Experimental and theoretical investigation on the performance of CO2/propane auto-cascade refrigerator with a fractionation heat exchanger

This paper proposed a small-sized auto-cascade refrigeration cycle using CO2/propane as the refrigerant. A fractionation heat exchanger (FHEX) was introduced into this cycle to improve the separation efficiency of CO2 and propane. The effect of FHEX on the performance of the cycle was analyzed. And the comparison between with and without FHEX was presented based on the experiment and numerical simulation data at the cooling water inlet temperature of 18.3 °C. Results show that the evaporating temperatures of the cycle with FHEX are 9.1–20.3 °C lower than that of the cycle without FHEX with the increase of CO2 mass fraction from 0.22 to 0.31. The corresponding refrigeration capacity, power input and COP have 37.1–61.7%, 24.7–36.8% and 16.4–42.7% reduction, respectively. The further computation results of different vapor quality in FHEX at the condensing temperature of 23.3 °C and 37.0 °C indicate that reducing the vapor quality causes an enhancement in the separation of CO2 and propane, and thus decreases the evaporating temperature. Moreover, all of the refrigeration capacity, power input and COP are decreased. It is concluded that the cycle performance would be improved by increasing CO2 mass fraction or decreasing the cooling water temperature.