Effect of tube arrays with a low area ratio on the solidification enhancement in shell and tube latent heat thermal energy storage systems

The tube array is an efficient technique to enhance the performance of shell and tube latent heat thermal energy storage systems (LHTESS) and overcome the low thermal conductivity of phase change materials (PCMs). A transient three-dimensional numerical model based on the enthalpy-porosity technique is developed and validated against experimental results published in the literature. A paraffin-based phase change material with a melting temperature of 42–44 °C is used with water as the heat transfer fluid (HTF). The effect of tube arrays on the solidification performance using one, two, three, four, and five inner tubes is investigated with the same PCM mass at a constant flow rate and a fixed ratio of the cross-sectional area of inner tube(s) to shell (0.023), which is the lowest in the literature, i.e., the largest volumetric heat capacity of LHTESS. Then, the eccentricity of the five-tube array inside the shell is examined. The results show that the centered five-tube array reduces the solidification time by 72.0 % and improves the discharge rate and average effectiveness by 138.2 % and 160.7 %, respectively, compared to the single-tube LHTESS. The five-tube array with the best eccentricity reduces the solidification time by 8.86 to 16.15 %, increases the discharge rate by 7.97 to 12.34 %, and improves the average effectiveness by 1.24 to 6.78 %, compared to other tested five-tube arrays. In the daytime, the developed five-tube LHTESS achieves 3.55 complete melting and solidification cycles, while the concentric single-tube LHTESS completes only one.