Comparative study of the thermal performance of four different shell-and-tube heat exchangers used as latent heat thermal energy storage systems

In this paper, the influence of the addition of fins and the use of two different heat transfer fluids (water and a commercial silicone) have been experimentally tested and compared in four latent heat thermal energy storage systems, based on the shell-and-tube heat exchanger concept, using paraffin RT58 as phase change material. Three European institutions were involved under the framework of the MERITS project. A common approach (temperature and power profiles), and five different key performance indicators have been defined and used for the comparison: energy charged, average power, 5-min peak power, peak power to energy ratio, and time. For the same heat transfer fluid, results showed that finned designs (4.7-9.4 times more heat transfer surface) showed an improvement of up to 40%. On the contrary, for the same design, water (which has a specific heat 3 times higher and a thermal conductivity 4.9 times higher than silicone Syltherm 800), yielded results up to 44% higher.