The effect of gravity on cryogenic transfer line chilldown performance using pulse flow and low thermally conductive coatings

Abstract

Future cryogenic propulsion systems will require efficient methods to chill down transfer lines and propellant tanks prior to transfer of 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, depending on mission constraints and desires. This paper examines an efficiency parameter based on a simplified energy balance that can be used to compare the performance 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 nitrogen line chilldown experiments conducted in both terrestrial and microgravity to compare efficiencies between numerous continuous and pulse chilldown tests on bare as well as coated tubes across a range of thermodynamic conditions. Despite a well-known reduction in heat transfer in microgravity due to the absence of buoyancy-assisted cooling, results indicate no appreciable degradation in chilldown efficiency at moderate-to-high Reynolds numbers in microgravity relative to terrestrial gravity.