In-Tank Thermodynamics of Slush Hydrogen for the National Aerospace Plane

Abstract

A series of fourteen pressurization and expulsion tests were performed with triple point and slush hydrogen in a horizontally positioned 1.9m3 (500-gallon) cryogenic tank. The tank was instrumented to determine temperature distribution in the ullage gas and liquid/slush. The pressurization gas was nominally 80K gaseous helium (GHe) and/or 300K gaseous hydrogen (GH). The test results showed that there were marked differences in pressurization performance between GHe and GH, and with liquid or slush hydrogen. Pressurization of slush hydrogen with warm GH was much more rapid and efficient than with cold GHe. In addition, GHe pressurization of slush hydrogen took twice as long as pressurization of triple point hydrogen, while GH pressurization of triple point and slush hydrogen took about the same time. Pre-pressurization and expulsion pressurization using GH resulted in substantial ullage pressure collapse at initiation of expulsion (possibly due to surging in the warm outflow line leading to interface disruption and ullage condensation). Conversely, pre-pressurization with cold GHe, followed by expulsion pressurization with warm GH, appeared to suppress GH condensation and eliminate ullage pressure collapse at expulsion. The test data were successfully correlated using a multi-node one-dimensional pressurization/stratification code which accounts for real fluid properties, ullage/liquid condensation/evaporation, stratification and heat transfer.