Leakage, diffusion and distribution characteristics of refrigerant in a limited space:A comprehensive review

The leakage and direct emission of high GWP HFC refrigerants in refrigeration, air-conditioning and heat pump systems increase the greenhouse effect, which pose huge threats to the ecological environment and the human health. Meanwhile, some alternative refrigerants with excellent environmental performance have different degrees of flammability. When the flammable refrigerants catastrophically leak from the refrigeration system into a limited space, it is easy to cause an explosion accident, the safety of people and property in the space is greatly threatened. In addition, the operating conditions of refrigeration systems, thermophysical properties of the refrigerants, obstacles and ventilation conditions of the space have a great impact on the process of refrigerant leakage and diffusion, the explosion risks formed in the external space have certain differences. To promote the security application of the alternative refrigerants, the leakage, diffusion, and distribution characteristics of the refrigerants from both theoretical and experimental aspects were reviewed in this work. The potential causes of leakages and common types of leakage holes in refrigeration systems were summarized, and the advantages and disadvantages of the existing leakage and diffusion theoretical models were concluded. The impact of the micro-sized leakage of the refrigerant on the internal of the system was discussed. The diffusion and distribution of the refrigerants in the external space after they catastrophically leaked from different types of systems were analyzed, and the influence of different parameters on the refrigerant distribution and the explosion risk based on the catastrophic leakage was also presented. The future work was prospected. The review is expected to provide a valuable reference for the safety risk assessment of the flammable refrigerants.