Apparent heat capacity method to describe the thermal performances of a latent thermal storage system during discharge period

Abstract

In this work, a novel detailed dynamic model for latent cold thermal storage unit containing water as phase change material (PCM) is presented. The proposed dynamic model is based on transient energy balances for both PCM capsules and heat transfer fluid (HTF). The apparent heat capacity approach is used to model phase transition processes in PCM, where the PCM heat capacity is given as a temperature-dependent function. This method can be simply integrated into a variety of software to assess the energy efficiency of latent storage. The dynamic model of the PCM storage unit is validated using measured results from the literature and it is used to investigate the influence of multiple parameters on the storage thermal performance. The obtained result show that the PCM melting process varies in both axial direction and radial direction in the storage unit. It was also observed that the higher the height of the tank, the longer the discharge period. Increasing the diameter of capsules from 47 mm to 77 mm leads to increase the discharging period by about 30%. In addition, varying the storage tank initial temperature between −8 °C and −4 °C does not have a significant effect of on the discharging time. Finally, it was recommended that for improving the storage performance and minimizing water pumper energy consumption, a compromise between the HTF flow rate and the capsule diameter must be determined.