Heat transfer of a capillary evaporator in a loop heat pipe was analyzed through 3D numerical simulations to study the effects of the thermal conductivity of the wick, the contact area between the casing and the wick,...Heat transfer of a capillary evaporator in a loop heat pipe was analyzed through 3D numerical simulations to study the effects of the thermal conductivity of the wick, the contact area between the casing and the wick, and the subcooling in the compensation chamber (CC) on the thermal performance of the evaporator. A pore network model with a distribution of pore radii was used to simulate liquid flow in the porous structure of the wick. To obtain high accuracy, fine meshes were used at the boundaries among the casing, the wick, and the grooves. Distributions of temperature, pressure, and mass flow rate were compared for polytetra-fluoroethylene (PTFE) and stainless steel wicks. The thermal conductivity of the wick and the contact area between the casing and the wick significantly impacted thermal performance of the evaporator heat-transfer coefficient and the heat leak to the CC. The 3D analysis provided highly accurate values for the heat leak;in some cases, the heat leaks of PTFE and stainless steel wicks showed little differences. In general, the heat flux is concentrated at the boundaries between the casing, the wick, and the grooves;therefore, thermal performance can be optimized by increasing the length of the boundary.展开更多
Objective To prevent the maldistribution of two phase refrigerant in dry expansion evaporators composed of parallel coils, a distributor is needed to supply refrigerant into the coils. Methods A simplified model of...Objective To prevent the maldistribution of two phase refrigerant in dry expansion evaporators composed of parallel coils, a distributor is needed to supply refrigerant into the coils. Methods A simplified model of dry expansion evaporator was proposed. The flow and heat transfer in distributing pipes and evaporator coils were simulated with a numerical method. Results The heat flow rate decreases while the refrigerant is distributed unequally to evaporator coils. Conclusion In order to maintain the heat flow rate, larger heat transfer area should be arranged to make up the effect of maldistribution. The larger the discrepancy of mass flow rate is, the more heat transfer area is needed.展开更多
The disturbance, caused by the boiling Phenomena in the inverted meniscus ac evaporator, is of great importancein the normal operation of the CPL, especially When the heat load is low. By theoretical and experimental ...The disturbance, caused by the boiling Phenomena in the inverted meniscus ac evaporator, is of great importancein the normal operation of the CPL, especially When the heat load is low. By theoretical and experimental studies onthis issue, it shows that the evaporator of the CPL operates in a mode of boiling in the Wick. By solving a set ofmomentum equations, it concludes that, this kind of boiling Phenomena in the wick cause no notable negativeinfluence on the normal peiformance of the CPL, although there really edests some adVerse influence during theCPL start-up. Addihonally, the causes of the dry-out of the evaporator under low heat load are conducted in thepaper. The conclusions are verified by subsequent experiments. More details about the experiments are alsodescribed in the paper.展开更多
This paper presents the experimental investigation on the heat transfer chaxacteristics in inverted evaporator of Micro/Miniature Capillary Pumped Loop (MCPL). The evaporation heat transfer coefficients as a function ...This paper presents the experimental investigation on the heat transfer chaxacteristics in inverted evaporator of Micro/Miniature Capillary Pumped Loop (MCPL). The evaporation heat transfer coefficients as a function of the heat flux density, the geometrical sizes of capillary wick structure and the vapor grooves are shown. Qualitative analysis of the heat transfer characteristics of the inverted evaporator of MCPL is also made.展开更多
An overall two-dimensional numerical model of the miniature flat plate capillary pumped loop （CPL） evaporator is developed to describe the liquid and vapor flow, heat transfer and phase change in the porous wick str...An overall two-dimensional numerical model of the miniature flat plate capillary pumped loop （CPL） evaporator is developed to describe the liquid and vapor flow, heat transfer and phase change in the porous wick structure, liquid flow and heat transfer in the compensation cavity and heat transfer in the vapor grooves and metallic wall. The entire evaporator is solved with SIMPLE algorithm as a conjugate problem. The effect of heat conduction of metallic side wall on the performance of miniature flat plate CPL evaporator is analyzed, and side wall effect heat transfer limit is introduced to estimate the performance of evaporator. The shape and location of vapor-liquid interface inside the wick are calculated and the influences of applied heat flux, liquid subcooling, wick material and metallic wall material on the evaporator performance are investigated in detail. The numerical results obtained are useful for the miniature flat plate evaporator performance optimization and design of CPL.展开更多
文摘Heat transfer of a capillary evaporator in a loop heat pipe was analyzed through 3D numerical simulations to study the effects of the thermal conductivity of the wick, the contact area between the casing and the wick, and the subcooling in the compensation chamber (CC) on the thermal performance of the evaporator. A pore network model with a distribution of pore radii was used to simulate liquid flow in the porous structure of the wick. To obtain high accuracy, fine meshes were used at the boundaries among the casing, the wick, and the grooves. Distributions of temperature, pressure, and mass flow rate were compared for polytetra-fluoroethylene (PTFE) and stainless steel wicks. The thermal conductivity of the wick and the contact area between the casing and the wick significantly impacted thermal performance of the evaporator heat-transfer coefficient and the heat leak to the CC. The 3D analysis provided highly accurate values for the heat leak;in some cases, the heat leaks of PTFE and stainless steel wicks showed little differences. In general, the heat flux is concentrated at the boundaries between the casing, the wick, and the grooves;therefore, thermal performance can be optimized by increasing the length of the boundary.
文摘Objective To prevent the maldistribution of two phase refrigerant in dry expansion evaporators composed of parallel coils, a distributor is needed to supply refrigerant into the coils. Methods A simplified model of dry expansion evaporator was proposed. The flow and heat transfer in distributing pipes and evaporator coils were simulated with a numerical method. Results The heat flow rate decreases while the refrigerant is distributed unequally to evaporator coils. Conclusion In order to maintain the heat flow rate, larger heat transfer area should be arranged to make up the effect of maldistribution. The larger the discrepancy of mass flow rate is, the more heat transfer area is needed.
文摘The disturbance, caused by the boiling Phenomena in the inverted meniscus ac evaporator, is of great importancein the normal operation of the CPL, especially When the heat load is low. By theoretical and experimental studies onthis issue, it shows that the evaporator of the CPL operates in a mode of boiling in the Wick. By solving a set ofmomentum equations, it concludes that, this kind of boiling Phenomena in the wick cause no notable negativeinfluence on the normal peiformance of the CPL, although there really edests some adVerse influence during theCPL start-up. Addihonally, the causes of the dry-out of the evaporator under low heat load are conducted in thepaper. The conclusions are verified by subsequent experiments. More details about the experiments are alsodescribed in the paper.
文摘This paper presents the experimental investigation on the heat transfer chaxacteristics in inverted evaporator of Micro/Miniature Capillary Pumped Loop (MCPL). The evaporation heat transfer coefficients as a function of the heat flux density, the geometrical sizes of capillary wick structure and the vapor grooves are shown. Qualitative analysis of the heat transfer characteristics of the inverted evaporator of MCPL is also made.
文摘An overall two-dimensional numerical model of the miniature flat plate capillary pumped loop （CPL） evaporator is developed to describe the liquid and vapor flow, heat transfer and phase change in the porous wick structure, liquid flow and heat transfer in the compensation cavity and heat transfer in the vapor grooves and metallic wall. The entire evaporator is solved with SIMPLE algorithm as a conjugate problem. The effect of heat conduction of metallic side wall on the performance of miniature flat plate CPL evaporator is analyzed, and side wall effect heat transfer limit is introduced to estimate the performance of evaporator. The shape and location of vapor-liquid interface inside the wick are calculated and the influences of applied heat flux, liquid subcooling, wick material and metallic wall material on the evaporator performance are investigated in detail. The numerical results obtained are useful for the miniature flat plate evaporator performance optimization and design of CPL.
