Numerical Study on Melting Phase Change under Microgravity.

A theoretical model of unsteady melting heat transfer in a horizontal tube-shell TES unit is established and numerically solved based on the enthalpy-porosity method. In present research, the evolution of temperature field, velocity field, melting front and PCM enthalpy during the melting process under gravity and microgravity fields are compared and analyzed. The results indicate that the melting heat transfer under microgravity is dominated by heat conduction, while the natural convection dominates in the melting process under gravity. Consequently, melting performance under microgravity is weaker than that under gravity. Under gravity condition, vortices appear in the top half of the PCM and accelerate the melting process, and then the melting rate slows down gradually with the decrease of temperature gradient in PCM. However, due to no flow in the melting zone and the poor thermal conduction of PCM under microgravity, the melting area moves slowly outward in a circular type along the radial direction. In addition, the enthalpy difference of PCM under these two cases gradually enlarges as the melting goes on. At a typical time of 26,000 s, the enthalpy value of PCM under gravity is twice that under microgravity. [ABSTRACT FROM AUTHOR]