Conjugated heat and mass transfer during flow melting of a phase change material slurry in pipes

• Conjugated heat and mass transfer of TBAB CHS flowing through the heated pipes were investigated.
• Diffusion of TBAB salt in TBAB aqueous solution was modeled and investigated.
• Interphase heat and mass exchange between the solid and liquid phases was clarified.
• The local heat transfer coefficient was obtained and compared with the experimental result.

PCS (phase change materials slurries) are very useful for thermal energy storage. TBAB (tetra-n-butyl ammonium bromide) CHS (clathrate hydrate slurry) is a promising PCS, which is composed of TBAB hydrate crystal and TBAB aqueous solution. In the present study, the flow melting characteristics of TBAB CHS through pipes were numerically investigated. The solid–liquid two-phase nature of TBAB CHS was numerically investigated using the Eulerian–Eulerian multiphase model. And the interphase heat and mass exchange between TBAB hydrate crystals and TBAB aqueous solution was numerically modeled by considering the phase change phenomenon. Moreover, the diffusion of TBAB salt (solute) in TBAB aqueous solution was also numerically investigated. The numerical results showed that the liquid temperature increased more quickly than the solid temperature because of the latent heat involved. Moreover, the local heat transfer coefficient decreased in the thermally fully-developed region because of the increasing temperature difference between the wall and fluid. When the solid particles were almost fully melted, the fluid temperature increased more quickly than the wall temperature due to the absence of phase change, resulting in the increase of the local heat transfer coefficient.