Ground-based near-space-oriented spray cooling: Temperature uniformity analysis and performance prediction

Thermal control systems in near-space-oriented vehicles are bound to be different from those on either traditional airplanes or typical space shuttles owing to the extremely thin atmosphere caused by the high altitude and awfully hot air produced by the aerodynamic heat. The tough thermal environment encountered by the vehicle will pose great challenges for the thermal control system deployed in the near-space platform, which is hazardous for the onboard electrodriven equipment. Therefore, it is imperative to invent a novel cooling scheme for the reliable operation of the device. For thermally protecting the onboard permanent magnet synchronous motor in a rudder cabin, a novel largespace spray cooling system was proposed in a previous study by Wang, J. X., Li, Y. Z., Yu, X. K., Li G. C., and Ji, X. Y. ("Investigation of Heat Transfer Mechanism of Low Environmental Pressure Large-Space Spray Cooling for Near-space Flight System," International Journal of Heat and Mass Transfer, Vol. 119, April 2018, pp. 496-507); based on which, a further study of the experimental data is conducted in this paper. Temperature uniformities within the small-scaled motor and among different motors are studied, and strategies for enhancing the temperature uniformity among motors are proposed. In addition, thermal predictions of the small-scaled permanent magnet synchronous motor for both of the flash-boiling subcooled regimes using the backpropagation neural network are developed. A maximum relative error of ±7% is observed, which illustrates the superiority of the current model as compared with the fitting correlation developed in the previous study.