| Cascaded latent heat thermal energy storage(LHTES)technology is widely investigated as an efficient and flexible thermal energy storage technology.In this paper,a two-dimensional axisymmetric physical model of three-stages cascaded LHTES unit is developed.The shell side of each heat exchanger are filled with three kinds of phase change materials(PCMs),respectively.the PCMs accounts for 85%of the container capacity,and the PCMs are arranged in order of the melting temperature.Firstly,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.Secondly,the application of finned heat transfer enhancement technique in cascaded LHTES unit is discussed.Meanwhile,the effects of fin quantity and height,and the different strengthening effects of even and uneven fins distribution on three-stages PCMs are compared and analyzed.Thirdly,the setup of the cascaded LHTES system of medium-high temperature is introduced in detail.The results show that the PCM with lower melting temperature leads to faster charging rate and releases more heat in the cascaded LHTES system.Comparing with the non-cascaded LHTES system,proper selection of the PCMS can make the cascaded LHTES system more flexible.Comparing to even number layout,the system with uneven number layout can shorten the total time of the melting and solidification processes by 5.2%and increase the average discharging power by 12.6%,so the cascaded LHTES system can enhance heat transfer efficiency at the cost of fewer fins.Besides,comparing to even height layout,the system with uneven height layout can slightly decrease the total time of the melting and solidification processes but hardly affect the average charging and discharging rate.The findings can guide the design and heat transfer enhancement to the cascaded LHTES system with fins. |
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