Effect of unsteady heat source condition on thermal performance for cascaded latent heat storage packed bed

Abstract

The intermittency and fluctuations of heat sources such as solar energy and industrial waste heat have a significant impact on the thermal properties of thermal energy storage systems. The dynamic heat transfer properties of latent heat storage devices under unsteady heat sources need to be further studied to better understand the impacts of thermal fluctuations. In this study, the concentric dispersion model is used to investigate the melting process of a cascaded packed bed phase change heat storage system under sinusoidal fluctuating heat sources. The effects of period and amplitude variations on the thermal performance of the system are investigated, using several metrics for thermodynamic evaluation. The study shows that the effect of low-frequency fluctuation period on the melting of packed bed thermal energy storage (PBTES) is differentiated by the limitation of the total melting time. The thermal performance of the system is enhanced when the fluctuation period is much larger than the melting time, especially the melting time is significantly reduced by 24 % when the period is 120 min, and the opposite is true when the fluctuation period is approximately equal to the melting time. The effect of high-frequency features is smaller. The influence of the fluctuation amplitude on the melting process lasts throughout the process. When the amplitude is 15 °C, the complete melting time is shortened by 23 % compared with the steady condition. At the same time, the increase in the amplitude of the fluctuations enhances the sensitivity of the thermal properties of the system to the variability of the fluctuation period, further amplifying the effect of the period on the enhancement or reduction of the thermal properties of the system. This work provides a certain reference for the design of PBTES under unsteady heat sources.