Simulation and Performance Evaluation of Trans-Critical CO₂ Refrigeration System Integrated with Spray-Cooled Gas Coolers

Abstract

Rising ambient temperatures pose significant challenges to the thermodynamic performance of trans-critical CO₂ refrigeration systems, as they reduce system efficiency and cooling capacity. To mitigate these adverse effects, a spray-cooling technique was employed to enhance the heat rejection process. A mathematical model of the spray-cooled gas cooler, employing a homogeneous-mixture assumption that treats air and water droplets as a single phase without velocity slip or temperature difference, was developed and validated against experimental data. The developed model was subsequently integrated into the refrigeration system model to evaluate the system’s performance with an air temperature range of 30 °C to 40 °C. The results show that spray cooling effectively decreases the CO2 pressure and temperature exiting the gas cooler, lowers the compressor power consumption, enhances the evaporator cooling capacity, and significantly improves the overall system performance. The results also indicate that increasing the spray-water-to-air-mass flow rate ratio beyond around 0.075 yields negligible gains. Under conditions of air temperature of 40 °C, air velocity of 2 m/s and spray-water temperature of 25 °C, the coefficient of performance increased from 1.53 to 2.74, the heat rejection rate rose by 9.8%, the cooling capacity improved by 33.3%, and the compressor power consumption decreased by 25.9% as the spray-water-to-air-mass flow rate ratio increased from 0.02 to 0.075.