A hybrid method for modeling the unconstrained melting of phase change material in hot water tanks

Abstract

In this study, a novel hybrid method for modeling the unconstrained melting of phase change material (PCM) in hot water tanks was proposed. This method analytically calculates solid PCM settling velocities and prescribes them by Darcy terms of numerical models. Its main advantage is that the settling of solid PCM during melting processes is considered without reconstructing solid PCM surfaces and coupling the force balance equation. Analytical algorithms of settling velocities were deduced for PCM encapsulated in rectangular, spherical and cylindrical enclosures. Based on these algorithms, corresponding unconstrained melting models were developed and validated by the experimental results of previous studies. The results show that the developed model achieved satisfactory performance. In particular, no unphysical deformation occurred during the melting process, and the predicted melt fronts had a good agreement with that of the experiment. Moreover, the mean absolute error in liquid fractions between the experimental and numerical results was 4.05%, 6.31% and 4.04% for PCM encapsulated in the rectangular, spherical and cylindrical enclosure, respectively. A further analysis of the solid PCM settling velocity indicates that no oscillation occurred in the simulation results of this study, and thus the model stability was also improved by using the proposed method.