Enhancement of heat transfer on micro- and macro- structural surfaces in close-loop R410A flashing spray cooling system for heat dissipation of high-power electronics

High effective spray cooling system is urgently required for the thermal management of high-power electronics in small areas. These electronic devices need to be cooled at functional operating temperature, and it is particularly lacking in current spray cooling studies. For this purpose, a hybrid structural surface that integrates micro- roughness and macro- structure is investigated in close-loop R410A flash spray cooling system. The heat transfer performance is tremendously enhanced as the increase of roughness on flat surface until it reaches the value of 3.5 μm. Meanwhile, a novel tetrahedral fin surface is proposed and compared with modified surfaces including flat, wavy, square, and pyramid fins. It performs high heat flux of 411.2 W cm⁻², a 101.5 % enhancement over the flat surface. What's more, the hybrid structure with 3.5 μm roughness can further improve the maximum critical heat flux and heat transfer coefficient by up to 424 W cm⁻² and 814 kW K⁻¹ m⁻², respectively, while keeping the surface temperature below 50 °C. Besides, correlations and energy efficiency are studied to explore the performance of structural surfaces. These findings in a wider range of roughness and macrostructure will provide insights to guide the surface modification in flash spray cooling.