Thermal performance of a novel dual-PCM latent thermal energy storage unit with an inner spiral coil tube

A novel dual-PCM latent thermal energy storage (LTES) unit with an inner spiral coil tube is proposed for improving thermal performance. A detailed numerical investigation is presented for the thermal performance of the charging process. The novel dual-PCM LTES unit has more charging capacity than the traditional single PCM LTES unit, it can provide a more uniform temperature distribution and thus lead to a fast charging process. The dual-PCM unit with the optimal structure of the volume ratio 1:1 and the phase change temperature difference of 30 K between the two PCMs can increase the average heat transfer rate by up to 62 %, compared with the single PCM unit. The effects of the Stefan number on the thermal performance are significant because the charging time decreases by 56 % as an increase of the Stefan numbers from 0.17 to 0.53. As the value of the Reynold number increases from 500 to 1000, the average heat transfer rate increases by 31.6 %, whereas the effects of the Reynold number on the thermal energy storage capacity can be negligible for Re >= 1500. Those operating and structure parametric studies offer guidelines for improving the thermal performance and optimizing the design of the dualPCM spiral coil LTES unit.