Comparison of heat transfer between cylindrical and conical vertical shell-and-tube latent heat thermal energy storage systems

The shell-and-tube latent heat thermal energy storage (LHTES) system has been widely studied. In this paper, the effect of geometric design on vertical shell and tube LHTES systems is investigated. Accordingly, cylindrical and conically shaped experimental tests are developed for this purpose. The thermal performance of the conical and cylindrical systems is compared experimentally and theoretically. The temporal variation of the experimental temperature is used to validate the mathematical model and demonstrate the effects of natural convection on heat transfer in the phase change material (PCM) during the charging and discharging processes of both systems. The melting/solidification time, liquid fraction, and stored/released energy are used to evaluate the performance of the two systems. The results show that the conical system can store thermal energy much faster than the cylindrical system at the same operating condition at a specific charging time before the system is fully charged. This is enabled since the conical design allows natural convection to dominate in a large volume of PCM at top of the container. However, there is no significant difference during the discharging process. The results indicate that the natural convection effect can be advantageously utilized by optimization of the design of the shell-and-tube LHTES system.