关键词: 多孔介质, 泡破压力, 有效孔径, 分离, 孔隙尺度

Abstract:

The metal porous mesh screen has many advantages such as large specific surface area and good physical stability, and is widely used in the fields of propellant on-orbit gas-liquid separation and phase change heat transfer. Bubble point pressure is the most important parameter governing the separation performance, which is determined by the effective bubble point diameter of the porous material. The effective pore diameter can be estimated through experimental measurements, whereas experimental methods require measurements of several working fluids for each specification of porous mesh. Owing to the experimental limitations, scanning electron microscopy (SEM) analysis is proposed to estimate the pore diameter from SEM images. However, it is proven to be unreliable since the 2D images cannot account for the complex pore structures of the wire mesh. The prediction of bubble point pressure remains a challenge. Herein, this paper presents an analytical model of bubble point pressure for metal wire mesh considering the effect of pore structures. Variation of the effective flow area during the bubble breakthrough is detailed analyzed based on the 3D model of the porous wire mesh. The effective pore diameter is quantified by analogy to a capillary tube, which is expressed as a function of mesh parameters, including the intervals, diameters, relative angle and turn angle of the mesh wires. Each parameter is determined solely from the pore-scale morphology, and hence, the accurate expression for each mesh is derived without introducing any fitting constants. In addition, bubble point pressure measurements are conducted. The predicted effective pore diameters from the proposed model are corroborated by 7 specifications of porous mesh from existing literature and current experiments with a mean absolute relative error of 8%. Moreover, more than 250 data points of bubble point pressure are collected from open literature, focusing on both room-temperature and cryogenic fluids. The applicability of the present analytical model on different mesh specifications and various fluids are validated with the relative error smaller than 10%. The results further verify the validity of the bubble point model based on Young-Laplace equation, which considered the porous media to be analogous to a bundle of capillary tubes. This work deepens the understanding on the periodical porous structures of the wire mesh and proposed an analytical model to predict the bubble point pressure, which breaks free from the experimental limitations.

Key words: porous medium, bubble point pressure, effective pore diameter, separation, pore-scale