Comparison of Several Zero-Boil-Off Pressure Control Strategies for Cryogenic Fluid Storage in Microgravity

Abstract

Four different tank pressure control strategies based on various combinations of active cooling and/or forced mixing are investigated numerically. The first, and most effective, strategy uses a subcooled liquid jet to simultaneously mix and cool the bulk liquid. The second strategy is based on separate mixing and cooling via a forced uncooled liquid jet and an independent cold finger. The third strategy uses a cold finger alone with no forced mixing. Finally, the fourth strategy examines the effect of mixing alone without any active cooling. Detailed numerical solutions are obtained for each case by solving the Navier―Stokes and energy equations in the liquid region coupled to a lumped heat and mass treatment of the vapor region. It is shown that the most rapid and effective means of countering self-pressurization is achieved with a subcooled liquid jet. In the case of separate mixing and cooling, the pressure can still be reduced, but over a much longer period of time. Finally, cooling without any forced mixing is able to limit the pressure rise, but not very effectively, although for long-duration storage in which rapid pressure control is not required, this may still constitute a viable approach. While presenting the results of the various simulation case studies, an in-depth comparative analysis of transport phenomena associated with each case is also performed from which salient engineering recommendations are derived for optimization of the zero-boil-off design.