Unsteady temperature, heat transfer rate and HTF outlet temperature variation during charging of latent thermal energy storage unit

Abstract

This work reports a detailed numerical study that is aimed to determine the variation of the three principal parameters, temperature of two phase change materials (PCMs), heat transfer rate and heat transfer fluid (HTF) outlet temperature, during charging of latent thermal energy storage unit (LTES). The unit is consisting of a shell-and-tube type. The shell space is filled with two paraffin wax named PCM1 and PCM2. During charging process, hot fluid heats the PCMs, and when PCMs melts, the heat is stored. A mathematical model based on the conservation energy equations was developed and numerically investigated. Numerical results show that, the variation of the three principal parameters goes through three distinct periods. As time progress, the heat transfer rate increases, reaches its maximum value during the first period, and then decreases, until finally it equals zero. The HTF outlet temperature remains constant and is equal to its initial temperature for approximately 200 seconds. During this time period, the heat storage capacity is greater, PCM1 and PCM2 store energy in the sensible form only. The analysis and discussion of results are employed to evaluate the correspondence between the variations of the three parameters in term of charging time.