open cycle gas turbine. b) Discuss the relative advantages and disadvantages of gas turbines and steam turbines. 2. Describe with neat diagram a closed cycle gas turbine and explain advantages, disadvantages and applications. 3. Explain with neat sketch the gas turbine cycles with intercooling and reheating and what will be the condition of maximum output. 4. Explain about the open cycle and closed cycle turbines with neat sketches and also draw P-V & T-S diagrams. DEPARTMENT OF MECHANICAL ENGINEERING UNIT 5 JET PROPULSION & ROCKETS Course Objective: Applications and the principles of thermodynamics to components and systems. Course Outcome: Develop problem solving skills through the application of thermodynamics. DEPARTMENT OF MECHANICAL ENGINEERING JET PROPULSION ENGINES 5.1 Introduction Je t propulsion, sim ilar to all means of propulsion, is based on Newton’s Second and Third laws of motion. The jet propulsion engine is used for the propulsion of aircraft, m issile and submarine (for vehicles operating entirely in a fluid) by the reaction of jet of gases which are discharged rearward (behind) with a high velocity. A s applied to vehicles operating entirely in a fluid, a momentum is imparted to a m ass of fluid in such a manner that the reaction of the imparted momentum furnishes a propulsive force. The magnitude of this propulsive force is termed as thrust. For efficient production of large power, fuel is burnt in an atmosphere of compressed air (combustion cham ber), the products of combustion expanding first in a gas turbine which drives the air compressor and then in a nozzle from which the thrust is derived. Paraffin is usually adopted as the fuel because of its ease of atomisation and its low freezing point. Je t propulsion w as utilized in the flying Bomb, the initial compression of the air being due to a divergent inlet duct in which a sm all increase in pressure energy was obtained at the expense of kinetic energy of the air. Because of this very limited compression, the thermal efficiency of the unit was low, although huge power was obtained. In the normal type of jet propulsion unit a considerable improvement in efficiency is obtained by fitting a turbo-com pressor which w ill give a compression ratio of at least 4 : 1 . 5.2 C lassification Je t propulsion engines are classified basically as to their method of operation as shown in fig. 5 -1 . The two main catagories of jet propulsion system s are the atmospheric Je t Propulsion Engines l Atmospheric Je t Engines (U se atmospheric air) i Turboprop or Propjet ; 1-------------- 1----------------t-----------1 Turbojet Turbojet with Ramjet Pulsejet after burner I Rockets (Use own oxidizer) r Liquid Propellant i Solid Propellant Fig. 5 - 1. Jet propulsion engines. je t engine and rocket. Atmospheric jet engines require oxygen from the atmosperic air DEPARTMENT OF MECHANICAL ENGINEERING J E T PRO PULSIO N EN G IN ES independent of the atm ospheric air. Rocket engines are discussed in art. 5-6. The turboprop, turbojet and turbojet with after burner are modified sim ple open cycle gas turbine engines. In turboprop thrust is not completely due to jet. Approximately 80 to 90 percent of the thrust in turboprop is produced by acceleration of the air outside the engine by the propeller (as in conventional aeroengines) and about 10 to 20 percent of the thrust is produced by the jet of the exhaust gases. In turbojet engine, the thrust is completely due to jet of exhaust gases. The turbojet with after burner is a turbojet engine with a reheater added to the engine so that the extended tail pipe acts as a combustion cham ber. The ramjet and pulsejet are aero-therm o-dynam ic-ducts, i.e . a straight duct type of jet engine without compressor and turbine. The ramjet has the sim plest construction of any propulsion engine, consisting essentially of an inlet diffuser, a combustion chamber and an exit nozzle of tail pipe. Since the ramjet has no com pressor, it is dependent entirely upon ram com pression. ^ */ j" Tem^rflTurf~7 ~; 0 1 2 3 V. . . 5 (bt Pressure,Velocity ond temperature distribution Fig. 5 - 2 Turbojet engine. The pulsejet is an intermittent combustion jet engine and it operates on a to a reciprocating engine and may be better compared with an ideal Otto than the Joule or Bryton cycle. From construction point of view, it is some to a ramjet engine. The difference lies in provision of a mechanical valve to prevent the hot gases of combustion from going out through the diffuser. cycle sim ilar cycle rather what sim ilar arrangement 5.3 Turbojet Engine The turboject engine (fig ..5-2) is sim ilar to the sim ple open cycle constant pressure gas turbine plant (fig. 4-2) except that the exhaust gases are first partially expanded in DEPARTMENT OF MECHANICAL ENGINEERING I leaving the turbine are then expanded to atmospheric pressure in a propelling (discharge) nozzle. The remaining energy of gases after leaving the turbine is used as a high speed jet from which the thrust is obtained for forward movement of the aircraft. Thus, the essential components of a turbojet engine are : . . An entrance air diffuser (diverging duct) in front of the com pressor, which causes rise in pressure in the entering air by slowing it down. This is known as ram. The pressure at entrance to the compressor is about 1-25 tim es the ambient pressure. . . A rotary com pressor, which raises the pressure of air further to required value and delivers to the combustion cham ber. The compressor is the radial or axial type and is driven by the turbine. . . The combustion cham ber, in which paraffin (kerosene) is sprayed, as a result of this combustion takes place at constant pressure and the temperature of air is raised. . . The gas turbine into which products of combustion pass on leaving the combustion cham ber. The products of combustion are partially expanded in the turbine to provide necessary power to drive the com pressor. . . The discharge nozzle in which expansion of gases is completed, thus developing the forward thrust. A Rolls-Ro yce Derwent jet engine employs a centrifugal compressor and turbine of the im pulse-reaction type. The unit has 550 kg m ass. The speed attained is 960 km/hour. 5.3.1 W orking C ycle : Air from surrounding atmosphere is drawn in through the diffuser, in which air is com pressed partially by ram effect. Then air enters the rotary compressor and major part of the pressure rise is accomplished here. The air is compressed to a pressure of .about 4 atm ospheres. From the compressor the air passes into the annular combustion cham ber. The fuel is forced by the oil pump through the fuel nozzle into the combustion cham ber. Here the fuel is burnt at constant pressure. This raises the temperature and volume of the mixture of air and products of combustion. The m ass of air supplied is about 60 times the m ass of the fuel burnt. This excess air produces sufficient m ass for the propulsionjet, and at the sam e time prevents g as tem perature from reaching values which are too high for the metal of the rotor blades. The hot gases from the combustion chamber then pass through the turbine nozzle ring. The hot gases which partially expand in the turbine are then exhausted through the discharge (propelling nozzle) by which the remaining enthalpy is converted into kinetic energy. Thus, a high ve lo city propulsion jet is produced. The oil pump ad compressor are mounted on the sam e shaft as the Entropy turbine rotor. The power developed DEPARTMENT OF MECHANICAL ENGINEERING J E T PRO PULSIO N EN G IN ES Som e starting devicd such as com pressed air motor or electric motor, must be provided in the turbojet plant. Flight speeds upto 800 km per hour are obtained from this type of unit. The basic thermodynamic cycle for the turbojet engine is the Jo ule or Brayton cycle as shown in T - <t> diagram of fig. 5 -3 . W hile drawing this cycle, following sim plifying assum ptions are made : - There are no pressure losses in combustion chamber. Specific heat of working medium is constant. Diffuser has ram efficiency of 100 percent i.e ., the entering atm ospheric air is diffused isentropically from velocity V0 to zero (V0 is the vehicle velocity through the air). - Hot gases leaving the turbine are expanded isentropically in the exit nozzle i.e ., the efficiency of the exit nozzle is 100 percent. 5.3.2 T h ru st Pow er and P ro p u lsive E fficie n c y : The jet aircraft draws in air and expels it to the rear at a markedly increased velocity. The action of accelerating the m ass of fluid in a given direction creates a reaction in the opposite direction in the form of a propulsive force. The magnitude of this propulsive force is defined as thrust. It is dependent upon the rate of change of momentum of the working medium i.e . air, as it passes through the engine. The basis for comparison of jet engines is the thrust. The thrust, T of a turbojet engine can be expressed as, T * m (V j - Vo) ...( 5 .1 ) where, m - m ass flow rate of gases, kg/sec., Vj = exit jet velocity, m /sec., and, Vo = vehicle velocity, m/sec. The above equation is based upon the assumption that the m ass of fuel is neglected. Since the atmospheric air is assum ed to be at rest, the velocity of the air entering relative to the engine, is the velocity of the vehicle, Vo. The thrust can be increased by increasing the m ass flow rate of gas or increasing the velocity of the exhaust jet for given Vo. Thrust power is the time rate of development of the useful work achieved by the engine and it is obtained by the product of the thrust and the flight velocity of the vehicle. Thus, thrust power T P is given by /./ N-m ...( 5 .2 ) TP = T V0 = m(Vj - V0) Vo — The kinetic energy imparted to the fluid or the energy required to change the momentum of the m ass flow of air, is the difference between the rate of kinetic energy of entering air and the rate of kinetic energy of the exist gases and is called propulsive power. The propulsive power PP is given by p p = !'!m (AYVJj 2 -—lV°_o22) N.m/sec. •f5 ,3 ) Propulsive efficiency is defined 'as the ratio of thrust power ( TP) and propulsive power (PP) and is the m easure of the effectiveness with which the kinetic energy imparted to the fluid is transformed or converted into useful work. Thus, propulsive efficiency r\p is given by TP m{Vi - VQ) V0 2 DEPARTMENT OF MECHANICAL ENGINEERING ELEM EN TS O F H EAT EN G IN ES Vol. Ill 2 ( V j- Vp) V0 " * = 2 2V0 ...( 5 .4 ) = v j+ v0 m 1 ^ V j2 - v02 From the expression of rip it may be seen that the propulsion system approaches maximum efficiency as the velocity of the vehicle approaches the velocity of the exhaust gases. But as this occurs, the thrust and the thrust power approach zero. Thus, the ratio of velocities for maximum propulsive efficiency and for maximum power are not the sam e. Alternatively, the propulsive efficiency can be expressed as TP TP . . . (5.5) 11p ~ P P = TP + K .E . losses Therm al efficiency of a propulsion is an indication of the degree of utilization of energy in fuel (heat supplied) in accelerating the fluid flow and is defined as the increase in the kinetic energy of the fluid (propulsive power) and the heat supplied. Thus, . Propulsive power r Therm al efficie ncy, ti t » - r r ^ i Heat supplied 1 11 ________ Propulsive power . . . (5.6) Fuel flow rate x C .V . of fuel The overall efficiency is the ratio of the thrust power and the heat supplied. Thus, overall efficiency is the product of propulsive efficiency and thermal efficiency. The propulsive and overall efficiencies of the turboject engine are comparable to the m echanical efficiency and brake thermal efficiency respectively, of the reciprocating engine. Problem - 1 : A je t propulsion unit, with turbojet engine, having a forward speed of 1,100 km/hr produces 14 kN o f thrust and u ses 40 kg of air per second. Find: (a) the relative exist je t velocity, (b) the thrust power, (c) the propulsive power, and (d) the propulsive efficiency. (a) Forward speed, VQ = = 305 55 rc^se c - Using eqn. (5 .1 ), thrust, T = m(Vj - \/0) i.e., 14,000 = 40 (Vj - 305-55) Vi = 14,0°°- + 305-55 = 350 + 305-55 = 655-55 nrVsec. I 40 Thus relative exist jet velocity, Vj = 655-55 m /sec. (b) Using eqn. (5.2) Thrust power, TP - T x VQ 3 = 14,000 x 305-55 = 42,77,700 N.m/sec. or = 4,277.7 kN .m /sec. (c) Using eqn. (5.3), Propulsive power, P P = m (V22 - V02) 40[(655-55) - (305-55)' = 6,727 x 103 N.m/sec = 6,727 KN.m/sec or 6,727 kW DEPARTMENT OF MECHANICAL ENGINEERING J E T PRO PULSIO N EN G IN ES Propulsive efficiency, r|P = 1 + ^655-55'j 1 + 1305-55 = 0-636 i.e ., 63.6% 5.4 Ram Je t A french engineer, Rane Lorin invented and patented the first ram jet in 1913. It w as not until the advent of the high speed wind tunnel, however, that the U .S . Navy sponsored research team developed a workable ram jet at Johns Hopkins University. The Ram jet w as referred to in the past as athodyd (aerothermodynamic duct), Lorin tube or flying stovepipe. It is a steady combustion or continuous flow engine. It has the sim plest construction of any propulsion eng in e (fig . 5 -4 ) c o n sistin g essentially of an inlet diffuser, a combustion cham ber, and an exit nozzle or tailpipe. Since the ram jet has no compressor,'■it is dependent entirely upon ram com pression. Ram compression is the transformation of the kinetic energy of the entering air into pressure energy. Fig. 5-5 shows variation of ratio P j/P 0 with the Mach number* of vehicle. The pressure ratio increases as Mach number is increased. The ram jet pressure ratio increases very slowly in the subsonic speed range. Thus, the ram jet must be boosted up to a speed over 500 km/hr by a suitable means such as a turbojet or a rocket, before the ram jet will produce any thrust and must be boosted to even higher speeds before the thrust produced exceeds the drag. From fig. 5-5 it may be noted that the ram acts in effect like a com pressor. At a Mach number* of 2-0, it is found that the ideal ram pressure is 8-0. At this high Mach number, it becomes economical to go to the ram jet engine and do away with the m echanical compressor and turbine wheels. After the ram jet is boosted, the- velocity of the air entering the Jiffuser is decreased and is accompanied by an increase in pressure. This creates a pressure barrier at the after end of the diffuser. The fuel that is sprayed into the combustion chamber through injection nozzles is mixed with the air and ingited by means of a spark plug. The expansion of the gases toward the diffuser entrance is restricted by the pressure barrier at the after end of the diffuser; consequently, the gases are constrained to expand through the tail pipe and out through the exit nozzl DEPARTMENT OF MECHANICAL ENGINEERING is not effective and that there are pulsations created in the combustion chamber which affect the air flow in front of the diffuser. Since the ram jet engine has no turbine, the temperature of the gases of combustion is not lim ited to a relatively low figure as in the turbojet engine. Air fuel ratios of around 15*1 are used. This produces exhaust temperatures in the range of 2000°C to 2200°C. Extensive research is being conducted on the development of hydrocarbon fuels that will give 30 percent more energy per unit volume than current aviation gasolines. Investigations are carried Out to determine the possibility of using, solid fuels in the ram jet and in the after burner of the turbojet engine. If powdered aluminium could be utilized Moch number — •as an aircraft fuel, it would deliver over 2-5 tim es as much heat per . unit volume as aviation gasoline, Fig. 5 - 5 . Ram pressure ratio versus Mach number of while some other could deliver vehicle for sea level condition. almost four tim es as much heat. The tem perature, pressure and velocity of the air during its passage through a ram jet engine at supersonic flight are shown in fig. 5M . The cycle for an ideal ram jet, which has an isentropic entrance diffuser and exit nozzle, is the Joule cycle as shown by the dotted lines in fig. 5 -6 . The difference between the actual and ideal jet is due principally to losses actually encountered in the flow system . The sources of these losses are : . . . W all friction and flow separation in the subsonic diffuser and shock in the supersonic diffuser. . . Obstruction of the air stream by the burners which introduces eddy currents and turbulence in the air stream . . . Turbulence and eddy currents introduced in the flow during burning. Fig. 5 -6 . T - <t> diagram of Ram jet engine. . . W all friction in the exit nozzle. By far, the most critical component of the <ram jet is the diffuser. Due to the peculiarities DEPARTMENT OF MECHANICAL ENGINEERING efficient at a given speed may be quite inadequate at another velocity. Because of the sim plicity of the engine, the ram jet develops greater thrust per unit engine weight than any other propulsion engine at supersonic speed with the exception of the rocket engine. The thrust per unit frontal area increases both with the efficiency and the air flow through the engine; therefore much greater thrust per unit area is obtainable at high supersonic speeds. General performance of a ram jet engine in the subsonic range would have a specific fuel consumption between 0.6 to 0*8 kg fuel per N thrust - hr and a specific weight between 0*01 to 0*02 kg per N thrust. The supersonic ram jet engine has a specific fuel consumption between 0*25 to 0-04 and a specific weight between 0-01 to 0-04. Thus, the best performance of the ram jet engine is obtained at flights speeds of 1500 to 3500 km/hr. 5.5 Pulse Jet Engine The pulse jet engine is somewhat sim ilar to a ram jet engine. The difference is that a m echanical valve arrangement is used to prevent the hot gases of combustion from flowing out through the diffuser in the pulse jet engine. Paul Schm idt patented principles of the pulse jet engine in 1930. It was developed by Germ any during W orld-W ar-ll, and was used as the power plant for “buzz bomb". The turbojet and ram jet engines are continuous in operation and are based on the constant pressure heat addition (Bryton) cycle. The pulse jet is an intermittent combusion engine and it operates on a cycle sim ilar to a reciprocating engine and may be better compared with an ideal Otto cycle rather than the Joule or Bryton cycle. The com pression of incoming air is accomplished in a diffuser. The air passes through the spring valves and is mixed with fuel from a fuel spray located behind the valves. A spark plug is used to initiate combustion but once the engine is operating normally, the spark is turned off and residual flam e in the combustion chamber is used for ignition, lin e engine w alls also may get hot enough to initiate combustion. The m echanical valves which were forced open by the entering air, are forced shut when the combustion process raises the pressure within the engine above the pressure in the diffuser. As the combustion products cannot expand forward, they move to the rear at high velocity. The combustion products cannot expand forward, they move to the rear at high velocity. When the combustion produ-pf~ leave, the pressure in the combustion chamber drops and the high pressure air in the c.flbser Tbrces the valves open and fresh air enters the engine. Since the products of combustion leave at a high velocity there is certain scavenging of the engine caused by the decrease in pressure occasioned by the exit gases. There is a stable cycle set up in which alternate waves of high and low pressure travel down the engine. The alternating cycles of combustion, exhaust, induction, combustion, etc. are related to the acoustical velocity at the temperature prevailing in the engine. Since the temperature varies continually, the actual process is*complicated, but a workable assumption is that the tube is acting sim ilar to a quarter wave length organ pipe. The series of pressure and rarefaction waves move down it at the speed of sound for an assum ed average tem peratures. The frequency of the combustion cycle may be calculated from the following expression: ^ = 4 l cvc*es/secwhere, a = V fTTT = sound velocity in the medium at temperature, T, and L = length of engine ( from valves to exit). DEPARTMENT OF MECHANICAL ENGINEERING A serious limitation placed upon pulse jet engine is the m echanical valve arrangement. Unfortunately, the valves used have resonant frequencies of their own, and under certain conditions, the valve will be forced into resonant vibration and w ill be operating when they should be shutting. Th is limitation of valves also lim its the engine because the gas goes out of the diffuser when it should go out of the tail pipe. Despite the apparent noise and the valve limitation, pulse jet engines have several advantages when compared to other thermal jet engines. . . The pluse jet is very inexpensive when compared to a turbojet. . . The pulse jet produces static thrust and produces thrust in excess of drag at much lower speed than a ram jet. . . The potential of the pulse jet is quite considerable and its development and research may well bring about a wide range of application. 5.6 Rocket M otors The jet propulsion action of the rocket has been recognised for long. Since the early beginning, the use of rockets has been in war time as a weapon and in peace time as a signaling or pyrotechnic displays. Although, the rocket was employed only to an insignificant extent in World W ar-I, marked advances were made by the research that w as undertaken at that time. In . World W ar-II, the rocket became a major offensive weapon employed by all warring powers. Rockets and rocket powered weapons have advanced to a point where they are used effectively in military operations. Rocket type engine differs from the atmospheric jet engine in that the entire m ass of the jet is generated from the propellant carried within the engine i.e . the rocket motor carries both the fuel and the oxidizing agent. A s a result, this type of engine is independent of the atm ospheric air that other thermal jet engines must rely upon. From this point of view rocket motors are most attractive. There are, however, other operational features that make rocket less useful. Here, the fundamentals of rocket motor theory and its applications are discussed. Rocket engines are classified as to the type of propellant used in them. Accordingly, there are two major groups: One type belonging to the group that utilizes liquid type propellants and other group that uses solid type propellants. The basic theory governing the operation of rocket motor is applied, equally to both the liquid and the solid propellant rocket. Rocket propulsion, at this tim e, would not be regarded as a competitor of existing means for propelling airplanes, but as a source of power for reaching objectives unattainable by other methods. The rocket motors are under active development programmes for an increasing number of applications. Some of these applications are : - Artillery barrage rockets, AntM ank rockets, All types of guided m issiles, v Aircraft launched rockets, Jets assisted take-off for airplanes, Engines for long range, high speed guided m issiles and pilotless aircrafts, and M ain'and auxiliary propulsion engines on transonic airplanes. DEPARTMENT OF MECHANICAL ENGINEERING J E T PRO PULSIO N EN G IN ES .carried within the engine. Therefore, it is not dependent on the atm ospheric air to furnish the oxygen for combustion. However, since the rocket carries its own oxidiser, the propellant consumption is very high. The particular advantages of the rocket are : . . Its thrust is practically independent of its environments. . . It requires no atmospheric oxygen for its operation. . . It can function even in a vacuum . . . Itappear to be the sim plest means for converting the themochemical .energy of a propellant combination (fuel plus oxidizer) into kinetic energy associated with a jet flow gases. Despite its apparent sim plicity, the development of a reliable rocket system must be light in weight and the rocket motor must be capable of sustained operation in contact with gases at temperature above 2800° C and at appreciable pressures.The -problem of m aterials in consequently a major one. Furthermore, owing to the enormous energy releases involved, problem of ignition, smooth start up, thrust control, cooling etc. arise. A major problem of development of rocket is selection of suitable propellant to give maximum energy per premium total weight (propellant plus containing vessels) and convenience factors such as a safety in handling, dependability, corrosive tendencies, cost; availability and storage problems. In general, it can be stated that there is a wide variety of fuels that are satisfactory for rocket purpose, but choice of oxidizers is at present distinctly limited. 5.6.1 B a sic Theo ry : Figure 5-7 shows a schem atic diagramof a liquid bi-propellant rocket engine. It consists of an injection system , a combustioncham ber, and an exit nozzle. The oxidizer and fuel burnt, in the combustion chamber produces a high pressure. The pressure produced is governed by - M ass rate of flow of the propellants, - Chem icals characteristics of the propellants, and - Cross-section area of the nozzle throat. The gases are ejected to the atmosphere at supersonic speeds through the nozzle. The enthalpy of high pressure gases is converted into kinetic energy. The reaction to the ejection of the high velocity, produces the thrust on the rocket engine. Combustion chamber Fig. 5 - 7 . N ozzle Schematic diagram of a liquid bi-propellant uncooled rocket motor. The thrust developed is a resultant of the pressure forces acting upon the inner and the outer surface of the rocket engine. The resultant internal force acting on the engine is given by DEPARTMENT OF MECHANICAL ENGINEERING where, mp = M ass rate of propellant consumption, kg/sec, Vj = Je t velocity relative to nozzle, m/sec, V„t = Average value of the x-component of the velocity of gases crossing, Aj, Pj = Exist static pressure, N/m2, and Aj = Exit area of nozzle, m2. The resultant external forces acting on the rocket engine are PoA» where pQ is the atm ospheric pressure in N/m2. The thrust which is a resultant of the total pressure forces becomes T - mP Vxj + Aj(P j - P J N . > . (5.8) Let Vj = the exit velocity of the rocket gases, assumed constant and let VXj = X Vj. Then, eqn. (5.8) becomes 7 - \ m p Vj + A j{p j - p J N ...(5 .9 ) The coefficient A. is the correction factor for the divergence angle a of the exit conical section of the nozzle. \ is given by ^ 1 cos 2 ct 1 /^ \ /p \ =— = —(1 + cos a ) . . . (5.10) 4 (1. - cos a ) 2 ' Equation (5.8) shows that thrust of a rocket engine increases a s the atmospheric pressure decreases. Therefore, maximum thrust will be obtained when PQ= 0, i.e ., rocket engine produces maximum thrust when operating in a vacuum. In testing a rocket engine, thrust and propellant consumption for a given time are readily m easured. It is convenient then, to express the thrust in term s of the m ass rate of flow of propellant and an effective jet velocity, Vej i.e ., Thrust, T = mp x Vej . . . , (5.11) The effective je t exit velocity is a hypothetical velocity and for convenience in test work it is defined from eqns. (5.9) and (5.11) as under : Vej “ k vj + 7^ (P j ~ Po> ’ r ts e 0 - * • (5,12) The effective jet exit velocity has become an important parameter in rocket motor performance. The thrust power, TP developed by a rocket motor is defined as the thrust multiplied by the flight velocity, VQ. TP - T V Q = mp - V9 j- VQ N.m/sec. • • . (5.13) The propulsive efficiency, r\p is the ratio of the thrust power to propulsive power supplied. The propulsive power is the thrust power plus the kinetic energy lost in the exhaust, i.e., K .E . Loss = ^ mp (Vej - v f N.m/sec. Therefore, the propulsive efficiency may be expressed as __________ TP ip - T P * K .E . Loss ' mp V^Vc Vej Vo_ mp ( V j - v f mp DEPARTMENT OF MECHANICAL ENGINEERING I JET p r o p u l s io n 193 e n g in e s 2(V o/V ej) np . . . (5.14) 1 + ( Vq / Vej f Specific Impulse, lsp has become an important parameter in rocket motor performance and is defined as the thrust produced per unit m ass rate of propellant consumption. mn • V,ej = V,ej , m, • • • <5 1 5 > 3 Specific impulse, with the units, Newtons of thrust produced per kg of propellant burned per second, gives a direct comparison as to the effectiveness among propellants. It is desirable to use propellants with the greatest possible specific im pulse, since, this allows a greater useful load to be carried for a given overall rocket weight. 5.6.2. T yp es of Rocket M otors : The propellant employed in a rocket motor may be a solid, two liquids (fuel plus oxidizer), or m aterials containing an adequate supply of available oxygen in their chem ical composition (monopropellant). Solid propellants are used for rockets which are to operate for relatively short periods, upto possibly 45 seconds. Their main application is to projectiles, guided m issiles, and the assisted take-off aircraft. Combustion chamber Burns on end surface only N ozzle (a) Restricted burning Propellant charge Ends prevented from burning by w ashers Nozzle ( b) Unrestricted burning ” Fig. 5 - 8 Burns on outside and inside cylindrical surfaces Schematic diagram of a solid propellant rocket. .. Solid propellant rockets (fig. 5-8) have been of two basic types : . . Unrestricted burning types for projectiles and launching rockets; and . . Restricted burning types for assisted take-off of aircraft and for propelling m issiles. In the unrestricted burning rocket [fig. 5-8(a)] all surfaces of the propellant grain except the ends are ignited; in restricted burning rockets [fig. 5-8(b)] onlyone surface of the propellant is permitted toburn. Liquid propellant rockets utilizes liquidpropellants which are stored in the containers outside the combustion chamber. The basic theory of operation of this type of rocket is sam e as that for solid propellant rocket. Liquid propellant rockets were developed in order to overcome some of the undesirable features of the DEPARTMENT OF MECHANICAL ENGINEERING li solid propellant rockets such as short duration of thrust, and no provisions for adequate cooling or control of the burning after combustion starts. Here, the propellant in the liquid Fig. 5 - 9 . Schematic diagrams of bi-propellant rocket system. state is injected into a combustion chamber, burned and exhausted at a high velocity through the nozzle. The liquid propellant is also used to cool the rocket motor by circulation of fuels around the w alls of the combustion chamber and around the nozzle. Certain liquid fuel, however, such as hydrogen peroxide, burn at such temperatures that no cooling is necessary. Figure 5-9 shows schem atic diagrams of pressure feed and pump feed liquid bipropellant rocket system s. Problem -2 : The effective exit je t velocity of a rocket is 3000 m/sec, the forward flight velocity is 1500 m/sec and the propellant consumption is 70 kg per sec. Calculate : (a) Thrust, (b) Thrust power, (c) Specific impulse, (d) Specific propellant consumption, and (e) Propulsive efficiency o f the rocket. (a) Using eqn. (5.11), Thrust, T = mp x Vej = 70 x 3,000 = 2,10,000 N or 210 kN (b) Using eqn. (5.13), DEPARTMENT OF MECHANICAL ENGINEERING J E T PRO PULSIO N EN G IN ES (c) Using eqn. (5.14), Specific impluse, lsp = ~ = •p 'V Vei «= vej = mp (d) Specific propellant consumption - mp T 3,000 N.s/kg mp mp Vej 1 Vej 3,000 = 3-3 x 10-4 kg/N.s (e) Using eqn. (5.14), Propulsive efficiency, r\p = — 2 (K /V e /)__ 1 ♦ (V o /v y 2 2(1500/3000) 1 + (1500/3000) = 0-8 i.e ., 80% DEPARTMENT OF MECHANICAL ENGINEERING engines to power air planes, as we know them today, is not feasible because of their high fuel consumption. Also, the use of ram jet engines is not economical at lower than 1500 km/hr vehicle speeds. Rocket Cft Ej 60 I— V w 5 « 8 60 c OJ o w 0) 0. Supercharged reciprocating engine with mpenelliieerr \l n pro \ "v N, ' ^ Unsupercharged reciprocating — engine with propeller 6 a t k® /1 Figure 5-11 shows variation of thrust with altitude for different propulsion systerns. It may be noted that the thrust ’ of rocket motor increases with altitude while the thrust of other types of vehicles decreases with altitude. Relative air densit 12 Altitude km> Fig. 5-11 Variation of thrust with altitude for different propulsion systems. Figure 5-12 gives relative picture of the probable operating envelope of the various propulsion system s. 0? DEPARTMENT OF MECHANICAL ENGINEERING 10 erformance for various propulsion engine. INDUSTRIAL APPLICATIONS INDUSTRIAL APPLICATIONS Rocket applications 1. Satellites in space serve air communication 2. Spacecraft 3. Missiles 4. Jet assisted air planes 5. Pilotless aircraft DEPARTMENT OF MECHANICAL ENGINEERING TUTORIAL QUESTIONS Theory Questions: 1. What are the different rocket propulsion systems? Brief the working differences between the propeller-jet, turbojet and turbo-prop. 2. With a neat diagram explain the working of rocket engine 3. Describe briefly about thrust augmentation method used in propulsion. 4. With a neat sketch, explain the working of turbo jet engine. 5. Differentiate between solid propellant and liquid propellant rocket engines. 6. What are the applications of pulse jet engines 7. Give the difference between ramjet and pulse jet engines 8. What are composite and homogeneous solid propellants? How do they work? State their merits and demerits. 9. What is the essential difference between rocket propulsion and turbo-jet propulsion? 10. Write a detailed classification of rockets. Explain liquid propellant rocket with a neat sketch Define and explain the terms: i. Thrust ii. Thrust power, iii. Effective jet exit velocity, iv. Propulsive efficiency related to turbojet engines. 11. What are the various applications of rockets? 12. Explain the advantages and disadvantages of bipropellants used in rocket engines over monopropellants. 2. Derive expressions for the thrust and propulsion efficiency of rockets and compare with those of turbojet Numerical Problems: 1. A jet propulsion system has to create a thrust of 100 tones to move the system at a velocity of 700 km/hr. If the gas flow rate through the system is restricted to a maximum of 30 kg/s. find the exit gas velocity and propulsive efficiency. DEPARTMENT OF MECHANICAL ENGINEERING 2. In a jet propulsion unit, initial pressure and temperature to the compressor are 1.0 bar and 100C. The speed of the unit is 200m/s. The pressure and temperature of the gases before entering the turbine are 7500 C and 3 bar. Isentropic efficiencies of compressor and turbine are 85% and 80%. The static back pressure of the nozzle is 0.5 bar and efficiency of the nozzle is 90%. Determine (a) Power consumed by compressor per kg of air. (b)Air-fuel ratio if calorific value of fuel is 35,000 kJ/kg. Cp of gases=1.12 kJ/kg K, _ =1.32 for gases. 3. A turbo-jet engine flying at a speed of 960 km/h consumes air at the rate of 54.5 kg/s. calculate i). Exit velocity of the jet when the enthalpy change for the nozzle is 200 KJ/kg and velocity coefficient is 0.97. ii).fuel flow rate in kg/s when air fuel ratio is 75:1 iii). Thrust specific fuel consumption iv). Propulsive power v). Propulsive efficiency. 4. A simple turbine jet unit was tested when stationary and the ambient conditions were 1bar and 150C. The pressure ratio for the compressor was 4:1. A fuel consumption of 0.37kg/s was obtained for an air flow of 23kg/s. Calculate the thrust produced if the exhaust gases from the turbine were expanded to atmospheric pressure in a convergent nozzle. Assume the following data: Isentropic efficiency of compressor-80% Isentropic efficiency of turbine-85% Efficiency of nozzle-93% Transmission efficiency-98% Calorific value of fuel-42000kJ/kg Assuming working fluid to be air throughout. 5. In a turbojet, air is compressed in an axial compressor at inlet conditions of 1 bar and 1000C 3.5 bar. The final temperature is 1.25 times that for isentropic compression. The temperature of gases at inlet to turbine is 4800C. The exhaust gases from turbine are expanded in a velocity of approach is negligible and expansion may be taken to be isentropic in both turbine and nozzle. Value of gas constant R and index r are same for air and flue gases. Determine i) Power required to drive the compressor per kg of air/sec ii) Air-fuel ratio if the calorific value of fuel is 42,000 kJ/kg iii) Thrust developed / kg of air / sec. DEPARTMENT OF MECHANICAL ENGINEERING ASSIGNMENT QUESTIONS ASSIGNMENT QUESTIONS 1. Why is thrust augmentation necessary? What are the methods for thrust augmentation in a turbojet engine? 2. A turbo-jet engine flying at a speed of 960 km/h consumes air at the rate of 54.5 kg/s. calculate i). Exit velocity of the jet when the enthalpy change for the nozzle is 200 KJ/kg and velocity coefficient is 0.97. ii).fuel flow rate in kg/s when air fuel ratio is 75:1 iii). Thrust specific fuel consumption iv). Propulsive power v). Propulsive efficiency. 3. With a neat diagram explain the working of rocket engine 4. What is turbine and classify them? DEPARTMENT OF MECHANICAL ENGINEERING PREVIOUS QUESTION PAPERS Code No: R15A0313 R15 MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) III B.Tech I Semester Regular/supplementary Examinations, November 2018 Advanced Thermal Engineering (ME) Roll No Time: 3 hours Max. Marks: 75 Note: This question paper contains two parts A and B Part A is compulsory which carriers 25 marks and Answer all questions. Part B Consists of 5 SECTIONS (One SECTION for each UNIT). Answer FIVE Questions, Choosing ONE Question from each SECTION and each Question carries 10 marks. Note: Steam tables are allowed. ****** PART-A (25 Marks) 1). a b c d e f g h i j 2 3 4 5 Draw the line diagram of a Rankine cycle and mention the various components State the advantages of regenerative cycle over simple Rankine cycle. [2M] [3M] State the differences between fire tube and water tube boilers [2M] What is the function of a safety valve? [3M] Mention any two differences between jet and the surface condenser [2M] Write the advantages and disadvantages of steam turbines [3M] What do you mean by the term gas turbine? [2M] State the merits of gas turbines over IC engines. [3M] Draw the gas turbine power plant with inter cooling [2M] What is thrust augmentation [3M] PART-B (50 MARKS) SECTION-I Explain a regenerative cycle with a diagram and derive the expression for its [10M] thermal efficiency. OR In a Rankinne cycle the steam at inlet to turbine is saturated at a pressure of 35 bar [10M] and exhaust pressure is at 0.2 bar. Determine i) the pump work ii) the turbine work iii) Rankine efficiency iv) the condenser heat flow v) the dryness at the end of expansion. SECTION-II a) Explain any two of the following with neat sketches (5M) [10M] i) Super heater ii) Air Preheater iii) Economizer b) List the advantages of high pressure boilers (5M) OR a) Steam having pressure of 10.5 bar and 0.95 dryness fraction is expanded [10M] through a convergent- divergent nozzle and the pressure of steam leaving the nozzle is 0.85 bar. Find the velocity at the throat for maximum discharge Page 1 of 2 condition. If the index of expansion may be assumed to be 1.135, calculate the mass flow rate of steam through the nozzle. (5M) b) Explain any two of the following with sketches i) pressure gauge ii) water level gauge iii) feed check valve iv) high steam and low water safety valve. (5M) 6 7 8 9 10 SECTION-III What are the compounding methods used in reducing the speed of the turbine rotor? Explain any two methods. OR A single stage steam turbine is supplied with steam at 5 bar, 200 oC at the rate of 50 kg/min. It expands into a condenser at a pressure of 0.2 bar. The blade speed is 400 m/s. The nozzles are inclined at an angle of 20 degree to the plane of the wheel and outlet blade angle is 30 degrees. Neglecting friction losses calculate i) power developed ii) blade efficiency and iii) stage efficiency. SECTION-IV a) Describe with neat sketches the working of a simple constant pressure open cycle gas turbine.(5M) b) Discuss briefly the methods employed for improvement of thermal efficiency of open cycle gas turbine plant. (5M) OR A gas turbine unit has a pressure ratio of 6:1 and maximum cycle temperature of 610 oC. The isentropic efficiencies of the compressor and turbine are 0.80 and 0.82 respectively. Calculate the power output in kW of an electrical generator geared to the turbine when the air enters the compressor at 15 oC at the rate of 16 kg/sec. Take Cp as 1.005 kJ/kgK. γ=1.4 for the compression process and take Cp= 1.11 kJ/kgK and γ =1.333 for the expansion process. SECTION-V a) Explain the working difference between propeller -jet, turbo-jet and turbo- prop. (5M) b) State the fundamental differences between jet propulsion and rocket propulsion. (5M) OR 11(a) With a neat diagram explain the working of rocket engine (b) Describe briefly about thrust augmentation method used in propulsion. [10M] [10M] [10M] [10M] [10M] [5M] [5M] Page 2 of 2 R15 Code No: R15A0313 MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) III B.Tech I Semester Supplementary Examinations, May 2019 Advanced Thermal Engineering (ME) Roll No Time: 3 hours Max. Marks: 75 Note: This question paper contains two parts A and B Part A is compulsory which carriers 25 marks and Answer all questions. Part B Consists of 5 SECTIONS (One SECTION for each UNIT). Answer FIVE Questions, Choosing ONE Question from each SECTION and each Question carries 10 marks. 1). a b c d e f g h i j 2 3 4 PART-A (25 Marks) State the methods of increasing the thermal efficiency of a Rankine cycle. Draw the PV diagram of a Rankine cycle and mention the different processes. [2M] [3M] Write the differences between forced circulation and free circulation boilers [2M] What is the function of boiler mountings? Can a boiler work without mountings? [3M] Define a steam condenser [2M] What do you understand by diagram efficiency in case of steam turbine [3M] How are gas turbines classified? [2M] State the merits of gas turbines over steam turbines. [3M] Mention the different operating variables that affect the efficiency of a gas turbine [2M] plant. What are the applications of pulse jet engines? [3M] PART-B (50 MARKS) SECTION-I a) In a steam power cycle, the steam supply is at 15 bar and dry and saturated. The [5M] condenser pressure is 0.4 bar. Calculate the Rankine and Carnot efficiencies of the cycle. Neglect the pump work. .b) Draw the block diagram of reheat cycle by representing all the components and [5M] explain the salient features of the cycle. OR A reheat Rankine cycle operates between the pressure limits of 26 bar and [10M] 0.04 bar. The steam entering the HP turbine and LP turbine has a temperature of 400 oC. The steam leaves the HP turbine as dry saturated. Compare thermal efficiency and steam rate of Rankine cycle without and with reheating. Neglect the feed pump work. SECTION-II a) Steam is expanded in a set of nozzles from 10 bar and 200 OC to 5 bar. [5M] Neglecting the initial velocity, find the maximum area of the nozzle required to allow a flow of 3 kg/s under the given conditions. Assume that the expansion of Page 1 of 2 the steam to be isentropic. Also name the type of nozzle. b) Clearly explain about any one type of high pressure boiler OR 5 Dry saturated steam enters a steam nozzle at a pressure of 15 bar and is discharged at a pressure of 2 bar. If the dryness fraction of discharge steam is 0.96, what will be the final velocity of steam? Neglect the initial velocity of the steam. If 10% of the heat drop is lost in friction, find the percentage reduction in the final velocity. SECTION-III 6 Derive the expression for maximum blade efficiency of a single stage impulse turbine. OR 7 Define the following as related to steam turbines. i) a) i) Blade Speed ratio ii) blade velocity coefficient iii) diagram efficiency iv) stage efficiency ii) B) explain the difference between an impulse turbine and a reaction turbine SECTION-IV 8 Describe with neat diagram a closed cycle gas turbine and explain advantages, disadvantages and applications. OR 9 A gas turbine unit receives air at 1 bar and 300 K and compresses it adiabatically to 6.2 bar. The compressor efficiency is 88%. The fuel has heating value of 44186 kJ/kg and the fuel air ratio is 0.017 kJ/kg of air. The turbine internal efficiency is 90%. Calculate the work of turbine and compressor per kg of air compressed and thermal efficiency for products of combustion, Cp =1.147 kJ/kgK and ᵞ =1.333. SECTION-V 10 a) Derive the equation for thrust, thrust power of a jet propulsion. b) The following data pertain to a turbojet flying at a altitude of 9500 m: speed of the turbojet is 800 km/hr, propulsive efficiency=55% overall efficiency of a turbine plant is 17%. Density of air at 9500 m altitude is 0.17kg/m3. Drag on the plane is 6100 N, assuming calorific value of the fuel used as 46000 kJ/kg. Calculate : i) absolute velocity of the jet ii) Volume of air compressed /min. OR 11 a) With a neat sketch, explain the working of turbo jet engine. b) Differentiate between solid propellant and liquid propellant rocket engines. ****** [5M] [10M] [10M] [6M] [4M] [10M] [10M] [5M] [5M] [5M] [5M] Page 2 of 2 R15 Code No: R15A0313 MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) III B.Tech I Semester supplementary Examinations, May 2018 Advanced Thermal Engineering (ME) Roll No Time: 3 hours Max. Marks: 75 Note: This question paper contains two parts A and B Part A is compulsory which carriers 25 marks and Answer all questions. Part B Consists of 5 SECTIONS (One SECTION for each UNIT). Answer FIVE Questions, Choosing ONE Question from each SECTION and each Question carries 10 marks. Steam tables and Mollier chart may be permitted **** PART – A (25 Marks) 1. (a) How Rankine efficiency can be improved? (2M) (b) What are the advantages of Regenerative cycle? (3M) (c) What is the function of Fusible plug in steam boilers? (2M) (d) What do you understand by the term ‘Critical pressure’ as applied to steam nozzles? (3M) (e) Define Degree of reaction? (2M) (f) Give the difference between Impulse and Reaction Turbines? (3M) (g) What is meant by closed cycle gas turbine? (2M) (h) Why Re-heater is necessary in gas turbine? What are its effects? (3M) (i) What is Jet Propulsion? (2M) (j) Give the difference between ramjet and pulse jet engines? (3M) PART – B (50 Marks) SECTION – I 2. a) Show the Rankine cycle on p-v and T-s diagrams and explain the processes involved. Also draw the mechanical system to show different processes of the Rankine cycle. (5M) b) In an ideal reheat cycle, the steam enters the turbine at 30 bar and 500 0C.After expansion to 5 bar,the steam is reheated to 5000C and then expanded to the condenser pressure of 0.1 bar. Determine the cycle thermal efficiency, mass flow rate of steam. Take power output as 100MW. (5M) (OR) 3. a) What are the methods which can lead to increase in thermal efficiency of Rankine cycle? (5M) b) A steam power plant has boiler and condenser pressures of 60 bar and 0.1 bar, respectively. Steam coming out of the boiler is dry and saturated. The plant operates on the Rankine cycle. Calculate thermal efficiency. (5M) SECTION – II 4. a) With the help of neat sketch, explain Cochran Boiler. What are its special features? (5M) b) A nozzle is to be designed to expand steam at the rate of 0.10 kg/s from 500kPa, 2100C to 100kPa. Neglect inlet velocity of steam. For a nozzle efficiency of 0.9, determine the exit area of the nozzle. (5M) (OR) 5. a) What are the differentiating features between a water tube and fire tube boiler? (5M) b) Starting from the fundamentals, show that the maximum discharge through the nozzle,the ratio of throat pressure to inlet pressure is given by (2/n+1) n/n-1, where n is the index for isentropic expansion through the nozzle. (5M) SECTION – III 6. a) What is compounding? Describe various methods of compounding with neat sketches of arrangement, pressure and velocity profiles. (5M) b) The following data refers to a single stage impulse turbine: Steam velocity = 800m/s; Blade speed = 300 m/s; Nozzle angle = 200; Blade outlet angle = 250.Neglecting the effect of friction, calculate the power developed by the turbine for the steam flow rate of 25kg/s. Also calculate the axial thrust on the bearings. (5M) (OR) 7. a) Prove that for a 50% reaction turbines α=φ and θ=β. (5M) b) In one stage of a reaction turbine, both fixed and moving blades have inlet and outlet blade tip angles of 350 and 200 respectively. The mean blade speed is 80m/s and the steam consumption is 22500 kg/hr. Determine the power developed and stage efficiency if the isentropic heat drops in both fixed and moving rows is 23.5 kJ/kg in the pair. (5M) SECTION – IV 8. A gas turbine plant works between the temperature limits of 1152 K and 288 K. Isentropic efficiencies for Compressor and Turbine are 0.85 and 0.8 respectively. Determine the optimum pressure ratio for maximum work output and also find maximum cycle thermal efficiency. (10M) (OR) 9. Explain with neat sketch the gas turbine cycles with intercooling and reheating and what will be the condition of maximum output. (10M) SECTION – V 10. Why is thrust augmentation necessary? What are the methods for thrust augmentation in a turbojet engine? (10M) (OR) 11. What are composite and homogeneous solid propellants? How do they work? State their merits and demerits. (10M) *******