Thermal performance analysis and optimization of a double-layer spherical phase-change material capsule with annular fins

摘要

Spherical phase-change material (PCM) heat storage units are widely used in packed-bed heat storage systems in different temperature regions. To enhance the thermal response of spherical PCM capsules, we proposed a double-spherical PCM capsule structure with annular fins. An experimental system was established to monitor the temperature variation of the spherical PCM melting process and the accuracy of numerical simulation was verified. The effects of fin parameters on the thermal and melting properties of double-spherical PCM capsules were analyzed by numerical simulation. The results showed that the best fin installation position was outside the inner ball. The heat storage time of the capsule was inversely proportional to the number of fins and could be shortened by 14.4 . However, the entropy production increased linearly with an increase in fin parameters. The addition of fins changed the law of natural convection in the capsule, and it was easier to form local natural convection in small areas, and the Nusselt number (Nu) was proportional to each fin parameter. The single-factor optimization results showed that the optimal combination of fin parameters was Num = 3, H/L = 80 , and D = 0.5 mm for a spherical capsule with outer and inner sphere diameters of 50 and 30 mm, respectively. Thus, the proposed heat storage unit structure would further improve the thermal response rate and ensure safe and stable operation of the PCM heat storage device.