Two-stage bubble point pressure: A newly found feature of Dutch Twill weave porous screen

The porous screen is a vital material in the area of in-orbit propellant management, due to its efficient performance to separate gas and liquid in microgravity conditions. Among the diversities of screens, the Dutch Twill weave (DTW) screen is the most commonly used owing to its extensive adaptability of different fluids including storable and cryogenic propellants. This study focuses on the bubble point pressure (BPP), a quite important characteristic parameter of the screen applied to gas-liquid separation. It has been commonly considered by previous researchers that BPP for a given working fluid and fixed screen structure has a certain value. However, the two-stage-bubble-point pressure phenomenon that was newly found in an experiment reveals three new parameters of DTW screens: the first order BPP, the second order BPP, and the critical depressurizing level. After a bubble breakthrough occurs, only if the driving pressure is decreased to under the critical depressurizing level, can the screen be fully resealed; otherwise, the screen can be just partially resealed. For the pressurization beginning at the fully resealed state, the critical value of the driving pressure to trigger a bubble breakthrough is the first order BPP; but for the pressurization beginning at the partially resealed state, the critical value becomes the second order BPP. To understand this phenomenon, we analyzed the microstructure of DTW screens and then reconstructed the conceptual model of screen pore, according to the distribution mode of pore diameter. The new model explain the phenomenon by introducing three special character parameters: the first order BPP, the second order BPP, and the critical depressurizing level, which are corresponding to the locations of the first throat, the second throat, and the abdomen in a pore passage, respectively. The detailed mechanism was quantitatively illustrated by a CFD simulation. The discovery of this feature of DTW screens should be a meaningful reminder that after bubble breakthrough occurs, only when the driving pressure is decreased to below the critical depressurizing level, can the original performance of screen be recovered fully.