Study On A New Auto-Cascade Refrigerating Cycle

Low-temperature refrigerating cascade systems are widely used in preservation of biological tissues, cooling detectors, cryosurfaces and providing circumstances for material and component testing. In this thesis, the performance of a new Auto Cascade Refrigeration Cycle (ACR) is studied both experimentally and theoretically.The research and development history in the field of Auto Cascade Refrigeration Cycle is reviewed. Contrast to some traditional cascaded cycles and ACRs, a new ACR that employs a rectifying column is proposed.Environment-friendly non-azeotropic refrigerant mixture (NARM) is used as working fluid. The rectifying column is employed to separate high boiling component, low boiling component and lubricant. A rig was designed on the basis of thermodynamic analysis. Some factors, including mixture composition, cycle compression ratio and suction ratio of circumfluence fluid of the rectifying column, are analyzed of their impacts on coefficient of performance.An experimental apparatus has been set up and experiments have been carried out successfully. It is the first time to use a kind of environment-friendly refrigerant, a rectifying column and an air-conditioning compressor in the ultra-low temperature refrigeration cycle. High boiling component, low boiling component and lubricant can be separated effectively. The temperature in the ultra-low temperature box can reach below -80癈. The performance of Auto Cascade Refrigeration Cycle at different operation modes is investigated. According to a series of experimental data, the effect of following factors on the temperature in the ultra-low temperature box and COP are analyzed: the mixture composition, the pressure ratio and the return fluid extraction ratio of the rectifying column, the refrigeration capacity and the flow rate through throttle valve. The results of this thesis are of great importance for further research.