Effects of shell modifications and operational parameters on melting uniformity of a vertical multi-section shell-and-tube latent heat thermal energy storage unit

In this study, a vertical shell-and-tube LHTES unit model is developed, which combines the techniques of annular fins, multi-PCM structure and shell modifications. The effects of shell modifications (including the variations of material and shell angle, alpha) on melting uniformity are numerically investigated based on a two-dimensional model with three PCM sections and the same total PCM volume. The influence of shell and fins materials on melting performance is initially discussed. Different melting fronts can be observed by changing materials and the bottom shell is found to be the critical location for enhancement. Then, Ste* and Re are adopted to scrutinize the combined effect of operational parameters. The results show that Ste* should be given priority to reducing melting time rather than Re. Besides, the melting uniformity of PCM is explored by varying alpha from 0 degrees to 3.5 degrees. The results indicate that adopting the critical angle (alpha*) can effectively improve the melting uniformity of different sections as well as shorten the total melting time. Furthermore, it is found that inlet temperature of HTF hardly affect the value of alpha*. In conclusion, these findings provide a guideline to the design and operation of multi-section LHTES unit.