要約

This paper presents a numerical study based on the energy equations for the transient thermal behavior of a concentric double pipe latent thermal energy storage (LTES) unit for solar water heating applications. The annular space between tubes is filled with two paraffin wax phase change materials (PCMs), named PCM1 and PCM2. A heat transfer fluid (HTF: saturated water) flows through the inner tube and transfers the heat to the PCMs. Several numerical investigations were conducted in order to examine the effects of the HTF inlet temperatures on the variation of the temperature of PCM1 and PCM2, melting fraction, melting and solidification time, HTF outlet temperature, heat transfer rate, and total energy stored. Numerical results show that charging and discharging processes have three distinct periods for the change of PCMtemperature and melting fraction.When the temperature difference between the HTF inlet temperature and PCM increase, the variation of the temperature and melting fraction in different locations in the PCM increases considerably, and then the charging and discharging process is rapidly reached. The melting times of PCM1 and PCM2 decrease with an increase in the HTF inlet temperature. Moreover, the decreasing degree of their melting times is different. The present analysis provides theoretical guidance for designing optimization of a concentric double pipe LTES unit filled with two PCMs.