Heat storage performance analysis and parameter design for encapsulated phase change materials

This paper establishes a thermo-mechanical model considering the liquid density variation to explore the comprehensive energy storage performance of two types of small-sized encapsulated phase change materials (PCMs) as well as effects of shell thickness. The study shows that the varying ranges of internal pressure, melting temperature and latent heat are markedly diminished during melting of PCMs after taking into account the liquid density variation. The decrease of shell thickness leads to a decrease of maximum internal pressure and a larger decrease of critical cracking pressure, which will increase the risk of shell cracking. The decrease in shell thickness slows down the increase in melting temperature and the decrease in latent heat during the melting process, which consequently reduces the melting time and increases the stored latent energy. These results indicate that reducing shell thickness of encapsulated PCMs is favourable for elevating energy charging rate and energy storage capacity while it is harmful to mechanical stability. The Cu/Ni capsule has smaller critical core/shell size ratio to avoid cracking than the salts/SiC capsule, while the former offers a shorter melting period. This implies that physical properties of materials of PCM capsules should be carefully considered for improving mechanical stability and melting dynamics. This study is helpful for selection of appropriate shell thickness and materials to achieve excellent comprehensive energy storage performance of encapsulated PCMs.