Biomimetic phase change capsules with conch shell structures for improving thermal energy storage efficiency

Abstract

Latent heat storage system utilizing a packed-bed setup with encapsulated phase change materials (EPCMs) can address the issues of mismatched energy supply and demand, in addition to preventing the leakage concerns associated with unencapsulated PCMs, which has a broad application prospect. Drawing on the principles of biomimicry, this work proposes bionic-conch and bionic-mitochondrial encapsulation models for PCMs and analyzes the heat transfer performance with different structures. Significantly, the thermal energy storage efficiency of the bionic-conch structure surpassed that of the bionic-mitochondrial and straight-fin structures by 43.11 % and 14.62 %, respectively. The enhanced thermal energy storage efficiency of the bionic-conch is attributed to the spiral fins within, which considerably amplify the heat exchange surface area. Furthermore, in order to obtain the bionic-conch capsule structure with optimal thermal properties, the present work investigates the influence of fins on the melting characteristics of PCMs. The results show that increasing fins empower the thermal energy storage efficiency by 402.89 % and thermal response rate by 616.93 %, respectively. However, there is an issue of slow melting process in the annular region and incorporating an array of a slightly off-center heat-conducting ring (SOHR) is considered to enhance localized heat transfer. The suggest that it can alleviate the problem of slow heat transfer rate in the local annular region and increase the average internal temperature. Furthermore, in order to compensate for the loss of thermal energy capacity of the fin structure, this work also investigated the effect of different wall thicknesses on the thermal performance of the phase change capsule. Interestingly, decreasing the wall thickness significantly increases the heat capacity. In concrete terms, the thermal energy capacity of 0.5 mm wall thickness is increased by 22.87 % compared to 2 mm. This study may provide new enlightenment for the optimization of green energy.