Experimental study on liquid nitrogen flash evaporation spray on super-hydrophilic microstructured surface

Abstract

Flash evaporation spray is an efficient heat transfer method. Changes in the microstructure and wettability of the cooling surface have important effects on its heat transfer. In this paper, four kinds of cooling surfaces, including a smooth copper surface, a square-column microstructured surface, a superhydrophilic smooth surface, and a superhydrophilic square-column surface, were prepared by chemical corrosion and laser etching. Using liquid nitrogen as the cooling medium, we conducted transient flash evaporation spray experiments on these four types of cooling surfaces. The experimental results show that surface superhydrophilic treatment can substantially enhance the flash evaporation spray of liquid nitrogen. It can more than double the cooling rate for both smooth copper surfaces and square-column microstructured surfaces. In addition, the combination of a microcolumn structure and superhydrophilicity on the cooling surface can provide double reinforcement for the liquid nitrogen flash evaporation spray. Its average cooling rate can reach 131,046 °C/min, and the maximum heat flux is 173 W/cm2. This study sheds some lights on heat transfer mechanism of superhydrophilic microstructure on the flash evaporation spray and contributes to the development of a new method for cell vitrification.