Development of a flow boiling visualization experiment for liquid hydrogen

Abstract Liquid hydrogen (LH 2 ) is the highest specific impulse rocket fuel and used on roughly 25% of active United States rocket launch systems. However, these systems are informed by flow boiling heat transfer correlations, the most recent of which has up to 50% root-mean-squared error when used with liquid hydrogen. These errors are exacerbated by the fact that no previous experiments have optically verified multiphase hydrogen flow regimes concurrent with heat transfer measurements. To address this gap, this publication presents the development of a two-phase hydrogen visualization flow cell that can address uncertainty in existing models by providing temperature, velocity, and pressure drop data while identifying flow regimes in two-phase hydrogen. Preliminary results using liquid nitrogen are provided with uncertainties. The resulting system will be used to characterize boiling and heat transfer criticality for increased confidence in multi-phase liquid hydrogen flow estimates for system design.