Lattice Boltzmann simulation of forced convection melting of a composite phase change material with heat dissipation through an open-ended channel

Abstract

This paper performs a numerical analysis of time-dependent forced convection heat transfer in an open-ended straight channel filled with a metal structure and paraffin as a phase change material (PCM). The unsteady two-dimensional governing equations, based on the Darcy-Brinkmann-Forchheimer (DBF) model and the two-energy transport equations (i.e. local thermal non-equilibrium, LTNE) at the representative elementary volume (REV) scale in their dimensionless forms, have been simulated using the thermal single relaxation time (T-SRT) Lattice Boltzmann Method (LBM) with three distribution functions to handle the fluid, and temperatures of the fluid and solid phases. Effects of Reynolds number (100 ≤ Re ≤ 600), Eckert number (0 ≤ Ec ≤ 10), porosity (0.1 ≤ ɛ ≤ 0.8) on dynamic and thermal fields, entropy generation, and energy and exergy efficiencies of the considered system are examined. The relevance of these parameters is highlighted and discussed during the charging (melting) and discharging (solidifying) processes. Interestingly, it can be stated that small porosities promptly accelerate these two processes due to high thermal conductivity of the metal foam/PCM composite, and improve energy and exergy efficiencies of the system, whatever Re for the very low porosity values (0.4 and 0.6). In addition, streamlines, isotherms and melt front (phase field) are exhibited for this parameters range. Based on the findings obtained, it is concluded that, in the context of laminar forced convection melting of a composite PCM with heat dissipation in a porous PCM-filled channel, 1) there is a critical Reynolds number for which the storage energy is optimal and whose quality is improved using both the porosity and the effects of viscous dissipation, and 2) the proposed approach's potential and the in-house code flexibility implemented are demonstrated.