Liquid hydrogen line chilldown experiments at high Reynolds Numbers. Optimal chilldown methods

Abstract

Future cryogenic propulsion systems will require efficient methods to chill down propellant tanks and transfer lines prior to transfer of precious propellant while in space. When chilling down the transfer line, there is an inherent tradeoff between propellant mass consumed and chilldown time to steady state. This paper proposes a parameter based on a simplified energy balance that can be used to compare the efficiency of different chilldown methods and to determine the optimal chilldown method. The parameter, along with chilldown time and mass, is then applied to recent liquid hydrogen (LH2) line chilldown experiments conducted at NASA Glenn to compare efficiencies between numerous trickle and pulse chilldown tests across a wide range of LH2 temperatures and mass flow rates. Secondary parameters such as heat transfer coefficient, minimum pressure drop, and number of valve cycles are also considered for completeness.