Experimental study on system performance of ultra-low temperature cascade refrigeration system using Carbon Dioxide with tapered evaporator/sublimator

CO₂ has received extensive attentions in developing various energy conversion systems. In recent years, a CO₂ ultra-low temperature cascade refrigeration system with dry ice sublimation has been introduced. The system is composed of two CO₂ refrigeration compression cycles, namely high pressure cycle and low pressure cycle, to achieve a cryogenic refrigeration bellow the CO₂ triple-point temperature of -56.6℃. In the expansion process of the liquid CO₂ at the low pressure cycle, dry ice (solid-gas two-phase flow) is formed, and it has been know that the geometric configuration of the evaporator/sublimator is one of important factors in the CO₂ ultra-low temperature cascade refrigeration system.
In this report, a tapered evaporator/sublimator is newly designed and installed into the existed CO₂ ultra-low temperature cascade refrigeration system in order to investigate the heat transfer characteristics and its associated system performances. Based on the investigation, it is found that the CO₂ ultra-low temperature cascade refrigeration system with the tapered evaporator/sublimator has the capability of achieving the ultra-low temperature of -66.3℃ continuously. Resultantly the achieved refrigeration temperature with the tapered evaporator/sublimator is 3.5℃ lower than that of the sudden expansion evaporator/sublimator which is installed in the previous system.