A coupled lattice Boltzmann-finite volume method for phase change material analysis

The aim of this work is to present results obtained through a multi-physics solver used to numerically determine the thermal behaviour of a phase change material both for solidification and melting processes. Particular attention is addressed to the right implementation of PCM properties, which are not constant with respect to the considered phase. Thus, the energy equation is specifically rewritten for the PCM material in terms of enthalpy, in order to consider both sensible and latent heat. Liquid and solid enthalpy thresholds are fixed with respect to solid/liquid properties, to correctly determine the amount of PCM which undergoes the phase change. The implemented model allows varying the temperature (enthalpy) range where the phase change takes place. The influence of mushy area thickness (the intermediate zone between solid and liquid) has analysed both for charging and discharging processes in a heat exchanger-like geometry. Additionally, the LB equation itself is rewritten in order to deal with the solidification/melting front advance. Results show how the under-analysis phenomena are sensitive to solidification/melting front thickness, with predominant effects whenever conduction is the thermal driver. Effects are definitely tamed while convection plays a role. Results also show how, for the implemented heat exchanger operating conditions, the considered PCM (PureTemp37) can be completely melted in 5 h, independently from the mushy zone thickness (Delta T = [0.01,1.00,3.00]K). On the contrary, for the same duration of the discharging process, the solidified fraction ranges from 23% up to 35% whereas the mushy zone Delta T ranges from 0.01 K up to 3.00 K.Numerical results are compared with a set of literature/analytical data available for a range of non-dimensional numbers and both for conduction and convection driven phenomena. The agreement between numerical and literature data is satisfactory with positive outcomes for future model developments.