Papers by saeed moghaddam
Journal of Thermal Science and Engineering Applications, 2020
is one of the well-known names in the field of flow boiling. He was born in June 1950 in India. H... more is one of the well-known names in the field of flow boiling. He was born in June 1950 in India. He received his B.S. in Mechanical Engineering from Marathawada University, India. He received his M.S. and Ph.D. degrees from the Department of Mechanical Engineering at the Indian Institute of Technology (IIT) in Mumbai, India. His supervisor was Prof. S. P. Sukhatme. After finishing his Ph.D. in 1975, Prof. Kandlikar became a faculty member in the Department of Mechanical Engineering at IIT before coming to Rochester Institute of Technology (RIT), in Rochester, New York, in 1980. Currently, he is the Gleason Professor of Mechanical Engineering in the Department of Mechanical Engineering, Rochester Institute of Technology. He was the founder of the RIT Thermal Analysis and Microfluidics Laboratory in 1990, which examines essential phenomena related to microscale fluid dynamics and mechanics. During his career at RIT, Prof. Kandlikar became involved in several activities. For instance, he founded the ASME Heat Transfer chapter in Rochester. He also founded and served as the first Chairman of the E-cubed fair-science and engineering fair for middle school students in celebration of Engineers Week.
Water heating and dehumidification are major energy consumers in buildings. The novel semi-open a... more Water heating and dehumidification are major energy consumers in buildings. The novel semi-open absorption heat pump design utilizes the heat of absorption from the dehumidification of space for water heating. The architecture of the system consists of (1) a plate and frame membrane-based absorber, (2) a membrane-based desorber and condenser unit, (3) heat exchangers, (4) ionic liquid, and (5) a 189.3 L (50-gal) water tank. The membrane-based absorber enables heat and mass transfer between three streams: moist air, ionic liquid, and the heat transfer fluid. The heat of vapor absorption elevates the ionic liquid temperature and, in turn, heats the heat transfer fluid. In the desorber unit, the diluted ionic liquid after absorption is heated to above 150℃ and reconcentrated. The heat of condensation from the condensation of water vapor in the condenser is utilized for water heating. The dehumidification performance of the absorber directly affects the COP and heating capacity of the system. Understanding the absorber's performance at various operating conditions would allow one to optimize and design a better performing absorber. In this study, the absorber's water heating capacity and performance are evaluated for varying operating conditions. A maximum COP of 1.25 while water heating water from 18.6 to 60.2°C was achieved at a capacity of 1,010 Watts and an airflow rate of 47.19 L/s. Increasing the desorber oil mass flowrate had negligible effect on the COP. The average mass transfer resistance of the porous membrane absorber was 1.164 *10 7 m/s.
Energy, 2017
Existing methods of drying fabrics involve energy-intensive thermal evaporation of moisture from ... more Existing methods of drying fabrics involve energy-intensive thermal evaporation of moisture from clothes. Drying fabrics using high-frequency vibrations of piezoelectric transducers can substantially reduce drying time and energy consumption. In this method, vibrational energy generates instability on the liquid-air interface and mechanically ejects water from a wet fabric. Here, for the first time, the physics of the ultrasonic fabric drying process in direct-contact mode is studied. The kinematic and thermal responses of water droplets and fabrics on piezoelectric crystal transducers and metal mesh-based transducers are studied. The results suggest that on piezoelectric crystal transducers, the response of a droplet subjected to ultrasonic excitation is dictated by the relative magnitude of the surface tension and the ultrasonic excitation forces. The drying process for a fabric on the studied transducers consists of two regimes-vibrational and thermal. When the water content is high, the vibrational forces can eject bulk water rapidly. But the more strongly bound water within the smaller fabric pores evaporates by the thermal energy generated as a result of the viscous losses. This study finds that a metal mesh-based transducer is more suitable for dewatering fabrics, as it facilitates the ejection of water from the fabric-transducer interface to the opposite side of the mesh. A demonstration unit developed consumes 10-20% of the water latent heat energy at water contents greater than 20%.
Renewable Energy, 2017
HIGHLIGHTS The performance of a novel thermally-driven semi-open sorption cycle is contrasted w... more HIGHLIGHTS The performance of a novel thermally-driven semi-open sorption cycle is contrasted with conventional absorption cycle performance. Unlike conventional systems, the semi-open cycle performance depends on ambient dry bulb and dewpoint temperatures. Under most conditions, semi-open cycle COP is slightly lower (1.3 to 1.5) than conventional (1.5 to 1.7). The semi-open system is capable of operation to very low dewpoint and dry bulb temperatures, though its performance suffers if both are low. Semi-open cycle performance under low ambient temperature can be improved with higher permeability, lower thermal conductivity membranes.
Langmuir : the ACS journal of surfaces and colloids, Jan 23, 2016
The mass transport capacity (i.e., the capillary limit,) of homogeneous wicks is limited by the i... more The mass transport capacity (i.e., the capillary limit,) of homogeneous wicks is limited by the inverse relation between the capillary pressure and permeability. Hybrid wicks with two or more distinct pore sizes have been proposed as alternative geometries to enhance the capillary limit. In this study, the impact of the two hybridization schemes-in-plane and out-of-plane-on the capillary transport of hybrid wicks is studied. Experimental data from in-plane hybrid wicks in conjunction with a theoretical model show that local changes in the curvature of the liquid-vapor meniscus (i.e., pore size) do not result in a higher mass flow rate than that of a comparable homogeneous wick. Instead, a global change in the curvature of the liquid-vapor meniscus (as occurring in out-of-plane hybrid wicks) is necessary for obtaining mass flow rates greater than that of a homogeneous wick. Therefore, the physics of capillary limit and dryout in out-of-plane hybrid wicks is investigated using a hybri...
IEEE Transactions on Components, Packaging and Manufacturing Technology, 2021
Thermal management is the current bottleneck in advancement of high-power integrated circuits (IC... more Thermal management is the current bottleneck in advancement of high-power integrated circuits (ICs), and phase change heat sinks are a promising solution. With a unique structural configuration consisting of a membrane positioned above the heater surface, membrane-based heat sinks (MHS) have thus far attained heat fluxes of up to 2 kW/cm 2 and HTC of up to 1.8 MW/m 2 K using water as the working fluid. This work reports the latest progress and performance evaluation of MHS for high flux thermal management. MHS is implemented in conjunction with a low surface tension liquid to rapidly expel bubbles from the heated surface and reach a CHF of 340 W/cm 2 and a HTC of 120 kW/m 2 K. A parametric comparison shows that thermal efficiency, defined as the ratio of cooling capacity and pumping power consumption, of the prototypical devices exceed values reported hitherto in literature by more than two orders of magnitude. Our results indicate that coupled with surfaces of higher thermal conductivity and membranes of higher permeability, MHS devices could be a promising solution to thermal management needs of high-power electronics and lasers.
Membrane biofouling has inhibited permselective separation processes for decades, requiring frequ... more Membrane biofouling has inhibited permselective separation processes for decades, requiring frequent membrane backwash treatment or replacement to maintain efficacy. However, frequent treatment is not viable for devices with a continuous blood flow such as a wearable or implantable dialyzer. In this study, the biofouling characteristics of a highly hemocompatible graphene oxide (GO) membrane developed through a novel self-assembly process is studied in a protein-rich environment and compared with performance of a state-of-the-art commercial polymer membrane dialyzer. The studies are conducted in phosphate-buffered saline (PBS) environment using human serum albumin (HSA), which represents 60% of the blood protein, at the nominal blood protein concentration of 1 g L-1. Protein aggregation on the membrane surface is evaluated by monitoring the change in the membrane flux and SEM imaging. The GO membrane water flux declined only ~10% over a week-long test whereas the polymer membrane fl...
To meet the growing energy consumption and mitigate climate concerns, novel energy efficient tech... more To meet the growing energy consumption and mitigate climate concerns, novel energy efficient technologies need to be developed. Water heating, dehumidification and space cooling form a significant percentage (~24%) of a typical U.S. household energy consumption and a total of 2.6 quad of primary energy consumption. In this paper, we present a novel system for combined water heating, dehumidification, and space cooling. The three processes can be achieved by one device using a novel semi-open absorption based system combined with evaporative cooling. The absorption based system absorbs water vapor from its ambient. The latent heat of absorption, released into the absorbent, is transferred into the process water that cools the absorbent. The water absorbed is later released in the desorber through heating, and the water vapor generated in the desorber is condensed and its heat of phase change is transferred to the process water in the condenser. The condensed water vapor can either be...
Physics of Fluids, 2021
The formation of thin liquid films around an elongated bubble moving in a capillary is pertinent ... more The formation of thin liquid films around an elongated bubble moving in a capillary is pertinent to many applications. However, development of a theoretical model for the film thickness has been a challenge for several decades. The prominent theory characterizing the film thickness was developed by Bretherton. This theory relates the liquid film thickness in axisymmetric capillaries to the flow capillary number (Ca) for values of up to 0.003. Modified forms of the Bretherton theory have been presented for Ca values as high as 2. However, the validity of these models has not been rigorously examined. In addition, the validity of Bretherton model itself in non-axisymmetric cross-section capillaries remains uncharted. The objective of this paper is to determine whether the Bretherton relation can be extended to a broader range of Ca values and non-axisymmetric crosssection channels, wherein the film thickness is not uniform along the channel circumference. A series of experiments are conducted on a set of fluids and different channel sizes and cross-sectional geometries to produce a wide range of viscous, surface tension, and inertial forces. The results show that when inertial forces are significant, modified Bretherton models fail to predict the film thickness at Ca well below 2. The experimental results also show that depending on fluid properties, another key requirement of Bretherton solution of Landau-Levich equation may not be met. In rectangular cross-section channels, the difference in surface tension forces along the longer and shorter channel axes, results in great deviation from the existing lubrication-based theories. This deviation greatly expands with increasing the channel aspect ratio. (3) 1 3 are the dimensionless coordinates obtained from the scale analysis (cf. Fig. 1A). Since there was no closed-form solution for the Landau
Scientific Reports, 2017
Nearly a century of research on enhancing critical heat flux (CHF) has focused on altering the bo... more Nearly a century of research on enhancing critical heat flux (CHF) has focused on altering the boiling surface properties such as its nucleation site density, wettability, wickability and heat transfer area. But, a mechanism to manipulate dynamics of the vapor and liquid interactions above the boiling surface as a means of enhancing CHF has not been proposed. Here, a new approach is implemented to limit the vapor phase lateral expansion over the heat transfer surface and actively control the surface wetted area fraction, known to decline monotonically with increasing heat flux. This new degree of freedom has enabled reaching unprecedented CHF levels and revealed new details about the physics of CHF. The impact of wickability, effective heat transfer area, and liquid pressure on CHF is precisely quantified. Test results show that, when rewetting is facilitated, the CHF increases linearly with the effective surface heat transfer area. A maximum CHF of 1.8 kW/cm2 was achieved on a copp...
Scientific Reports, 2017
Performance enhancement of the two-phase flow boiling heat transfer process in microchannels thro... more Performance enhancement of the two-phase flow boiling heat transfer process in microchannels through implementation of surface micro- and nanostructures has gained substantial interest in recent years. However, the reported results range widely from a decline to improvements in performance depending on the test conditions and fluid properties, without a consensus on the physical mechanisms responsible for the observed behavior. This gap in knowledge stems from a lack of understanding of the physics of surface structures interactions with microscale heat and mass transfer events involved in the microchannel flow boiling process. Here, using a novel measurement technique, the heat and mass transfer process is analyzed within surface structures with unprecedented detail. The local heat flux and dryout time scale are measured as the liquid wicks through surface structures and evaporates. The physics governing heat transfer enhancement on textured surfaces is explained by a deterministic...
International Journal of Refrigeration, 2016
In this study, the conjugate heat and mass transfer process taking place during the absorption of... more In this study, the conjugate heat and mass transfer process taking place during the absorption of a refrigerant vapor into a falling liquid film is analyzed using the Laplace transform method. The Laplace transform method has been previously utilized to model the process but under a uniform velocity profile assumption. Here, a more realistic linear velocity profile is employed. The results suggest that the uniform velocity profile assumption overestimates the refrigerant concentration across the liquid film, and underestimates the temperature profile and the vapor absorption rate. Overall, the uniform velocity profile assumption can result in up to 30% error in calculating the absorption rate. Using the new model, the effect of different flow parameters on the absorption rate has been studied. The efficacy of the model is demonstrated through comparison with various experimental and numerical results reported in the literature.
Applied Physics Letters, 2015
Volume 3: Advanced Fabrication and Manufacturing; Emerging Technology Frontiers; Energy, Health and Water- Applications of Nano-, Micro- and Mini-Scale Devices; MEMS and NEMS; Technology Update Talks; Thermal Management Using Micro Channels, Jets, Sprays, 2015
In this study, a new heat sink architecture is introduced that operates at two different phase ch... more In this study, a new heat sink architecture is introduced that operates at two different phase change heat transfer modes. At low wall superheat temperatures, the heat sink operates under the thin film evaporation heat transfer mode and then transitions to the boiling heat transfer mode when the wall superheat temperature increases. This unique function is enabled through constraining the liquid and vapor phases into separate domains using a capillary-controlled meniscus formed within a hierarchical 3D structure. The structure is designed to form thin liquid layers between vertically oriented menisci across which the liquid is evaporated into neighboring vapor channels. The entire structure is then capped by a hydrophobic vapor-permeable membrane to fully confine the liquid layers while allowing vapor to pass through the membrane. At low wall superheats, the liquid layers directly evaporate into the vapor channels. In this operation mode, the heat flux was linearly increased to a maximum of 54 W/cm 2 at approximately 8°C wall superheat temperature, corresponding to a heat transfer coefficient of approximately 62 kW/m 2 K. The heat transfer coefficient only slightly declined with increasing the wall superheat temperature but substantially improved as the liquid supply pressure was increased. Increasing the superheat temperature beyond 7-9°C resulted in transition to the boiling heat transfer mode with a pronounced increase in surface temperature fluctuations. This transition to boiling results in a decline in the heat transfer coefficient because the meniscus formed between the liquid and vapor spaces breaks down. However, the heat removal capacity is significantly increased, and a critical heat flux of about 300 W/cm 2 is reached at <30°C wall superheat temperature, corresponding to a heat transfer coefficient of approximately 100 kW/m 2 K.
Energy, 2015
In this study, microstructures are employed to manipulate thermohydraulic characteristics of the ... more In this study, microstructures are employed to manipulate thermohydraulic characteristics of the lithium bromide (LiBr) solution flow in a membrane-based absorber in order to enhance the absorption rate. In a membrane-based absorber, the liquid absorbent is constrained between a solid wall and a highly permeable membrane, thus facilitating manipulation of the flow properties. Recent numerical studies have shown that transport mode in a laminar flow can be changed from diffusive to advective via the implementation of surface microstructures on the flow channel walls. Here, we experimentally evaluate the enhancement in absorption rate caused by the introduction of microstructures on the solution flow channel wall of a membrane-based absorber. The experiments are conducted in a fully instrumented membrane-based absorption refrigeration system. The geometry and dimensions of the microstructures are based on the optimal values determined in our previous numerical studies. Absorption rates as high as that of a 100-µm-thick solution film (in the absence of wall features) is achieved but at two orders of magnitude less pressure drop. The achievement of a high absorption rate at a relatively low solution pressure drop in the proposed approach enhances the prospect of developing large-scale membrane-based absorbers.
International Journal of Heat and Mass Transfer, 2015
This work examines the microscale physics of the heat transfer events in flow boiling of FC-72 in... more This work examines the microscale physics of the heat transfer events in flow boiling of FC-72 in a microchannel. Experimental results discussed in this paper provide new physical insight on the nature of heat transfer events during bubbles growth and flow through the microchannel. The study is enabled through development of a device with a composite substrate that consists of a high thermal conductivity material coated by a layer of a low thermal conductivity material with embedded temperature sensors. This novel arrangement enables calculation of the local heat flux with a spatial resolution of 40-65 µm and a temporal resolution of 50 µs. The device generates isolated bubbles from a 300 nm in diameter artificial cavity fabricated at the center of a pulsed function micro-heater. Analysis of the temperature and heat flux data along with synchronized images of bubbles show that four mechanisms of heat transfer are active as a bubble grows and flows through the channel. These mechanisms of heat transfer are 1) microlayer evaporation, 2) interline evaporation, 3) transient conduction, and 4) micro-convection. Details of these mechanisms including their time period of activation and corresponding surface heat flux and heat transfer coefficient are extensively discussed. [17,23,28-30], their fundamental assumptions have not been examined due to the lack of necessary tools to probe the actual physics of the proposed mechanisms. These models are often constructed based on observations from overall trends in flow thermohydraulics characteristics as a function of externally controlled parameters (i.e. flow rate, heat flux, surface temperature, and fluid properties) as well as the observed flow regimes. The performance of
Energy, 2015
In this study, an absorber design suitable for the plate-and-frame absorber configuration is intr... more In this study, an absorber design suitable for the plate-and-frame absorber configuration is introduced. The design utilizes a fin structure installed on a vertical flat plate to produce a uniform solution film and minimize its thickness and to continuously interrupt the boundary layer. Using numerical models supported by experiments employing dye visualization, the suitable fin spacing and size and surface wettability are determined. The solution flow thickness is measured using the laser confocal displacement measurement technique. The new surface structure is tested in an experimental absorption system. A significantly high absorption rate (6 Â 10 À3 kg/m 2 s at a pressure potential of 700 Pa) is achieved in comparison with the conventional absorption systems. The effect of absorber water vapor pressure, solution flow rate, solution inlet concentration, cooling water inlet temperature and solution inlet temperature on the absorption rate is investigated. The proposed design provides a potential framework for development of highly compact absorption refrigeration systems.
International Journal of Multiphase Flow, 2014
The physics of water desorption from a lithium bromide (LiBr) solution flow through an array of m... more The physics of water desorption from a lithium bromide (LiBr) solution flow through an array of microchannels capped by a porous membrane is studied. The membrane allows the vapor to exit the flow and retains the liquid. Effects of different parameters such as wall temperature, solution and vapor pressures, and solution mass flux on the desorption rate were studied. Two different mechanisms of desorption are analyzed. These mechanisms consisted of: (1) direct diffusion of water molecules out of the solution and their subsequent flow through the membrane and (2) formation of water vapor bubbles within the solution and their venting through the membrane. Direct diffusion was the dominant desorption mode at low surface temperatures and its magnitude was directly related to the vapor pressure, the solution concentration, and the heated wall temperature. Desorption at the boiling regime was predominantly controlled by the solution flow pressure and mass flux. Microscale visualization studies suggested that at a critical mass flux, some bubbles are carried out of the desorber through the solution microchannels rather than being vented through the membrane. Overall, an order of magnitude higher desorption rate compare to a previous study on a membrane-based desorber was achieved.
Journal of Thermophysics and Heat Transfer, 2008
The heat-flux-based emissivity measurement technique developed in our earlier work has been used ... more The heat-flux-based emissivity measurement technique developed in our earlier work has been used to study the performance of an electrostatic switched radiator. The capability of fast and accurate measurement of the real-time changes in emissivity enabled by this technique allowed understanding of the transient behavior during activation, as well as identification of a major failure mode of the second-generation electrostatic radiator. A solution for resolution of this failure mode was then proposed and successfully tested, producing accurate and repeatable results over many cycles. A change in emissivity of 0.52 was achieved with 280 V applied, among the best consistent results achieved through electrostatic technology. The current work offers further understanding of electrostatic radiator performance and its application to space vehicles.
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Papers by saeed moghaddam