Modelling of a Two-Phase Thermosyphon Loop for Passive Air-Conditioning of a House in Hot and Dry Climate Countries

The two-phase thermosyphon loop is an efficient solution for space cooling. This paper presents the simulation results of numerical studies on the heat transfer and thermal performance of a two-phase thermosiphon loop for passive air-conditioning of a house. The fluid considered in this study is methanol, which is compatible with copper and is environmentally friendly. These numerical results show that the temperature at the evaporator wall drops from 23°C to 13°C and increases at the condenser. The solar flux density has a strong influence on the condenser temperature. The mass flow rates and masses at the evaporator and condenser increase with temperature. The variation of evaporating and condensing temperature affects the performance of the system. For a constant evaporating and condensing temperature of 2°C and 29°C, the COP is 0.77 and 0.84 respectively. With these results, the use of the two-phase thermosyphon loop in air conditioning is possible to obtain a thermal comfort of the occupants acceptable by the standards but with a large exchange surface of the evaporator.

Operating Characteristics of Multiple Evaporators and Multiple Condensers Loop Heat Pipe with Polytetrafluoroethylene Wicks

This paper presents fabrication and testing of a multiple-evaporator and multiple-condenser loop heat pipe (MLHP) with polytetrafluoroethylene (PTFE) porous media as wicks. The MLHP has two evaporators and two condensers in a loop heat pipe in order to adapt to various changes of thermal condition in spacecraft. The PTFE porous media was used as the primary wicks to reduce heat leak from evaporators to compensation chambers. The tests were conducted under an atmospheric condition. In the tests that heat loads are applied to both evaporators, the MLHP was stably operated as with a LHP with a single evaporator and a single condenser. The relation between the sink temperature and the thermal resistance was experimentally evaluated. In the test with the heat load to one evaporator, the heat transfer from the heated evaporator to the unheated evaporator was confirmed. In the heat load switching test, in which the heat load is switched from one evaporator to another evaporator repeatedly, the MLHP could be stably operated. The loop operation with the large temperature difference between the heat sinks was also tested. From this result, the stable operation of the MLHP in the various conditions was demonstrated. It was also found that a flow regulator which prevents the uncondensed vapor from the condensers is required at the inlet of the common liquid line when one condenser has higher temperature and cannot condense the vapor in it.

Experimental study on dynamic behavior of mechanically pumped two-phase loop with a novel accumulator in simulated space environment

Mechanically pumped two-phase loop(MPTL)which is a prominent two-phase heat transfer technology presents a promising prospect in thermal control for space payload.However,transient behavior of MPTL caused by phase-change and heat sources load-on/off in simulated space environment is rarely reported.In the present study,one MPTL setup was designed and constructed,and experimentally studied.Particularly,a novel two-phase thermally-controlled accumulator integrated with passive cooling measure and three capillary structures was designed as the temperature-control device.Dynamic behavior of the start-up,temperature control,and temperature adjustment were monitored;meanwhile,thermodynamic behavior within the proposed accumulator,the operating behavior as well as the heat and mass transfer behavior between the main loop and the accumulator were revealed.The results show that the fluid management function of the capillary structures for the novel accumulator is verified.The working point of the MPTL system can be adjusted by changing the temperature control point of the accumulator and it is little influenced by external heat flux and heat sources on/off.Pressure-drop oscillations which are manifested as fluctuations of temperature and pressure can be observed after phase changing due to the compressible volume within the accumulator and the negative-slope portion of the internal pressure.

微型热驱动回路的脉动及位差对热性能的影响

以甲醇为工质,采用高速数据采集系统测定了微型热驱动回路在不同运行参数下的压力及温度脉动,其脉动周期及脉动幅度随蒸发段热流密度的增加而减小。实验发现,在蒸发段热流密度较低的情况下,蒸气管中是泡状流或弹状流交替存在,而在蒸发段热流密度较高时,蒸气管中为环状流,就位差对热性能的影响进行了详细的实验研究,并在冷凝器空气自然对流和强迫对流情况下,以加热块温度90℃为上限,得出微通道蒸发器和冷凝器在不同位差下的最大蒸发段热流密度,通过对实验现象的观察及分析,以期开发出适用于未来电子产品高功率需求的微型化电子冷却器。