Numerical study of melting process of a high-temperature phase change material including natural convection and turbulence

Abstract

The design and optimisation of a latent heat thermal storage system require knowledge of flow, heat and mass transfer during the melting (charging) and solidification (discharging) processes of hightemperature phase change materials (PCMs). Using fluent, numerical modeling was performed to study the impact of natural convection and turbulence in the melting process of a high-temperature PCM in a latent heat storage system with Ra = 10 12. Numerical calculation was conducted, considering a two dimensional symmetric grid of a dual-tube element in a parallel flow shell and tube configuration where the heat transfer fluid passes through the tube and PCM fills the shell. Three melting processes of PCM were considered; pure conduction, conduction and natural convection, and finally the latter with turbulence. The first study showed a one dimensional melt front, evolving parallel to the tube, which results in lower peak temperatures and temperature gradients, higher heat transfer area for a longer period of time, however lower heat transfer rate due to natural convection being ignored. The second study presented a two dimensional melt front which evolves mainly perpendicular to the tube, shrinking downward, resulting in the loss of heat transfer area and higher peak temperatures and temperature gradient, however, the higher rate of heat transfer rate due to the creation of convection cells which facilitate mass and heat transfer. Including turbulence led to a higher mixing effect due to the higher velocity of convection cells, resulting in a more uniform process with lower peak temperature and temperature gradients and higher heat transfer rate. In a melting process with Ra>10 11 , including convection and turbulence impact provides more realistic data of flow, mass and heat transfer.

Numerical Analysis on Hot Water Storage Tank Integrated With Phase Change Materials

“…Several numerical studies were conducted to investigate the effect of three different melting processes of high temperature PCM including pure conduction, conduction and natural convection. According to the results, including the turbulence flow led to a higher mixing effect which resulted in a more uniform process with a lower peak temperature and higher heat transfer rate [14]. Studies do not often consider the application of metallic PCMs due to the high weight and cost related to these materials.…”