Numerical analysis of melting time and melt fraction for bottom charged tube in tube phase change material heat exchanger

Multiple factors govern the thermo-hydraulic behaviour of latent heat storage devices. The correlation among these factors varies from case to case. In this work, a concentric tube in tube latent heat storage system is numerically modelled. A fixed grid enthalpy porosity approach is adopted to account for phase change. The grid independence is achieved by testing mesh size, time step, and maximum iterations per time step. The computational approach is validated against the experimental data. It has been found that at the higher Rayleigh numbers, the bottom charging will result in faster melting compared to top charging. So, bottom charging is analysed in this work. Non-dimensional parameters, viz Rayleigh number (3.04x10 5 to 65.75 x10 5 ), Stefan number (0.2 to 1), Reynolds number (600 to 3000), and L/D ratio (2 to 15), are varied in the respective ranges mentioned in parenthesis. Stefan number is found to have a major influence on the Melt Fraction and Melting time , compared to Rayleigh number and Reynolds number . Correlations are developed for quantifying the melt fraction as MF = C.St A .Ra B .Re C .Fo D .(L/D) -F . Also, for the dimensionless melting time , correlation is proposed in the form Fo cm = G.(L/D) H .St -J .Ra -K .Re -L .