Performance of Thermal Energy Storage Unit using Supercooling of D-threitol

Performance of the latent heat thermal energy storage unit which uses supercooling for hot water supply was experimentally investigated. Phase change material (PCM) is D-threitol whose melting point is 87 °C. The PCM is encapsulated in thin and long cylindrical copper capsules. The capacity of each capsule is 912 mℓ. The storage tank is 166 ℓ in capacity and is filled up with 96 PCM capsules. Heat of fusion of the threitol is 28 MJ in total. After the threitol completely melted, part of the sensible heat stored with the threitol is withdrawn, which makes the threitol supercooled. After about eight hours, the threitol is intentionally nucleated to withdraw the remained latent heat and sensible heat stored with the threitol. The result of the experiment shows that the storage unit can control the nucleation of the supercooled threitol. From the result of a cycle of storage operation between 52 °C and 94 °C for one day, 90 % of the initial stored heat in the temperature range was recovered including sensible heat released in the first heat recovery operation.