Experimental and Numerical Investigation on Critical Heat Flux and Cooling Efficiency of Liquid Nitrogen Spray Cooling

With continuously growing heat loads of microelectronic and aerospace equipment, spray cooling stands out as an effective high-heat-flux thermal management technology. Though room-temperature spray cooling has been extensively explored, liquid nitrogen spray cooling, a competitive cryogenic cooling approach, still lacks clear parametric laws and heat transfer limits due to harsh and unstable low-temperature test conditions. In this paper, experiments are carried out on a semi-closed liquid nitrogen spray cooling test rig to investigate how spray flow rate, chamber pressure and spray height affect the critical heat flux (CHF) and cooling efficiency of heated surfaces. Experimental results reveal that the maximum CHF reaches 284 W·cm−2. Increasing flow rate raises the heat transfer limit but cuts cooling efficiency, while both CHF and efficiency are barely sensitive to chamber pressure. The spray height enabling full wall coverage is optimal, delivering a peak cooling efficiency of 32.9%. The simulation explains the relationship between liquid film evolution and CHF/cooling efficiency. Simulations demonstrate that liquid film thickness rises first and then decreases moderately with growing spray height, inconsistent with the conventional view that thinner films yield superior heat transfer. The findings provide useful guidance for the design and optimization of cryogenic spray cooling systems.