The prediction for optimum combination of high pressure and intermediate pressure on a small refrigerated cabinet with CO2 transcritical two-stage cycle

Abstract

It is universally acknowledged that the use of two-stage cycle can effectively improve the comprehensive performance of the CO2 refrigeration system. There exists an optimum combination of high pressure and intermediate pressure in a CO2 refrigeration system with transcritical two-stage cycle where the system yields the best coefficient of performance (COP). In this paper, a novel double-iteration method is used to predict the optimum combination of high pressure and intermediate pressure of a CO2 refrigerated cabinet system with transcritical two-stage cycle and the accuracy of prediction is experimentally verified. Then, the validated thermodynamic model is employed to identify the calculation accuracies of related existing correlations for calculating the optimum high pressure and the optimum intermediate pressure under various conditions. The results show that the thermodynamic model has enough accuracy to predict the optimum combination of high and intermediate pressures with an error less than 2.07%. Among the several major existing correlations, ′′Sarkar + Yari′′ (-10 °C≤Te≤10 °C, 30 °C≤Tgc,o≤50 °C) display the most accurate results to calculate the combination of high and intermediate pressures of a CO2 transcritical cycle. Meanwhile, the difference of thermodynamic performance predicted by the model and ′′Sarkar + Yari′′ correlations can be negligible (approximate to 0).