Literature review of R744 mixtures for heating and cooling application and future prospective for their CFD multiphase modelling

Carbon dioxide is increasingly recognized as a sustainable alternative refrigerant for heating and cooling systems due to its low global warming potential (GWP = 1) and favourable thermophysical properties. However, carbon dioxide-based systems face certain challenges, particularly lower efficiency at high ambient temperatures. To overcome these limitations, researchers have explored carbon dioxide mixtures with other refrigerants, such as dimethyl ether, propane, and others. These mixtures show potential for improved performance while maintaining a low environmental impact. As a result, they have garnered significant interest in both industrial and academic sectors, particularly for applications in refrigeration, air conditioning, and heat pump systems. This review provides an in-depth examination of carbon dioxide mixtures, focusing on their thermodynamic properties, performance in various heating and cooling applications, and the latest experimental and theoretical advances. Special emphasis is placed on the role of Computational Fluid Dynamics (CFD) in modelling the behaviour of these mixtures during phase transitions. Two-phase flow modelling is especially critical for carbon dioxide mixtures, as phase changes, such as boiling and condensation, play a significant role in system performance. Accurate CFD modelling of these two-phase flows is essential for a deeper understanding of heat transfer, pressure drop, and overall fluid dynamics. Advanced CFD techniques, including the Volume of Fluid (VOF) method, have demonstrated potential for simulating two-phase flows. However, very few studies, if any, have comprehensively analysed carbon dioxide mixtures using CFD, highlighting a gap in the current research.