Liquid hydrogen line chilldown experiments at high Reynolds numbers. II. Analysis

Abstract This paper presents in-depth analysis of the recently conducted high Reynolds (Re) number liquid hydrogen (LH2) transfer line chilldown experiments at NASA Glenn Research Center. Vertically upward trickle and pulse flow chilldown tests were conducted over a wide range of LH2 liquid temperatures (20.3 K – 24.2 K) and mass flow rates (0.0012 – 0.036 kg/s) typical of a proposed cryogenic propellant depot. Two-phase flow mapping is used to correlate flow visualization with LH2 stream temperature profiles. Thermodynamic state diagrams, reverse boiling curves, and heat transfer coefficients are used to explain the evolution of the chill down process at various locations. Analysis reveals stark differences in behavior between skin and stream temperature measurements due to annular flow and bubbly flow dominated cooling. Analysis also shows that hydrogen chilldown at high Re numbers promotes better mixing and thus more liquid contact along the wall earlier on, in comparison to chilldown with other fluids like nitrogen where classical inverted annular flow boiling is incurred.