The Coupling Effect of Surface Vibration and Micro-structure on Spray Cooling Heat Transfer

Abstract

Although existing studies have emphasized the effects of micro-structured surfaces and vibration conditions on spray cooling efficiency. However, there is a research gap on how the coupling effect of these two factors affects spray cooling heat transfer. Therefore, in this study, the heat dissipation capacity of spray cooling under different vibration and microstructure size conditions is investigated experimentally using commercial HFE-649 as the coolant. The coolant is an electronic fluid with a global warming potential of only 1. Its low boiling point (49°C), which facilitates the early realisation of the phase change process, has a high potential for application in thermal management systems. The study reveals that both vibration and micro-structured surfaces significantly enhance the heat flux and heat transfer coefficient (HTC) in spray cooling. The combined effect of vibration and microstructures results in a more pronounced enhancement of cooling capacity, with the HTC increasing by 44% compared to a static smooth surface. As the vibration frequency and the side length ($w$) of the square fins on the micro-structured surface increase, the heat flux, HTC, critical heat flux (CHF), cooling efficiency, and heat transfer enhancement ratio (HTER) all show an increasing trend. However, at high vibration Reynolds numbers ($R{e}_v$) (15708) and the $w$ of the square fins of 0.8mm and 1.0mm, there is a notable decline in spray cooling capacity due to the excessively high $R{e}_v$ enhances the reciprocating motion of the liquid film, causing the film to inadequately spread and continuously accumulate around the edges. A correlation for heat dissipation capability of spray cooling under the coupled effects of vibration and micro-structured surfaces was derived and fitted, with the error in CHF within 12%.