Experimental study on heat transfer characteristics of phase change by liquid nitrogen spray cooling

Liquid nitrogen spray cooling, which uses liquid nitrogen as the cooling medium, has certain differences from traditional room-temperature spray cooling. A semi-closed phase change cooling experimental platform for liquid nitrogen spray was established to test the cooling effect of liquid nitrogen spray on heating surfaces. It addresses the adiabatic issues and moisture interference of liquid nitrogen spray in open systems, while avoiding the impact of high pressure from rapidly expanding nitrogen on the experiment. The test bench enables regulation of different heating conditions, as well as precise adjustment of parameters such as nozzle flow rate, spray chamber pressure, and spray height, facilitating experiments on the influencing factors of spray-cooled surfaces. The research shows that: The maximum heat flux density of this semi-closed liquid nitrogen spray cooling system reaches 284 W·cm⁻², with a corresponding surface superheat of 33.8 K. Changes in environmental and structural parameters have little impact on the range of the high-efficiency heat transfer zone of liquid nitrogen spray cooling, which is basically stable between 50 W·cm⁻² and 150 W·cm⁻². The low viscosity and low surface tension of liquid nitrogen enable the liquid nitrogen spray-cooled surface to achieve higher superheat and heat flux density, referred to as “critical heat flux (CHF) hysteresis” in this study. When approaching critical heat flux, changes in environmental and structural parameters do not significantly affect the surface heat transfer coefficient as they do for the maximum surface heat transfer coefficient. Instead, the surface heat transfer coefficient at the onset of CHF under various operating conditions falls within the range of 70 to 90 W·m⁻²·K⁻¹.