A REV-scale assessment of metal foam porosity effect on a PCM’s melting in an latent heat energy storage unit
Latent heat thermal energy storage (LHTES) has become both a promising and attractive thermal energy storage (TES) method that can achieve high energy storage density and near constant temperature during operation while balancing the gap between energy supply and demand.
This paper deals with the numerical investigation of the enhancement of heat transfer under forced convection in an open-ended horizontal channel filled with a porous structure (metal foam) and a phase change material (PCM: paraffin). The Forchheimer-Brinkman extended Darcy unsteady flow model (generalized Navier-Stokes equations) is assumed to simulate flow and heat transfer occurring within the porous medium for an unsteady forced convection. These are completed by two energy equations based on the local thermal non-equilibrium (LTNE) condition.
Simulations are done using the thermal Single Relaxation Time (T-SRT) lattice Boltzmann Method (LBM) at the representative elementary volume (REV) scale. All lattice Boltzmann equations (LBE) involved are discretized according to the D2Q9 model using three distribution functions. Numerical results were performed to present the effects of porosities (0.5-0.9) on the dynamic and thermal fields, Bejan number and melting front for the sequent Re range (200-400) during charging (melting) process.
The reliability of the implemented in-house code has been evinced through a comparison of some preliminary results with some results from the literature. Based on the results achieved, it can be stated that the melting process under laminar forced convection is speeded up by decreasing the porosity (=0.5) and increasing the Reynolds number. In addition, high porosity (=0.9) decelerates the front progression owing to the permeability of the metal structure. While, increasing the porosity intensifies the thermal conductivity of the medium and then, induces more energy stored in a short time within the same volume of the support. Thereby, at high Re (=400), it can be stated that the melting phenomenon rate is much faster owing the interstitial heat transfer. However, the heat transfer irreversibility dominates the overall irreversibility of the system.
Finally, it can be concluded that the implemented thermal lattice Boltzmann method represents an appropriate tool that can handle unsteady forced convection melting problems in latent energy storage unit.