Numerical study of melting and solidification in a wavy double-pipe latent heat thermal energy storage system

The objective of this paper is to develop the influences of channel waviness on the performance of a latent heat storage system during phase change mechanism. The heat exchanger is a vertically oriented double pipe where the heat transfers to/from the PCM in the annulus by moving the water in the inner tube. Various wavelengths, as well as wave amplitudes, are examined at various fluid Re and water temperatures (T-in) to find the effects of channel waviness on different aspects of melting/solidification time, pressure drop, pumping power and exchanged heat rate. Increasing Re, T-in and amplitude of wavy wall improves the system performance during melting and solidification mechanisms. Besides, it is found that there is an optimum dimensionless wavelength of 0.2 for achieving the minimum melting and solidification times as a result of maximum heat exchanged between the water and PCM. Furthermore, the waviness has an almost negligible effect on the pumping power which is reduced for the dimensionless wavelengths higher than 2.0. In the best scenario, the required time to melt and solidify the PCM reduces by almost 28.6% and 57.63%, respectively, using wavy channels compared with the smooth wall case.