| Micro refrigeration systems are being increasingly used nowadays. One example is electronic cooling. With the rapid advancement of chips, traditional passive heat dissipation techniques are becoming obsolete and hence, new active cooling techniques become necessary. The other example is the personal thermal comfort system demanded by people working in the hazardous environment, such as fire fighting. Among various cooling methods, Vapor Compression Refrigeration (VCR) is the most promising method. According literatures, however, few miniature refrigeration systems are available.;This thesis presents two Miniature Vapor Compression Refrigeration (MVCR) systems, one for electronics cooling and the other for personal thermal comfort. In particularly, following aspects are focused: 1) Thermodynamic analysis. The thermodynamic models of the systems are developed and the performances are studied under various working conditions including compressor efficiencies, ambient temperature and so on. 2) Entropy analysis. It is found that entropy of the compressor and the heat leakage play crucial roles. High efficient compressor and the heat leakage minimization are very important. 3) Prototype building. Two prototypes are built: one for electronics cooling and the other for personal thermal comfort. The miniature compressors are purchased from market. The heat exchangers, including the cold pate, tube-fin evaporator and micro channel condenser, are custom designed and made. 4) Experiment testing. The two prototypes are tested under various working conditions such as compressor speed, refrigerant charge and capillary tube length. For the electronics cooling system, the cold plate temperature could be maintained at about 60 ºC under the 200 W heater power input. The second-law efficiency of the system varies from 0.23 to 0.31; and the compressor efficiency is between 40% ~ 65%. For the personal thermal comfort system, its capacity could reach 321 W with 100 g refrigerant charge, 1200 mm capillary tube length, and the compressor speed of 4503 rpm. The COP is 4.59 and the second-law efficiency is between 0.21 ~ 0.27. The performances of the two systems are comparable to that of the current domestic refrigeration systems. Therefore, it is expected that they will find some practical applications in the near future. |
