Experimental analyses of solidification phenomena in an ice-based thermal energy storage system

Abstract

Latent thermal energy storage devices can efficiently store surplus thermal energy during off-peak hours. The system's phase change material (PCM) improves energy storage capacity and isothermal properties. Most PCMs have weak thermal conductivity, which hampers heat transfer. Thus, the present analysis involves an insight into the heat transfer characteristics and thermal performance of a vertical tube-in-tank cold storage system. The objective of this investigation is to gain a better understanding of the significance of buoyancy-driven convection within the side bulk region during the discharging of water as PCM in the heat exchanger. A series of experiments are conducted to investigate the effect of varying the initial bulk temperature on the rate of PCM solidification. The effects of three distinct initial bulk temperatures which are 20 °C, 15 °C, and 5 °C on the solidified mass fraction, thermal performance, and heat transfer rate at various radial and axial locations in PCM are examined. It is seen that PCM experienced a varying cooling rate with varying axial height and is found to be the highest in the bottom region. PCM temperature decreases from top to bottom under the cases of 20 °C and 15 °C, respectively. In contrast, a narrow-ranged thermocline layer is observed under 5 °C bulk temperature, making uniform temperature distribution within the bulk. The influence of bulk natural convection prevails in the later stages of the discharging process under 5 °C bulk, whereas it predominantly exists during the initial stages of solidification under bulk temperatures of 20 °C and 15 °C.