A comprehensive study on melting enhancement by changing tube arrangement in a multi-tube latent heat thermal energy storage system

In this study, the paraffin wax's melting dynamics in a multi-tube latent heat thermal energy storage system are investigated. The performance of ten arrangements of five heat transfer fluid tubes is compared. The radial eccentricity of four planetary tubes is varied around a fixed central tube. The study aims to find an appropriate arrangement of multiple HTF tubes keeping the same PCM content and heating surface. A simplified two-dimensional computational domain was considered, an enthalpy-porosity based melting model was designed, and the governing equations were solved using ANSYS-Fluent. The melting sequence in various cases is repre-sented as the liquid fraction contours, flow streamlines, and temperature contours. The performance of proposed designs is assessed on the basis of transient plots of liquid fraction, average domain velocity, and heat flux at the outer surface of the heat transfer fluid tube. It is observed that the melting dynamics are greatly influenced by the tube arrangement. The coalescence of small vortices and the intermixing of different temperature layers accel-erate the melting. It is found that the tubes in the top half should be placed closer to the center to delay thermal stratification, and in the bottom half should be placed deeper into the poor melting zone. The staggered arrangement of planetary tubes outperforms the inline arrangement at given eccentricities. The fastest and slowest melting is realized by Case 9 and Case 1, which take 128 and 269 min, respectively, for melting. The proposed designs can store 1450 kJ/m of energy with 98 % theoretical efficiency.