Liquid temperature gradient estimation for screen channel liquid acquisition device bubble point tests in liquid nitrogen

Abstract

The LAD screen utilizes surface tension forces in microgravity environments to allow liquid to flow through the screen while blocking vapor ingestion up to a certain pressure differential across the screen. The limiting pressure differential of LAD screen operation prior to bubble breakthrough is known as the bubble point pressure (ΔPBP). Previous cryogenic ΔPBP studies have identified how noncondensable pressurization decreases the interface temperature within the pores of a LAD screen via evaporative cooling and how autogenous pressurization increases the interface temperature within a LAD screen via condensation heating. The temperature gradient in the liquid side boundary layer near the screen caused by these effects has not been previously quantified. This study provides an order of magnitude analysis to show how certain variables can influence the liquid side temperature gradient during ΔPBP tests in liquid nitrogen (LN2) using noncondensable pressurization. Furthermore, cryogenic LN2ΔPBP data is taken for a 325x2300 Dutch Twill and 200x600 Dutch Twill screen with liquid side temperature measurements collected at varying distances away from the screen using dewar pressures ranging from ∼0-8psig (∼101.3-156.5kPa absolute). It has been shown that measuring the liquid screen side temperature 1/8″ (3.2 mm) away from the screen can result in a liquid side surface tension value that is ∼10-12.5% lower than the actual surface tension value at the interface for GHe tests in LN2. An empirical correlation is provided based on experimental temperature gradient data to correct historical and future ΔPBP data for the liquid screen side diode placement.