Thermal energy storage offers the unique ability to decouple, in time, the production of a thermal energy stream from its utilization. However, the analysis and optimization of storage-based energy systems hinges upon the availability of models capable of faithfully representing the salient characteristics of the thermal storage device. In this paper, results are presented for a composite-medium model for the vertical temperature profiles observed in stratified, liquid-sensible thermal storage devices. By varying the magnitude and time-dependency of the diffusivities in the composite medium, the approximate analytical solutions exhibit the growth rates and asymmetry observed empirically. The solutions are described by only two parameters in addition to those of the uniform diffusivity case. The simplified model therefore provides a succinct model capable of reproducing key characteristics of stratified thermal storage behavior.
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