Performance investigation of the CO₂ gas cooler designs and its integration with the refrigeration system

In CO₂ refrigeration systems, the system can operate in subcritical or transcritical cycle depending on ambient temperature. When the system is operating in transcritical cycle the heat exchanger at the high-pressure side of the system is well known as gas cooler. The gas cooler rejects heat from the superheated refrigerant gas to ambient air without condensation in single phase heat transfer process. The understanding of its performance parameters under different conditions and control strategies is essential to adequately design and optimise for specific applications. In this paper, a detailed mathematical model is developed in the Engineering Equation Solver (EES) platform, and validated with experimental results obtained from a test rig at the National Centre for Sustainable Energy use in Food Chains (CSEF). The model is investigated two different gas cooler designs when separately installed and test into a CO₂ refrigeration system, an attempt to formulate the design guidelines for CO₂ gas coolers. Then the detailed gas cooler models were integrated with the CO₂ refrigeration system model to investigate the effects of the gas cooler design into system COP. Parameters such as intermediate pressure, evaporating temperature and cooling capacity were defined from the experimental results and then inserted to the model. The results of the detailed gas cooler model and CO₂ refrigeration system model were validated against the experimental test results based on the gas cooler performance and overall system performance.