Hydraulic and heat transfer characteristics of slush hydrogen in a circular pipe under terrestrial and microgravity conditions

Slush hydrogen is a mixture of solid hydrogen and liquid hydrogen, Compared with pure liquid hydrogen, it can be used as the fuel of rocket and space booster due to its densified feature. In the present study, a numerical model is built based on the Eulerian-Eulerian model and the kinetic theory of granular flow to investigate the hydraulic and heat transfer characteristics of slush hydrogen in a circular pipe under both terrestrial and microgravity conditions. The numerical model is first validated by the experimental results reported in the literature. The flow of slush hydrogen with different inlet velocities and solid volume fractions are numerically studied to investigate the solid volume fraction distribution and velocity profile of the outlet cross-section. Considering the transportation of slush hydrogen in practical applications, the hydraulic characteristics of slush hydrogen in an inclined pipe under terrestrial condition and in a horizontal pipe under microgravity are also investigated. The results show significant influence of the gravity on the solid volume fraction distribution and pressure drop of slush hydrogen. The heat transfer of slush hydrogen is also studied, which shows that the temperature of fluid can be locally decreased sufficiently using slush hydrogen such that the vaporization of liquid hydrogen can be suppressed. Solid hydrogen particle with small diameter can improve heat transfer between the solid phase and liquid phase, and the melting of solid hydrogen is accelerated. It is clarified that the increases of both the inlet velocity and solid volume fraction show positive effects on the local heat transfer coefficient. (C) 2017 Elsevier Ltd. All rights reserved.