Experimental study on liquid sodium capillary dynamics in screen wicks

Abstract

As an indispensable structure in heat pipe, the capillary characteristics of screen wick directly affect the circulating behavior of working medium and the overall heat transfer performance of heat pipe. In this paper, the capillary characteristics of stainless steel screen wick and molybdenum screen wick with high temperature liquid sodium as working medium are tested by capillary rising method combined with weighing method. The variations of wick mass and immersion height with changing temperatures for different types of wire mesh wicks are explored from experimental measurement and model prediction. In the first heating period, the sodium wettability and wick mass are significantly improved when heating to about 460 °C. The variations of wick mass are in opposite trend with temperatures in the subsequent cycles of heating and cooling, which indicates that the damage of surface oxide layer by chemical reaction is irreversible. The sodium capillarity in screen wick mainly depends on the mesh number and interlayer spacing, while the layer number impose little effect on the results. The molybdenum screen wick presents out the better capillary performance than stainless steel screen wick. The predictions of maximum heights and wick mass at different temperatures from capillary model are compared with experimental data. It is found that the error of calculated sodium mass in wick are within 12 %.