To see whether the turbulent flow correlations derived for circular ducts can be used for hexagon... more To see whether the turbulent flow correlations derived for circular ducts can be used for hexagonal cross-sectional ducts using hydraulic diameter, turbulent flow in hexagonal ducts is numerically investigated under constant wall temperature boundary condition using ANSYS Fluent 17.0 software. Investigated parameters are the Reynolds number between 10×103Re50×103 and side angle of the duct varying between 30o and 90o. Standard k-ε model is used as turbulence model. General expressions are proposed for fully developed dimensionless heat transfer coefficient Nusselt number and fully developed Darcy friction factor in terms of Reynolds number and side angle for hexagonal-shaped cross-sectional duct. Results show that side angle of hexagonal duct affects the pressure drop along duct and heat transfer coefficient in duct. Results point out that regular hexagonal duct, =60o, gives minimum pressure drop and maximum Nusselt number. It is concluded that correlations given in the literatur...
The 2-D periodically fully developed laminar forced convection fluid flow and heat transfer chara... more The 2-D periodically fully developed laminar forced convection fluid flow and heat transfer characteristics in a horizontal channel with staggered fins are investigated numerically under constant wall heat flux boundary condition. Study is performed using ANSYS Fluent 6.3.26 which uses finite volume method. Air (Pr @ 0.7) and Freon-12 (Pr @ 3.5) are used as working fluids. Effects of Reynolds number, Prandtl number, fin height, and distances between two fins on heat transfer and friction factor are examined. Results are given in the form of non-dimensional average Nusselt number and average Darcy friction factor as a function of Reynolds number for different fin distances and Prandtl numbers. The velocity and temperature profiles are also obtained. It is seen that as the fin distance increases, behavior approaches the finless channel, as expected. Also, thermal enhancement factors are given graphically for working fluids. It is seen that heat transfer dominates the friction as both ...
Özet: Yamuk kesitli kanal içerisindeki laminer zorlanmış konveksiyon ısıl cihazların tasarım ilgi... more Özet: Yamuk kesitli kanal içerisindeki laminer zorlanmış konveksiyon ısıl cihazların tasarım ilgi alanları içerisindedir. Yamuk kesit alanına sahip bir kanal içerisindeki hidrodinamik ve ısıl olarak gelişmekte olan üç boyutlu zorlanmış konveksiyon ısı transferi kararlı rejim ve sabit yüzey sıcaklığı şartlarında sayısal olarak incelenmiştir. Sayısal çalışma Reynolds sayısının 100≤Re≤800 aralığında gerçekleştirilmiştir. Çalışma akışkanı olarak hava (Pr≅0.7) kullanılmıştır. Sayısal çalışma ticari Sayısal Akışkanlar Dinamiği yazılımı olan Ansys Fluent 6.3.26 ile gerçekleştirilmiştir. Ortalama Nusselt sayıları ve sürtünme katsayıları Reynolds sayısının fonksiyonu olarak sunulmuştur. Yerel Nusselt sayıları ve Fanning sürtünme faktörleri kanal boyunca mesafenin fonksiyonu olarak çizilmiştir. Hız ve sıcaklık dağılımları kanal boyunca farklı pozisyonlarda sunulmuştur.
n-heptane pool fire was numerically and experimentally investigated in a 1:100 scaled metro stati... more n-heptane pool fire was numerically and experimentally investigated in a 1:100 scaled metro station. Fire Dynamics Simulator (FDS v6.7.5) has been applied to investigate smoke and temperature distribution by implementing different design curves in the station. Experimental and numerical studies were performed for 10 ml n-heptane fuel under zero piston effect. To develop performance-based design and to obtain reliable fire simulation results for structures, reasonable input conditions are essential for numerical studies. The aim of the study is to select most suitable fire design curve and make the numerical study independent of the experimental results for small scale hydrocarbon pool fires. In this study, t 2 , tanh, Eurocode 1 (BS EN 1991-1-2), exponential, and quadratic fire curves were investigated and validated with experimental results. The numerical results obtained using FDS were validated with experimental data and good agreement was observed for all design fire curves except quadratic one. It was observed that the exponential design fire curve predicted more similarly to the experimental data over the fire duration including growth, fully developed and decay phases. Regardless of the experimental results, it was seen that the temperature distribution results obtained from the numerical study using exponential fire design curve and the radiation / turbulence parameters obtained from the literature were found to have an average of 5% difference with the experimental results. It was also seen that the t 2 and tanh curves have acceptable differences of 6.92% and 9.02%, respectively, and the Eurocode HC is less suitable than the other curves with a difference of 12.17%. Therefore, it can be said that in small scale hydrocarbon pool fires, fire design can be done using exponential design curve.
The flow and heat transfer characteristics of the TiO2-water nanofluid assuming as a single-phase... more The flow and heat transfer characteristics of the TiO2-water nanofluid assuming as a single-phase in the rectangular offset strip fin structure for different Reynolds number (500-1000) and TiO2 nanoparticle volume concentration values (0-4%) were investigated numerically under 3-D, steady-state, and laminar flow conditions. Simulations were also performed for 1% and 4% nanoparticle volume concentrations of Al2O3-water nanofluid, and the results were compared with those of TiO2-water nanofluid. Results show that when the TiO2-water nanofluid is used, the heat transfer rate, heat transfer coefficient, and Nusselt number increase with increasing both Reynolds number and nanoparticle volume concentration, and parallel to these, both pressure loss, and pumping power increase. Considering the values of the performance evaluation criteria number, it is clear that the use of TiO2-water nanofluid in offset strip fin structure at all Reynolds numbers examined between 1-4% volume concentration...
Gas cyclone separators are employed to separate particles from gas. In this study, the effect of ... more Gas cyclone separators are employed to separate particles from gas. In this study, the effect of the vortex finder diameter, inlet velocity and particle size on the flow field and the performance of a large industrial Stairmand cyclone has been studied both experimentally and numerically. The vortex finder diameters used are 0.40, 0.45, 0.50 and 0.55 times the cyclone diameter. Cyclones with body diameters of 700 mm and 254 mm are used. Cyclone inlet velocity is changed from 11.5 m•s −1 to 19 m•s −1. Particle size is varied between 1 and 13 μm. Whether the correlations obtained for small-scale cyclones are valid for large-scale cyclones has been investigated. The three-dimensional numerical study is carried out by using ANSYS Fluent 17.0 software package for incompressible turbulent flow condition. Reynolds stress model is chosen as the turbulence model. Sawdust ash is used as particles. The results of numerical study are compared with the results of experimental study and literature. Results are found to be consistent with each other. It is seen that cyclone collection efficiency and pressure drop increase when both vortex finder diameter decreases and inlet velocity increases, but 50% cutoff diameter decreases. Results show that the correlations obtained for small sampling cyclones may not be appropriate for large-scale cyclones. Keywords Cyclone separators. Reynolds stress model. CFD. Experimental study. Vortex finder Nomenclature a cyclone inlet height, m. b cyclone inlet width, m. B cone-tipdiameter ,m. c length of inlet section, m. C D the drag coefficient, −. D cyclone body diameter, m. D c core diameter of cyclone, m. D e vortex finder diameter, m. D h hydraulic diameter, m. D p particle diameter, m. D 50 particle cutoff diameter, m. g i gravitational acceleration in i-direction, m•s −2. h height of cyclone cylinder part, m. h e vortex finder length outside the cyclone, m. ΔH dimensionless parameter, −.
Iranian Journal of Science and Technology, Transactions of Mechanical Engineering, 2016
Three-dimensional turbulent-forced convection flow, heat transfer and second-law analysis in a ci... more Three-dimensional turbulent-forced convection flow, heat transfer and second-law analysis in a circular duct having single baffle have been examined numerically under uniform constant wall heat flux boundary condition at steady state. Baffle is attached in the entrance, middle and exit regions of the test section. ANSYS Fluent 15 which uses finite-volume method has been employed for numerical analysis. The effects of Reynolds number Re changing from 3000 to 50,000 and dimensionless position of baffle S/D = 1, 16.1 and 25 are investigated for Prandtl number of Pr = 0.7 and baffle angle of a = 90°. It is seen that circular duct with single baffle has a higher Nusselt number, friction factor and entropy generation rate compared to the circular duct without baffle. It is also seen that the duct with baffle in the inlet region has a higher value of Nusselt number and friction factor. The duct having baffle in the middle region has a maximum thermal performance and low entropy generation rate. The accuracy of the results is validated by comparing the obtained results with the results of smooth duct. Keywords Friction Á Heat transfer Á Entropy generation Á Heat flux Á Turbulent flow Á Baffle List of Symbols A c Cross-sectional area (m 2) c p Specific heat at constant pressure (J kg-1 K-1) C l Constant (-) D Diameter of the circular duct (m) f Averaged Darcy friction factor (-) G k Production rate (kg m-1 s-3) & O.
Microwave cancer therapy is an effective method used to destroy cancer cells which eliminates the... more Microwave cancer therapy is an effective method used to destroy cancer cells which eliminates the need for surgical intervention in diseases such as breast and liver cancer. The present study aims to present a methodology for the destruction of killing the malignant cells in a wider periphery by means of burning in a shorter time meanwhile causing minimal damage to the healthy tissues. The study is carried out for a frequency value of 2.45 GHz and for a power value of 10 W using finite element methods. A comparison between coaxial single-slot antenna and double-slot antenna is conducted for liver and breast tissues. Investigated parameters are the slot number, the type of the tissue and the duration of microwave cancer therapy. The specific absorption rate and temperature distribution are the examined parameters. The results of the study show that both peak specific absorption rate and peak temperature value are obtained for microwave coaxial single slot antenna within the liver tissue, and it is observed that the temperature distribution depends on time. Maximum temperature value is attained as 93.9 o C and 82.8 o C for single and double slot antennas for liver tissue whereas the so-called values are 93.0 o C and 69.8 o C for breast tissue. New correlations are given for the treatment of liver and breast tissues using coaxial single slot antenna. It is anticipated that the present study makes a contribution in the field of medicine.
In this study, an air window collector having vertical black blinds was investigated experimental... more In this study, an air window collector having vertical black blinds was investigated experimentally under actual outdoor conditions. The vertical blind was installed between two 120 x 80 cm glass panes. It can rotate about the vertical axis. The fully open position makes a 90 ° angle with the vertical plane. A commercially available blind made of cloth and coated with black paint was tested. The air circulation in the system is provided by a fan parallel to blinds. Various parameters were measured and recorded using a data acquisition system. The effect of these parameters on the thermal performance of the system were determined experimentally.
Two-dimensional periodically fully developed laminar forced convection fluid flow and heat transf... more Two-dimensional periodically fully developed laminar forced convection fluid flow and heat transfer characteristics in a horizontal channel with staggered fins are investigated numerically under constant wall heat flux boundary condition. Study is performed using ANSYS Fluent 6.3.26 which uses finite volume method. Air (Pr 0.7) and Freon-12 (Pr 3.5) are used as working fluids. Effects of Reynolds number, Prandtl number, fin height, and distances between two fins on heat transfer and friction factor are examined. Results are given in the form of non-dimensional average Nusselt number and average Darcy friction factor as a function of Reynolds number for different fin distances and Prandtl numbers. The velocity and temperature profiles are also obtained. It is seen that as the fin distance increases, behavior approaches the finless channel, as expected. Also, thermal enhancement factors are given graphically for working fluids. It is seen that heat transfer dominates the friction as b...
Bu calismanin amaci radyofrekans ablasyon metodunu kullanarak kuresel sekilli karaciger tumorleri... more Bu calismanin amaci radyofrekans ablasyon metodunu kullanarak kuresel sekilli karaciger tumorlerinin yok edilmesidir. Uc boyutlu sonlu elemanlar metodu kullanilmistir. Karaciger dokusu icin bes farkli radyofrekans prop kuresel sekilli lezyonu olusturmak icin kullanilmistir. Incelenen parametreler elektrik voltaji, ablasyon suresi, geometri ve elektrot sayisidir. Sonuclar lezyon hacmi ve sicaklik dagilimi olarak verilmistir. Sonuclar literatur sonuclari ile kiyaslanmis ve sonuclarin literatur sonuclari ile uyum icinde oldugu gorulmustur. Sonuclar bir kuresel sekilli karaciger tumorunun dort elektrotlu yilbasi agaci tipi ve dort elektrotlu semsiye-tipi elektrotlardan olusan hibrit bir elektrot konstruksiyonuyla yok edilebilecegini gostermistir. Yaklasik 20 mm capindaki bir lezyonun sekiz dakika sonunda hibrit elektrot dizayni ile yok edilebildigi gorulmustur. Hibrit elektrot konfigurasyonunun klinik uygulamalarda kuresel sekilli karaciger tumorlerinin tedavisi icin kullanilmasi umulma...
In this study, steady-state 3-D turbulent forced convection flow and heat transfer characteristic... more In this study, steady-state 3-D turbulent forced convection flow and heat transfer characteristics in a circular pipe with baffles attached inside pipe have been numerically investigated under constant wall heat flux boundary condition. Numerical study has been carried out for Reynolds number of 3000-50,000, Prandtl number of 0.71, baffle distances s/D of 1, 2, and 3, and baffle angle α of 30°-150°. Ansys Fluent 12.0.1 software has been used to solve the flow field. It is observed that circular pipe having baffles has a higher Nusselt number and friction factor compared to the smooth circular pipe without baffles. Periodically fully developed conditions are obtained after a certain module. Maximum thermal performance factor is obtained for the baffle angle of 150°. Results show that baffle distance, baffle angle, and Reynolds number play important role on both flow and heat transfer characteristics. All the numerical results are correlated within accuracy of ±10% and ±15% for averag...
Nanorefrigerants are produced by dispersion of nanometer sized (1-100 nm) solid particles having ... more Nanorefrigerants are produced by dispersion of nanometer sized (1-100 nm) solid particles having high thermal conductivity such as Cu, Al2O3, ZnO, CuO, etc. in a refrigerant and used in engineering devices to enhance the heat transfer capabilities. They are used in numerous applications such as tribology, chemistry, environmental areas, surfactants and coating, pharmaceutical and medical applications, microprocessors, jacket water cooling in vehicles and fuel cells. In this study, forced convection fluid flow and heat transfer characteristics of R600a/Al2O3 nanorefrigerant have been investigated numerically. Three different nanoparticle volume fractions (0.8, 2.0 and 4.0%) were used in numerical calculations. Numerical study has been implemented under three-dimensional steady-state laminar flow condition. The circular cross-sectioned duct geometry with uniform surface heat flux has been used as computational domain. The effect of nanorefrigerant and nanoparticle volume fraction on t...
Bu calismada, yatay siyah jaluzili hava tutuculu bir kollektorun isil performansi kisin gercek ce... more Bu calismada, yatay siyah jaluzili hava tutuculu bir kollektorun isil performansi kisin gercek cevre sartlarinda deneysel olarak incelenmistir. Jaluzi 1.20 x 0.80 m’lik iki pencere cami arasina yerlestirilmis olup yatay eksen etrafinda donmektedir ve tam acik pozisyonda yataydir. Piyasada satilmakta olan aluminyumdan yapilmis ve siyaha boyanmis jaluzi, enerji absorbe edici yuzey olarak kullanilmistir. Sistem icerisindeki hava sirkulasyonu bir fan ile saglanmistir. Bir data toplama cihazi kullanilarak cevre sicakligi, test odasinin ic sicakligi, kollektor giris ve cikis sicakliklari, ic camin ic yuzey sicakligi, zemin, tavan, test odasinin kuzey, bati ve dogu taraflarindaki duvarlarin yuzey sicakliklari ve kollektor yuzeyine gelen radyasyon miktari olculmus ve kaydedilmistir. Kutlesel debi, pencereler arasindaki mesafe, dilimlerin egim acisinin hava-tutuculu pencerenin isil performansi uzerindeki etkisi deneysel olarak arastirilmis ve sekillerle gosterilmistir. Kutlesel debide meydan...
Abstract– Three-dimensional laminar flow and heat transfer characteristics in smooth hexagonal du... more Abstract– Three-dimensional laminar flow and heat transfer characteristics in smooth hexagonal ducts with equal sides have been numerically investigated in the Reynolds number range from 300 to 2000. The numerical solutions are obtained for both axially and peripherally constant wall temperature (T) and heat flux (H2) thermal boundary conditions for five different values of the duct angle ( = 30, 45, 60, 75, and 90). Local Fanning friction factor and Nusselt number are obtained along the duct. Hydrodynamic and thermal entrance lengths have been determined. The accuracy of the results obtained in this study is verified by comparing the results with those available in the literature. Results show that duct geometry plays an important role on both flow and heat transfer characteristics. It is seen that the thermal entrance length for H2 boundary condition is greater than that for T boundary condition. Minimum hydrodynamic and thermal entrance lengths are obtained for = 60, regular d...
Süleyman Demirel Üniversitesi Fen Bilimleri Enstitüsü Dergisi, 2014
In this study, hydrodynamically and thermally developing laminar flow and heat transfer in a rect... more In this study, hydrodynamically and thermally developing laminar flow and heat transfer in a rectangular cross-sectional duct have been numerically investigated for steady state and constant surface temperature boundary condition. Numerical solutions have been made for three different aspect ratios (α=0.25, 0.50 and 1.0) and in the Reynolds numbers range of 600 to 2000. Air (Pr0.72) is used as working fluid. A commercial CFD program ANSYS Fluent 13.0 has been employed to carry out the numerical study. Results are given in terms of Nusselt number Nu, Darcy friction factor f, hydrodynamic Lhd and thermal entrance Lth lengths as a function of Reynolds number Re. Also, velocity and temperature contours in the duct are given for different Reynolds numbers. It is seen that the general equation given for circular ducts does not give a true hydrodynamic and thermal entrance length for rectangular ducts. The present results obtained from numerical study are correlated as a function of aspec...
Çankaya University Journal of Humanities and Social Sciences, 2012
In this study, steady-state hydrodynamically fully developed thermally developing three-dimension... more In this study, steady-state hydrodynamically fully developed thermally developing three-dimensional laminar forced convection flow and heat transfer in a horizontal smooth trapezoidal duct were numerically investigated under uniform surface temperature condition. Numerical study was carried out for a Reynolds number range of 100 to 1000. Air (P r ∼= 0.7) was used as the heat transfer medium. A commercial CFD program Fluent 12.1 was used to carry out the numerical study. Average Nusselt numbers and average Darcy friction factors were presented for different Reynolds numbers. Local Nusselt numbers were plotted as a function of the distance along the duct. Velocity and temperature contours were given as graphically at different positions along the duct. The results obtained from this study were compared with the results of similar studies available in the literature, and the results were found to be in good agreement. It is seen that increase in Reynolds number causes decrease in frict...
To see whether the turbulent flow correlations derived for circular ducts can be used for hexagon... more To see whether the turbulent flow correlations derived for circular ducts can be used for hexagonal cross-sectional ducts using hydraulic diameter, turbulent flow in hexagonal ducts is numerically investigated under constant wall temperature boundary condition using ANSYS Fluent 17.0 software. Investigated parameters are the Reynolds number between 10×103Re50×103 and side angle of the duct varying between 30o and 90o. Standard k-ε model is used as turbulence model. General expressions are proposed for fully developed dimensionless heat transfer coefficient Nusselt number and fully developed Darcy friction factor in terms of Reynolds number and side angle for hexagonal-shaped cross-sectional duct. Results show that side angle of hexagonal duct affects the pressure drop along duct and heat transfer coefficient in duct. Results point out that regular hexagonal duct, =60o, gives minimum pressure drop and maximum Nusselt number. It is concluded that correlations given in the literatur...
The 2-D periodically fully developed laminar forced convection fluid flow and heat transfer chara... more The 2-D periodically fully developed laminar forced convection fluid flow and heat transfer characteristics in a horizontal channel with staggered fins are investigated numerically under constant wall heat flux boundary condition. Study is performed using ANSYS Fluent 6.3.26 which uses finite volume method. Air (Pr @ 0.7) and Freon-12 (Pr @ 3.5) are used as working fluids. Effects of Reynolds number, Prandtl number, fin height, and distances between two fins on heat transfer and friction factor are examined. Results are given in the form of non-dimensional average Nusselt number and average Darcy friction factor as a function of Reynolds number for different fin distances and Prandtl numbers. The velocity and temperature profiles are also obtained. It is seen that as the fin distance increases, behavior approaches the finless channel, as expected. Also, thermal enhancement factors are given graphically for working fluids. It is seen that heat transfer dominates the friction as both ...
Özet: Yamuk kesitli kanal içerisindeki laminer zorlanmış konveksiyon ısıl cihazların tasarım ilgi... more Özet: Yamuk kesitli kanal içerisindeki laminer zorlanmış konveksiyon ısıl cihazların tasarım ilgi alanları içerisindedir. Yamuk kesit alanına sahip bir kanal içerisindeki hidrodinamik ve ısıl olarak gelişmekte olan üç boyutlu zorlanmış konveksiyon ısı transferi kararlı rejim ve sabit yüzey sıcaklığı şartlarında sayısal olarak incelenmiştir. Sayısal çalışma Reynolds sayısının 100≤Re≤800 aralığında gerçekleştirilmiştir. Çalışma akışkanı olarak hava (Pr≅0.7) kullanılmıştır. Sayısal çalışma ticari Sayısal Akışkanlar Dinamiği yazılımı olan Ansys Fluent 6.3.26 ile gerçekleştirilmiştir. Ortalama Nusselt sayıları ve sürtünme katsayıları Reynolds sayısının fonksiyonu olarak sunulmuştur. Yerel Nusselt sayıları ve Fanning sürtünme faktörleri kanal boyunca mesafenin fonksiyonu olarak çizilmiştir. Hız ve sıcaklık dağılımları kanal boyunca farklı pozisyonlarda sunulmuştur.
n-heptane pool fire was numerically and experimentally investigated in a 1:100 scaled metro stati... more n-heptane pool fire was numerically and experimentally investigated in a 1:100 scaled metro station. Fire Dynamics Simulator (FDS v6.7.5) has been applied to investigate smoke and temperature distribution by implementing different design curves in the station. Experimental and numerical studies were performed for 10 ml n-heptane fuel under zero piston effect. To develop performance-based design and to obtain reliable fire simulation results for structures, reasonable input conditions are essential for numerical studies. The aim of the study is to select most suitable fire design curve and make the numerical study independent of the experimental results for small scale hydrocarbon pool fires. In this study, t 2 , tanh, Eurocode 1 (BS EN 1991-1-2), exponential, and quadratic fire curves were investigated and validated with experimental results. The numerical results obtained using FDS were validated with experimental data and good agreement was observed for all design fire curves except quadratic one. It was observed that the exponential design fire curve predicted more similarly to the experimental data over the fire duration including growth, fully developed and decay phases. Regardless of the experimental results, it was seen that the temperature distribution results obtained from the numerical study using exponential fire design curve and the radiation / turbulence parameters obtained from the literature were found to have an average of 5% difference with the experimental results. It was also seen that the t 2 and tanh curves have acceptable differences of 6.92% and 9.02%, respectively, and the Eurocode HC is less suitable than the other curves with a difference of 12.17%. Therefore, it can be said that in small scale hydrocarbon pool fires, fire design can be done using exponential design curve.
The flow and heat transfer characteristics of the TiO2-water nanofluid assuming as a single-phase... more The flow and heat transfer characteristics of the TiO2-water nanofluid assuming as a single-phase in the rectangular offset strip fin structure for different Reynolds number (500-1000) and TiO2 nanoparticle volume concentration values (0-4%) were investigated numerically under 3-D, steady-state, and laminar flow conditions. Simulations were also performed for 1% and 4% nanoparticle volume concentrations of Al2O3-water nanofluid, and the results were compared with those of TiO2-water nanofluid. Results show that when the TiO2-water nanofluid is used, the heat transfer rate, heat transfer coefficient, and Nusselt number increase with increasing both Reynolds number and nanoparticle volume concentration, and parallel to these, both pressure loss, and pumping power increase. Considering the values of the performance evaluation criteria number, it is clear that the use of TiO2-water nanofluid in offset strip fin structure at all Reynolds numbers examined between 1-4% volume concentration...
Gas cyclone separators are employed to separate particles from gas. In this study, the effect of ... more Gas cyclone separators are employed to separate particles from gas. In this study, the effect of the vortex finder diameter, inlet velocity and particle size on the flow field and the performance of a large industrial Stairmand cyclone has been studied both experimentally and numerically. The vortex finder diameters used are 0.40, 0.45, 0.50 and 0.55 times the cyclone diameter. Cyclones with body diameters of 700 mm and 254 mm are used. Cyclone inlet velocity is changed from 11.5 m•s −1 to 19 m•s −1. Particle size is varied between 1 and 13 μm. Whether the correlations obtained for small-scale cyclones are valid for large-scale cyclones has been investigated. The three-dimensional numerical study is carried out by using ANSYS Fluent 17.0 software package for incompressible turbulent flow condition. Reynolds stress model is chosen as the turbulence model. Sawdust ash is used as particles. The results of numerical study are compared with the results of experimental study and literature. Results are found to be consistent with each other. It is seen that cyclone collection efficiency and pressure drop increase when both vortex finder diameter decreases and inlet velocity increases, but 50% cutoff diameter decreases. Results show that the correlations obtained for small sampling cyclones may not be appropriate for large-scale cyclones. Keywords Cyclone separators. Reynolds stress model. CFD. Experimental study. Vortex finder Nomenclature a cyclone inlet height, m. b cyclone inlet width, m. B cone-tipdiameter ,m. c length of inlet section, m. C D the drag coefficient, −. D cyclone body diameter, m. D c core diameter of cyclone, m. D e vortex finder diameter, m. D h hydraulic diameter, m. D p particle diameter, m. D 50 particle cutoff diameter, m. g i gravitational acceleration in i-direction, m•s −2. h height of cyclone cylinder part, m. h e vortex finder length outside the cyclone, m. ΔH dimensionless parameter, −.
Iranian Journal of Science and Technology, Transactions of Mechanical Engineering, 2016
Three-dimensional turbulent-forced convection flow, heat transfer and second-law analysis in a ci... more Three-dimensional turbulent-forced convection flow, heat transfer and second-law analysis in a circular duct having single baffle have been examined numerically under uniform constant wall heat flux boundary condition at steady state. Baffle is attached in the entrance, middle and exit regions of the test section. ANSYS Fluent 15 which uses finite-volume method has been employed for numerical analysis. The effects of Reynolds number Re changing from 3000 to 50,000 and dimensionless position of baffle S/D = 1, 16.1 and 25 are investigated for Prandtl number of Pr = 0.7 and baffle angle of a = 90°. It is seen that circular duct with single baffle has a higher Nusselt number, friction factor and entropy generation rate compared to the circular duct without baffle. It is also seen that the duct with baffle in the inlet region has a higher value of Nusselt number and friction factor. The duct having baffle in the middle region has a maximum thermal performance and low entropy generation rate. The accuracy of the results is validated by comparing the obtained results with the results of smooth duct. Keywords Friction Á Heat transfer Á Entropy generation Á Heat flux Á Turbulent flow Á Baffle List of Symbols A c Cross-sectional area (m 2) c p Specific heat at constant pressure (J kg-1 K-1) C l Constant (-) D Diameter of the circular duct (m) f Averaged Darcy friction factor (-) G k Production rate (kg m-1 s-3) & O.
Microwave cancer therapy is an effective method used to destroy cancer cells which eliminates the... more Microwave cancer therapy is an effective method used to destroy cancer cells which eliminates the need for surgical intervention in diseases such as breast and liver cancer. The present study aims to present a methodology for the destruction of killing the malignant cells in a wider periphery by means of burning in a shorter time meanwhile causing minimal damage to the healthy tissues. The study is carried out for a frequency value of 2.45 GHz and for a power value of 10 W using finite element methods. A comparison between coaxial single-slot antenna and double-slot antenna is conducted for liver and breast tissues. Investigated parameters are the slot number, the type of the tissue and the duration of microwave cancer therapy. The specific absorption rate and temperature distribution are the examined parameters. The results of the study show that both peak specific absorption rate and peak temperature value are obtained for microwave coaxial single slot antenna within the liver tissue, and it is observed that the temperature distribution depends on time. Maximum temperature value is attained as 93.9 o C and 82.8 o C for single and double slot antennas for liver tissue whereas the so-called values are 93.0 o C and 69.8 o C for breast tissue. New correlations are given for the treatment of liver and breast tissues using coaxial single slot antenna. It is anticipated that the present study makes a contribution in the field of medicine.
In this study, an air window collector having vertical black blinds was investigated experimental... more In this study, an air window collector having vertical black blinds was investigated experimentally under actual outdoor conditions. The vertical blind was installed between two 120 x 80 cm glass panes. It can rotate about the vertical axis. The fully open position makes a 90 ° angle with the vertical plane. A commercially available blind made of cloth and coated with black paint was tested. The air circulation in the system is provided by a fan parallel to blinds. Various parameters were measured and recorded using a data acquisition system. The effect of these parameters on the thermal performance of the system were determined experimentally.
Two-dimensional periodically fully developed laminar forced convection fluid flow and heat transf... more Two-dimensional periodically fully developed laminar forced convection fluid flow and heat transfer characteristics in a horizontal channel with staggered fins are investigated numerically under constant wall heat flux boundary condition. Study is performed using ANSYS Fluent 6.3.26 which uses finite volume method. Air (Pr 0.7) and Freon-12 (Pr 3.5) are used as working fluids. Effects of Reynolds number, Prandtl number, fin height, and distances between two fins on heat transfer and friction factor are examined. Results are given in the form of non-dimensional average Nusselt number and average Darcy friction factor as a function of Reynolds number for different fin distances and Prandtl numbers. The velocity and temperature profiles are also obtained. It is seen that as the fin distance increases, behavior approaches the finless channel, as expected. Also, thermal enhancement factors are given graphically for working fluids. It is seen that heat transfer dominates the friction as b...
Bu calismanin amaci radyofrekans ablasyon metodunu kullanarak kuresel sekilli karaciger tumorleri... more Bu calismanin amaci radyofrekans ablasyon metodunu kullanarak kuresel sekilli karaciger tumorlerinin yok edilmesidir. Uc boyutlu sonlu elemanlar metodu kullanilmistir. Karaciger dokusu icin bes farkli radyofrekans prop kuresel sekilli lezyonu olusturmak icin kullanilmistir. Incelenen parametreler elektrik voltaji, ablasyon suresi, geometri ve elektrot sayisidir. Sonuclar lezyon hacmi ve sicaklik dagilimi olarak verilmistir. Sonuclar literatur sonuclari ile kiyaslanmis ve sonuclarin literatur sonuclari ile uyum icinde oldugu gorulmustur. Sonuclar bir kuresel sekilli karaciger tumorunun dort elektrotlu yilbasi agaci tipi ve dort elektrotlu semsiye-tipi elektrotlardan olusan hibrit bir elektrot konstruksiyonuyla yok edilebilecegini gostermistir. Yaklasik 20 mm capindaki bir lezyonun sekiz dakika sonunda hibrit elektrot dizayni ile yok edilebildigi gorulmustur. Hibrit elektrot konfigurasyonunun klinik uygulamalarda kuresel sekilli karaciger tumorlerinin tedavisi icin kullanilmasi umulma...
In this study, steady-state 3-D turbulent forced convection flow and heat transfer characteristic... more In this study, steady-state 3-D turbulent forced convection flow and heat transfer characteristics in a circular pipe with baffles attached inside pipe have been numerically investigated under constant wall heat flux boundary condition. Numerical study has been carried out for Reynolds number of 3000-50,000, Prandtl number of 0.71, baffle distances s/D of 1, 2, and 3, and baffle angle α of 30°-150°. Ansys Fluent 12.0.1 software has been used to solve the flow field. It is observed that circular pipe having baffles has a higher Nusselt number and friction factor compared to the smooth circular pipe without baffles. Periodically fully developed conditions are obtained after a certain module. Maximum thermal performance factor is obtained for the baffle angle of 150°. Results show that baffle distance, baffle angle, and Reynolds number play important role on both flow and heat transfer characteristics. All the numerical results are correlated within accuracy of ±10% and ±15% for averag...
Nanorefrigerants are produced by dispersion of nanometer sized (1-100 nm) solid particles having ... more Nanorefrigerants are produced by dispersion of nanometer sized (1-100 nm) solid particles having high thermal conductivity such as Cu, Al2O3, ZnO, CuO, etc. in a refrigerant and used in engineering devices to enhance the heat transfer capabilities. They are used in numerous applications such as tribology, chemistry, environmental areas, surfactants and coating, pharmaceutical and medical applications, microprocessors, jacket water cooling in vehicles and fuel cells. In this study, forced convection fluid flow and heat transfer characteristics of R600a/Al2O3 nanorefrigerant have been investigated numerically. Three different nanoparticle volume fractions (0.8, 2.0 and 4.0%) were used in numerical calculations. Numerical study has been implemented under three-dimensional steady-state laminar flow condition. The circular cross-sectioned duct geometry with uniform surface heat flux has been used as computational domain. The effect of nanorefrigerant and nanoparticle volume fraction on t...
Bu calismada, yatay siyah jaluzili hava tutuculu bir kollektorun isil performansi kisin gercek ce... more Bu calismada, yatay siyah jaluzili hava tutuculu bir kollektorun isil performansi kisin gercek cevre sartlarinda deneysel olarak incelenmistir. Jaluzi 1.20 x 0.80 m’lik iki pencere cami arasina yerlestirilmis olup yatay eksen etrafinda donmektedir ve tam acik pozisyonda yataydir. Piyasada satilmakta olan aluminyumdan yapilmis ve siyaha boyanmis jaluzi, enerji absorbe edici yuzey olarak kullanilmistir. Sistem icerisindeki hava sirkulasyonu bir fan ile saglanmistir. Bir data toplama cihazi kullanilarak cevre sicakligi, test odasinin ic sicakligi, kollektor giris ve cikis sicakliklari, ic camin ic yuzey sicakligi, zemin, tavan, test odasinin kuzey, bati ve dogu taraflarindaki duvarlarin yuzey sicakliklari ve kollektor yuzeyine gelen radyasyon miktari olculmus ve kaydedilmistir. Kutlesel debi, pencereler arasindaki mesafe, dilimlerin egim acisinin hava-tutuculu pencerenin isil performansi uzerindeki etkisi deneysel olarak arastirilmis ve sekillerle gosterilmistir. Kutlesel debide meydan...
Abstract– Three-dimensional laminar flow and heat transfer characteristics in smooth hexagonal du... more Abstract– Three-dimensional laminar flow and heat transfer characteristics in smooth hexagonal ducts with equal sides have been numerically investigated in the Reynolds number range from 300 to 2000. The numerical solutions are obtained for both axially and peripherally constant wall temperature (T) and heat flux (H2) thermal boundary conditions for five different values of the duct angle ( = 30, 45, 60, 75, and 90). Local Fanning friction factor and Nusselt number are obtained along the duct. Hydrodynamic and thermal entrance lengths have been determined. The accuracy of the results obtained in this study is verified by comparing the results with those available in the literature. Results show that duct geometry plays an important role on both flow and heat transfer characteristics. It is seen that the thermal entrance length for H2 boundary condition is greater than that for T boundary condition. Minimum hydrodynamic and thermal entrance lengths are obtained for = 60, regular d...
Süleyman Demirel Üniversitesi Fen Bilimleri Enstitüsü Dergisi, 2014
In this study, hydrodynamically and thermally developing laminar flow and heat transfer in a rect... more In this study, hydrodynamically and thermally developing laminar flow and heat transfer in a rectangular cross-sectional duct have been numerically investigated for steady state and constant surface temperature boundary condition. Numerical solutions have been made for three different aspect ratios (α=0.25, 0.50 and 1.0) and in the Reynolds numbers range of 600 to 2000. Air (Pr0.72) is used as working fluid. A commercial CFD program ANSYS Fluent 13.0 has been employed to carry out the numerical study. Results are given in terms of Nusselt number Nu, Darcy friction factor f, hydrodynamic Lhd and thermal entrance Lth lengths as a function of Reynolds number Re. Also, velocity and temperature contours in the duct are given for different Reynolds numbers. It is seen that the general equation given for circular ducts does not give a true hydrodynamic and thermal entrance length for rectangular ducts. The present results obtained from numerical study are correlated as a function of aspec...
Çankaya University Journal of Humanities and Social Sciences, 2012
In this study, steady-state hydrodynamically fully developed thermally developing three-dimension... more In this study, steady-state hydrodynamically fully developed thermally developing three-dimensional laminar forced convection flow and heat transfer in a horizontal smooth trapezoidal duct were numerically investigated under uniform surface temperature condition. Numerical study was carried out for a Reynolds number range of 100 to 1000. Air (P r ∼= 0.7) was used as the heat transfer medium. A commercial CFD program Fluent 12.1 was used to carry out the numerical study. Average Nusselt numbers and average Darcy friction factors were presented for different Reynolds numbers. Local Nusselt numbers were plotted as a function of the distance along the duct. Velocity and temperature contours were given as graphically at different positions along the duct. The results obtained from this study were compared with the results of similar studies available in the literature, and the results were found to be in good agreement. It is seen that increase in Reynolds number causes decrease in frict...
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Papers by OĞUZ TURGUT