Thermodynamic Analysis of Transcritical Carbon Dioxide Cycles

Abstract

Research on natural environmentally friendly refrigerants is very important especially because the world-wide agreement about restriction in the use of ozone depleting refrigerants. Carbon dioxide is a natural refrigerant that has been considered for certain refrigeration and air conditioning applications. The aim of this paper is to present a thermodynamic analysis of carbon dioxide cycles in order to evaluate the potential performance of a refrigeration cycle using carbon dioxide. A thermodynamic model for the cycle is developed which can simulate the operation of a carbon dioxide refrigeration/AC cycle. This model takes into account the practical effects of the thermo-physical properties of carbon dioxide as refrigerant in a trans-critical cycle. A sensitivity analysis has been conducted so that cycle performance is estimated. The cooling load, compressor power, and coefficient of performance (C.O.P.) were evaluated. One and two stages of compression were also considered for comparison purposes. Cycle performance was evaluated based on variation of important parameters such as evaporator, intermediate, and discharge pressures. The effects of cycle components on system capacity and cycle performance are also investigated. Comparison between performances of the CO2 cycle and the standard vapor compression cycle is performed. Thermodynamic calculations showed reasonable agreement with available experimental data based on the general assumptions made.