Computational analysis of a transcritical CO2 refrigeration cycle with and without an ejector

Due to increasingly stringent environmental policies and the urgent need for environmentally friendly refrigerants with zero ozone depletion potential (ODP) and negligible global warming potential (GWP), carbon dioxide CO2 has emerged as a primary natural alternative. However, the low efficiency of conventional transcritical CO2 refrigeration cycles under high ambient temperatures, particularly in hot climates, remains a major technical challenge. Among the technologies proposed to improve system performance, ejectors have attracted significant attention due to their ability to recover part of the expansion work, thereby reducing the compressor pressure ratio and enhancing the coefficient of performance (COP). Unlike most studies in the literature that analyze the ejector as an isolated component, this work presents a comprehensive thermodynamic simulation of a complete transcritical CO2 refrigeration cycle with the ejector fully integrated. A modular modeling framework was developed in Python using REFPROP, in which all system components are described through mass, energy, and linear momentum balances and are coupled to capture their mutual interactions at the system level. Heat exchangers are modeled using one-dimensional distributed discretization, allowing geometric effects on temperature and pressure distributions to be considered while maintaining a low computational cost. The overall simulation time is approximately two hours per operating condition. Model predictions show good agreement with available experimental data. For the ejector, the constant pressure mixing model provides higher accuracy than the 1D double choking model. Numerical results indicate that the integration of the ejector leads to COP improvements between 22% and 25% compared with the conventional transcritical cycle, demonstrating the effectiveness of the proposed modeling approach for evaluating high-performance CO2 refrigeration systems operating in hot climates.