Numerical simulation on thermal characteristics of supercooled salt hydrate PCM for energy storage: Multiphase model

Multiphase model is set up and applied to perform a 3D transient CFD simulation on the discharging characteristics of supercooled PCM. Three typical processes are identified and analyzed, i.e. stable supercooling, triggering crystallization and regular solidification periods. The simulation is achieved by loading the source term in energy equation and phase transition term in volume fraction equation. PCM temperature, solid fraction (SF) and heat transfer rate (HTR) to the surroundings are monitored and analyzed during the three stages. It is found that there is little difference among the temperature and SF curves of different z-direction planes during the first two periods but they are distinct during the regular solidification period. For the triggering crystallization period, PCM temperature rises much rapidly up to the melting point within 30 s and SF increases up to 0.33 correspondingly. The heat loss is small in this short period and could be simplified as adiabatic. Variations of temperature and SF extend from up and side walls to the interior of the PCM unit. HTR curve fluctuates greatly throughout the three processes with highest value of 1420 W occurring in regular solidification period. The developed method can be used for parameter analysis of supercooled PCM thermal storage devices.