Numerical investigation of liquid nitrogen spray cooling under low ambient pressure

Due to the high heat dissipation rate of electronic devices and the lack of heat sink in hypersonic spacecraft, thermal management of high-power electronic devices poses serious challenges. Liquid nitrogen spray cooling (LNSC) exhibits the advantages of high cooling capacity and small system volume, and shows promising potential in electronic device cooling in spacecraft. This study established a two-phase boiling numerical model of LNSC based on the Euler–Lagrange method. The validated numerical model was used to simulate the heat transfer and flow of LNSC under low ambient pressures ranging from 20 kPa to 100 kPa at the nozzle heights varying from 5 mm to 20 mm. The effects of low ambient pressures and nozzle heights on the average wall temperature, wall temperature distribution, surface temperature non-uniformity (STNU), and wall film flow characteristics were investigated. It shows that as the ambient pressure decreases, the average wall temperature increases to the highest value at the ambient pressure of 60 kPa, and then decreases. While STNU shows the oscillational ascending trend, exhibiting 29.085 % increase at 20 kPa comparing with that at 100 kPa. Considering the effects of nozzle heights, it indicates that as the nozzle height decreases, the average wall film velocity initially increases to the highest value of 0.134 m/s, and then decreases afterwards, while the average wall film thickness continues to increase. Moreover, with the increase of the nozzle height, the average wall temperature decreases to the lowest value, and then increases, concluding that the optimal nozzle height is 10 mm. The findings of this research provide a theoretical basis for thermal management design in aerospace applications.