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Amir Faghri - One of the best experts on this subject based on the ideXlab platform.
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Experimental investigation on loop thermosyphon thermal performance with flow visualization
International Journal of Heat and Mass Transfer, 2020Co-Authors: Sara Kloczko, Amir FaghriAbstract:Abstract A non-phase change heat pipe (NPCHP) with no wick was proposed as a new heat pipe which is not dependent on a wick or phase change at steady state operation and where the heat transfer is driven by the pressure response to a heat input, rather than phase change. It was shown recently that the NPCHP is not a new heat pipe as suggested but is a loop thermosyphon (Kloczko et al., 2019). This effort focuses on understanding how changing different system parameters, including heat input, fill ratio, inclination angle, and working fluid affects the overall system performance of both the single-phase and two-phase loop Thermosyphons. Flow visualization is incorporated and the flow of liquid/vapor through the thermosyphon is studied. Depending upon the initial fill ratio of the loop thermosyphon and the working fluid, the thermosyphon is shown to either operate as a two-phase loop thermosyphon or a single-phase loop thermosyphon.
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economic evaluation of latent heat thermal energy storage using embedded Thermosyphons for concentrating solar power applications
Solar Energy, 2011Co-Authors: Christopher W. Robak, Theodore L. Bergman, Amir FaghriAbstract:Abstract An economic evaluation of a latent heat thermal energy storage (LHTES) system for large scale concentrating solar power (CSP) applications is conducted. The concept of embedding gravity-assisted wickless heat pipes (Thermosyphons) within a commercial-scale LHTES system is explored through use of a thermal network model. A new design is proposed for charging and discharging a large-scale LHTES system. The size and cost of the LHTES system is estimated and compared with a two-tank sensible heat energy storage (SHTES) system. The results suggest that LHTES with embedded Thermosyphons is economically competitive with current SHTES technology, with the potential to reduce capital costs by at least 15%. Further investigation of different phase change materials (PCMs), thermosyphon working fluids, and system configurations has the potential to lead to designs that can further reduce capital costs beyond those reported in this study.
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Economic evaluation of latent heat thermal energy storage using embedded Thermosyphons for concentrating solar power applications
Solar Energy, 2011Co-Authors: Christopher W. Robak, Theodore L. Bergman, Amir FaghriAbstract:An economic evaluation of a latent heat thermal energy storage (LHTES) system for large scale concentrating solar power (CSP) applications is conducted. The concept of embedding gravity-assisted wickless heat pipes (Thermosyphons) within a commercial-scale LHTES system is explored through use of a thermal network model. A new design is proposed for charging and discharging a large-scale LHTES system. The size and cost of the LHTES system is estimated and compared with a two-tank sensible heat energy storage (SHTES) system. The results suggest that LHTES with embedded Thermosyphons is economically competitive with current SHTES technology, with the potential to reduce capital costs by at least 15%. Further investigation of different phase change materials (PCMs), thermosyphon working fluids, and system configurations has the potential to lead to designs that can further reduce capital costs beyond those reported in this study. ?? 2011 Elsevier Ltd.
A J Robinson - One of the best experts on this subject based on the ideXlab platform.
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confinement and vapour production rate influences in closed two phase reflux Thermosyphons part a flow regimes
International Journal of Heat and Mass Transfer, 2018Co-Authors: Kate Smith, R Kempers, A J RobinsonAbstract:Abstract This study investigates the boiling regimes in a small diameter (D = 8 mm) transparent thermosyphon. The influence of confinement on the boiling regimes was studied using a range of fluids. The confinement of the vapour phase leads to boiling regimes that differ from those traditionally described for thermosyphon evaporator boiling physics, widely considered as a combination of pool boiling and film evaporation. The boiling behaviour of small dimension Thermosyphons was investigated by designing and constructing a fully transparent thermosyphon, enabling simultaneous thermal and visual analysis. Three working fluids, water, ethanol and HFE-7000, were used to characterise the thermosyphon behaviour with varied characteristic bubble length scales. The observed flow regimes could be characterised in terms of the degree of confinement and rate of vapour production. A flow regime map was developed based on these observations to predict thermosyphon flow in terms of both confinement and the rate of vapour production. It was determined that for low confinement and high rates of vapour production, the boiling regimes resemble those of pool boiling. In contrast, at high levels of confinement and high heat flux, an unsteady regime exists where relatively large bubbles and vapour generation rates result in a pulsatile geyser-type flow regime.
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experimental investigation of small diameter two phase closed Thermosyphons charged with water fc 84 fc 77 and fc 3283
Applied Thermal Engineering, 2010Co-Authors: Hussam Jouhara, A J RobinsonAbstract:Abstract An experimental investigation of the performance of Thermosyphons charged with water as well as the dielectric heat transfer liquids FC-84, FC-77 and FC-3283 has been carried out. The copper thermosyphon was 200 mm long with an inner diameter of 6 mm, which can be considered quite small compared with the vast majority of Thermosyphons reported in the open literature. The evaporator length was 40 mm and the condenser length was 60 mm which corresponds with what might be expected in compact heat exchangers. With water as the working fluid two fluid loadings were investigated, that being 0.6 ml and 1.8 ml, corresponding to approximately half filled and overfilled evaporator section in order to ensure combined pool boiling and thin film evaporation/boiling and pool boiling only conditions, respectively. For the Fluorinert™ liquids, only the higher fill volume was tested as the aim was to investigate pool boiling opposed to thin film evaporation. Generally, the water-charged thermosyphon evaporator and condenser heat transfer characteristics compared well with available predictive correlations and theories. The thermal performance of the water-charged thermosyphon also outperformed the other three working fluids in both the effective thermal resistance as well as maximum heat transport capabilities. Even so, FC-84, the lowest saturation temperature fluid tested, shows marginal improvement in the heat transfer at low operating temperatures. All of the tested Fluorinert™ liquids offer the advantage of being dielectric fluids, which may be better suited for sensitive electronics cooling applications and were all found to provide adequate thermal performance up to approximately 30–50 W after which liquid entrainment compromised their performance.
David Astrain - One of the best experts on this subject based on the ideXlab platform.
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Experimental and computational study on thermoelectric generators using Thermosyphons with phase change as heat exchangers
Energy Conversion and Management, 2017Co-Authors: María Araiz, David Astrain, A. Martínez, Patricia ArangurenAbstract:An important issue in thermoelectric generators is the thermal design of the heat exchangers since it can improve their performance by increasing the heat absorbed or dissipated by the thermoelectric modules. Due to its several advantages, compared to conventional dissipation systems, a thermosyphon heat exchanger with phase change is proposed to be placed on the cold side of thermoelectric generators. Some of these advantages are: high heat-transfer rates; absence of moving parts and lack of auxiliary consumption (because fans or pumps are not required); and the fact that these systems are wickless. A computational model is developed to design and predict the behaviour of this heat exchangers. Furthermore, a prototype has been built and tested in order to demonstrate its performance and validate the computational model. The model predicts the thermal resistance of the heat exchanger with a relative error in the interval [−8.09; 7.83] in the 95% of the cases. Finally, the use of Thermosyphons with phase change in thermoelectric generators has been studied in a waste-heat recovery application, stating that including them on the cold side of the generators improves the net thermoelectric production by 36% compared to that obtained with finned dissipators under forced convection.
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development of a thermoelectric refrigerator with two phase Thermosyphons and capillary lift
Applied Thermal Engineering, 2009Co-Authors: J. G. Vián, David AstrainAbstract:Abstract A thermoelectric domestic refrigerator has been developed, with a single compartment of 0.225 m 3 , for food preservation at 5 °C. The cooling system is made up of two equal thermoelectric devices, each composed of a Peltier module (50 W) with its hot side in contact with a two-phase and natural convection thermosyphon (TSV) and a two-phase and capillary lift thermosyphon (TPM), in contact with the cold side. The entire refrigerator has been simulated and designed using a computational model, based on the finite difference method. Subsequently an experimental optimization phase of the Thermosyphons was carried out, until thermal resistance values of R TSV = 0.256 K/W and R TPM = 0.323 K/W were obtained. These values were lower than those obtained with finned heat sinks. Finally, a functional prototype of a thermoelectric refrigerator was built, and the results which were obtained demonstrate that it is able to maintain a thermal drop (Ambient Temperature–Inside Temperature) of 19 °C. The electric power consumption at nominal conditions was 45 W, reaching a COP value of 0.45. The study demonstrated that by incorporating these two-phase devices into thermoelectric refrigeration increases the COP by 66%, compared with those which use finned heat sinks.
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Development of a thermoelectric refrigerator with two-phase Thermosyphons and capillary lift
Applied Thermal Engineering, 2009Co-Authors: J. G. Vián, David AstrainAbstract:A thermoelectric domestic refrigerator has been developed, with a single compartment of 0.225 m3, for food preservation at 5 °C. The cooling system is made up of two equal thermoelectric devices, each composed of a Peltier module (50 W) with its hot side in contact with a two-phase and natural convection thermosyphon (TSV) and a two-phase and capillary lift thermosyphon (TPM), in contact with the cold side. The entire refrigerator has been simulated and designed using a computational model, based on the finite difference method. Subsequently an experimental optimization phase of the Thermosyphons was carried out, until thermal resistance values of RTSV= 0.256 K/W and RTPM= 0.323 K/W were obtained. These values were lower than those obtained with finned heat sinks. Finally, a functional prototype of a thermoelectric refrigerator was built, and the results which were obtained demonstrate that it is able to maintain a thermal drop (Ambient Temperature-Inside Temperature) of 19 °C. The electric power consumption at nominal conditions was 45 W, reaching a COP value of 0.45. The study demonstrated that by incorporating these two-phase devices into thermoelectric refrigeration increases the COP by 66%, compared with those which use finned heat sinks. © 2008 Elsevier Ltd. All rights reserved.
Evelyn N. Wang - One of the best experts on this subject based on the ideXlab platform.
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modeling and optimization of hybrid solar thermoelectric systems with Thermosyphons
Solar Energy, 2011Co-Authors: Nenad Miljkovic, Evelyn N. WangAbstract:Abstract We present the modeling and optimization of a new hybrid solar thermoelectric (HSTE) system which uses a thermosyphon to passively transfer heat to a bottoming cycle for various applications. A parabolic trough mirror concentrates solar energy onto a selective surface coated thermoelectric to produce electrical power. Meanwhile, a thermosyphon adjacent to the back side of the thermoelectric maintains the temperature of the cold junction and carries the remaining thermal energy to a bottoming cycle. Bismuth telluride, lead telluride, and silicon germanium thermoelectrics were studied with copper–water, stainless steel–mercury, and nickel–liquid potassium thermosyphon-working fluid combinations. An energy-based model of the HSTE system with a thermal resistance network was developed to determine overall performance. In addition, the HSTE system efficiency was investigated for temperatures of 300–1200 K, solar concentrations of 1–100 suns, and different thermosyphon and thermoelectric materials with a geometry resembling an evacuated tube solar collector. Optimizations of the HSTE show ideal system efficiencies as high as 52.6% can be achieved at solar concentrations of 100 suns and bottoming cycle temperatures of 776 K. For solar concentrations less than 4 suns, systems with thermosyphon wall thermal conductivities as low as 1.2 W/mK have comparable efficiencies to that of high conductivity material Thermosyphons, i.e. copper, which suggests that lower cost materials including glass can be used. This work provides guidelines for the design, as well as the optimization and selection of thermoelectric and thermosyphon components for future high performance HSTE systems.
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Modeling and optimization of hybrid solar thermoelectric systems with Thermosyphons
Solar Energy, 2011Co-Authors: Nenad Miljkovic, Evelyn N. WangAbstract:We present the modeling and optimization of a new hybrid solar thermoelectric (HSTE) system which uses a thermosyphon to passively transfer heat to a bottoming cycle for various applications. A parabolic trough mirror concentrates solar energy onto a selective surface coated thermoelectric to produce electrical power. Meanwhile, a thermosyphon adjacent to the back side of the thermoelectric maintains the temperature of the cold junction and carries the remaining thermal energy to a bottoming cycle. Bismuth telluride, lead telluride, and silicon germanium thermoelectrics were studied with copper-water, stainless steel-mercury, and nickel-liquid potassium thermosyphon-working fluid combinations. An energy-based model of the HSTE system with a thermal resistance network was developed to determine overall performance. In addition, the HSTE system efficiency was investigated for temperatures of 300-1200. K, solar concentrations of 1-100 suns, and different thermosyphon and thermoelectric materials with a geometry resembling an evacuated tube solar collector. Optimizations of the HSTE show ideal system efficiencies as high as 52.6% can be achieved at solar concentrations of 100 suns and bottoming cycle temperatures of 776. K. For solar concentrations less than 4 suns, systems with thermosyphon wall thermal conductivities as low as. 1.2. W/mK have comparable efficiencies to that of high conductivity material Thermosyphons, i.e. copper, which suggests that lower cost materials including glass can be used. This work provides guidelines for the design, as well as the optimization and selection of thermoelectric and thermosyphon components for future high performance HSTE systems. © 2011 Elsevier Ltd.
Christopher W. Robak - One of the best experts on this subject based on the ideXlab platform.
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economic evaluation of latent heat thermal energy storage using embedded Thermosyphons for concentrating solar power applications
Solar Energy, 2011Co-Authors: Christopher W. Robak, Theodore L. Bergman, Amir FaghriAbstract:Abstract An economic evaluation of a latent heat thermal energy storage (LHTES) system for large scale concentrating solar power (CSP) applications is conducted. The concept of embedding gravity-assisted wickless heat pipes (Thermosyphons) within a commercial-scale LHTES system is explored through use of a thermal network model. A new design is proposed for charging and discharging a large-scale LHTES system. The size and cost of the LHTES system is estimated and compared with a two-tank sensible heat energy storage (SHTES) system. The results suggest that LHTES with embedded Thermosyphons is economically competitive with current SHTES technology, with the potential to reduce capital costs by at least 15%. Further investigation of different phase change materials (PCMs), thermosyphon working fluids, and system configurations has the potential to lead to designs that can further reduce capital costs beyond those reported in this study.
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Economic evaluation of latent heat thermal energy storage using embedded Thermosyphons for concentrating solar power applications
Solar Energy, 2011Co-Authors: Christopher W. Robak, Theodore L. Bergman, Amir FaghriAbstract:An economic evaluation of a latent heat thermal energy storage (LHTES) system for large scale concentrating solar power (CSP) applications is conducted. The concept of embedding gravity-assisted wickless heat pipes (Thermosyphons) within a commercial-scale LHTES system is explored through use of a thermal network model. A new design is proposed for charging and discharging a large-scale LHTES system. The size and cost of the LHTES system is estimated and compared with a two-tank sensible heat energy storage (SHTES) system. The results suggest that LHTES with embedded Thermosyphons is economically competitive with current SHTES technology, with the potential to reduce capital costs by at least 15%. Further investigation of different phase change materials (PCMs), thermosyphon working fluids, and system configurations has the potential to lead to designs that can further reduce capital costs beyond those reported in this study. ?? 2011 Elsevier Ltd.