Employing spiral fins to improve the thermal performance of phase-change materials in shell-tube latent heat storage units

Adding metal fins to extend the heat transfer area is a viable and effective technology to improve the poor thermal conductivity of Phase-Change Material (PCM). The annular fin is the most common type due to the simple structure, but it weakens the natural convection. Under this condition, the spiral fin is proposed to overcome the poor natural convection. An experimental system was built with three vertical shell-tube latent heat storage units (LHSU), two of which employed annular and spiral fins with the same heat transfer area by taking one without fin as a reference. The melting and solidifying status, temperature distribution and comprehensive efficiency are used to evaluate thermal performance of three LHSUs. Experimental results show adding metal fins contributes to the heat transfer improvement, especially for spiral fins. Employing metal fins can weaken PCM natural convection, but annular fins have a lower weakening efficiency than spiral fins on PCM natural convection. Therefore, the spiral fins provide superior thermal performance with enhanced multi-circulation flows. Compared with annular fins, employing spiral fins can increase the average Nusselt number by 28.6%, the average heat transfer rate by 20.9%-58.2% in charging and discharging processes, and the average heat flux by 17.5%-53.8% in LHSUs.