Research on the Diffusion and Deposition Characteristics of Refrigerant Under Vertical Upward Leakage in a Confined Space

In a confined space, the flammability of alternative refrigerants (such as R717, R290, R32, and R1234yf) poses significant safety risks during leaks. However, in the actual refrigeration systems, the direction of refrigerant leakage is difficult to predict, complicating explosion risk assessment. In this work, R717, R290, R32, and R1234yf were selected as the research objects to analyze the diffusion process and deposition characteristics of different refrigerants leaking vertically upward into a confined space, and to explore the migration characteristics of flammable refrigerants under different leakage amounts and flammability area in a confined space. The results show that after vertical upward leakage, the refrigerants tend to impact the top wall and then move along the top wall away from the leak source. High-density refrigerants diffuse primarily near the floor, while less dense refrigerant diffuses along the top and side wall of the space. After the refrigerant leakage stops, R1234yf, with the highest density, exhibited the most pronounced deposition, with the highest concentration near the floor and the lowest at the top (1.69% and 0.7%, respectively). Conversely, lower-density refrigerants showed decreasing floor concentrations and increasing top concentrations, with reduced overall deposition. Compared to the deposition concentration of R290 at the bottom of the room (1.32%), R744 demonstrated higher deposition near the floor than R290, likely due to its higher viscosity at similar densities. In addition, using R290 as an example, the study reveals that the increase in leakage amount and the prolonged time result in a gradual expansion and upward diffusion of the flammability area, encompassing the top of the space, walls, and floor.