Warm pressurant gas bubble point experiments for coarse mesh screen channel liquid acquisition devices in liquid nitrogen

Abstract

The most crucial aspect in screen channel liquid acquisition device (LAD) design is the bubble point pressure (ΔPBP). Historically, results have shown that cryogenic liquid nitrogen (LN2) ΔPBP values can be increased when using helium (GHe) pressurant and decreased when using gaseous nitrogen (GN2) pressurant due to evaporative cooling and condensation heating of the liquid-vapor interface within the screen, respectively. Historical results show a reduction in ΔPBP performance when using warm pressurant, regardless of pressurant gas type. This paper presents warm pressurant ΔPBP tests in LN2 using both GHe and GN2 with pressurant bulk gas temperatures TGB between 77−160K for 14 screen types, focusing on coarser meshes. Results from this study show a degradation in GHeΔPBP but no degradation in GN2ΔPBP at elevated TGB, the latter of which contradicts historical trends. To help explain these results and to provide a level of physical background to the warm pressurant ΔPBP experiments, a noncondensable pressurant sweat cooling heat and mass transfer model is developed as part of this study. Based on current and historical results, it is concluded that the flow velocities on the gas side of the screen could degrade ΔPBP significantly, especially when warm pressurant is used.