A transient, two-dimension model is developed to investigate the charging and discharging processes of a three-stages cascaded latent heat thermal energy storage unit. Each phase change material is incompletely filled in the shell side of a vertical shell-and-tube heat exchanger. The liquid fractions, temperatures, and accumulated thermal energy of the PCMs during the fully charging and discharging processes, as well as the effects of the HTF inlet temperature, are analyzed. The results show that lower melting temperature of the PCM causes faster charging rate and more released heat in the cascaded LHTES system. Compared with the non-cascaded LHTES systems, the cascaded LHTES systems can possess better flexibility via the selection of the PCMs.
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