Role of PCM addition on stratification behaviour in a thermal storage tank - An experimental study

The present paper aims to analyse the effect of addition of phase change materials (PCM) encapsulated in spherical capsules at the top of a hot water storage tank for stratification enhancements during the charging process. The experiments were performed in a cylindrical storage tank of capacity 115 L at various flow rates and inlet temperatures of heat transfer fluid (HTF). The temperature profile along the height of the storage tank was analysed for both the thermal energy storage (TES) systems with and without the addition of PCM capsules. The experimental results showed that the overall charging time required was lesser in the sensible thermal energy storage system compared to the system with PCM capsules. However, this difference in charging time was reduced with increase in HTF inlet temperature. The stratification behaviour was analysed using the various non-dimensional numbers such as stratification number, Richardson number, charging efficiency and Cumulative charge fraction for both the TES systems. Better stratification was attained in sensible TES system at lower HTF inlet temperature for all flow rates considered. However, the effect of addition of PCM capsules increased the stratification capability as the temperature difference between the inlet HTF and PCM melting temperature was increased. (C) 2016 Elsevier Ltd. All rights reserved.