Experimental study on performance characteristics of a −70 °C ultra-low temperature medical freezer with mixed hydrocarbon refrigerant

It is well-known that the −70 °C ultra-low temperature freezers have been widely concerned for vaccine and biomedical products storage due to the outbreak of COVID-19. This paper carries out the experimental investigation on performance characteristics of a −70 °C ultra-low temperature medical freezer with single-stage Joule-Thomson refrigeration system by using binary hydrocarbon mixture R601a/R1150 and ternary mixture R601a/R290/R1150. The aim is to explore and verify hydrocarbon refrigerants that can achieve lower energy consumption, thereby providing a scientific basis for the optimization of ultra-low temperature medical freezers. The experimental results show that both R601a/R1150 and R601a/R290/R1150 with a charge of 250 g could achieve the refrigeration temperature below −70 °C in a 568 L large volume vertical freezer. Comparing binary with ternary refrigerants, it is found that the addition of medium-boiling component R290 is beneficial to reduce the daily energy consumption. When the mass fraction of R601a/R1150 is 0.70/0.30, the lowest daily energy consumption for −70 °C is 9.06 kW h·24 h⁻¹. When the mass fraction of the R601a/R290/R1150 is 0.70/0.10/0.20, the daily energy consumption is 8.42 kW h·24 h⁻¹, which is 7.06 % lower than that when using the R601a/R1150. This indicates that careful selection of refrigerant components and composition optimization can lead to substantial energy savings. Furthermore, it is also observed that among these three components, the low-boiling component R1150 has the most significant influence on the system pressures and operating power, followed by R601a and R290.