Hydrogen particles in liquid helium Original Research Article

Numerical investigations of phase changes during the generation of solid hydrogen particles in cryogenic helium, which include vaporization and re-condensation of helium around a hydrogen droplet and solidification of the droplet in helium, are conducted to unravel the basic mechanisms underlying the phase change phenomena. In a single-fluid, two-phase mixture framework, the simulation of vaporization/condensation involves a vapor–liquid exchange model that accounts for mass and energy transfers due to phase changes between liquid and vapor helium. The enthalpy-porosity, solidification–melting technique is employed to investigate the hydrogen solidification. The volume fraction of each phase in the solidification process is determined using a volume of fluid (VOF) two-phase model, along with a piecewise-linear approach to trace the liquid/solid interface. The results throw some light on the helium flow field resulting from the phase change and the motion of the droplet. They provide some insight into the evolution of liquid–vapor phase-exchange processes as well as the solidification evolution of hydrogen particles of various diameters.