多孔结构毛细抽吸模型及实验验证

Development and Experimental Verification of Capillary Pumping Model for Porous Structure

建立了多孔结构(毛细芯)毛细抽吸的数学模型,推导毛细抽吸量随时间变化的关系式,并用实验对其进行验证。结果表明,毛细芯抽吸工质时,其抽吸量按照指数增长的规律变化,该指数增长函数的初始值大小等于工质密度、毛细芯横截面积、孔隙率和高度的乘积,幅值为负数,其大小一般略小于初始值,二者的比值可视为多孔结构饱和程度的度量,时间常数的大小则等于工质密度、毛细芯相对渗透率和孔隙率的比值以及重力加速度的乘积的倒数。即抽吸量(体积)取决于毛细芯总孔隙体积的大小,而抽吸的快慢则与工质密度、毛细芯相对渗透率和孔隙率的比值成正比。传统的观点认为毛细芯提供的毛细力和渗透率均越大越好,但两者却是矛盾的,毛细抽吸性能可视为它们二者的综合平衡。

The capillary pumping model for porous structure （porous wick） was developed. The relation between capillary pumping amount and time was found and verified by experiment. The result shows that the changing of capillary pumping amount of porous structure accords with an exponential increase equation. The offset value of the equation is equal to the power of density of the working fluid, porosity, height and cross sectional area of the porous wick, and the amplitude is negative and its value is usually a little smaller than the offset value and their ratio can be regarded as the saturation degree of the porous structure. Besides, time constant of the exponential increase equation, which represents the rapidness or tardiness of the capillary pumping, is equal to the reciprocal value of the power of density of the working fluid, relative permeability and porosity of the porous wick and acceleration of gravity. That is to say, the capillary pumping amount （volume） is determined by the total volume of the pores in the porous structure; the capillary pumping rate is proportional to the density of the working fluid and the ratio of relative permeability and porosity of the porous wick in the gravity field. It is used to considering that both capillary force and permeability of the wick are the bigger the better; however, they are antinomy, and the capillary pumping performance can be considered as the best balance of them.