Evaluation and optimization of melting performance in a horizontal thermal energy storage unit with non-uniform fins

Abstract

The shell and tube latent heat thermal storage systems are widely used in the storage and utilization of fluctuating thermal energy resources due to high thermal storage density, constant discharge temperature, simple processing and low cost. Adding fins to phase change materials is an effective method to expand the heat transfer area and improve the heat transfer rate. However, the obvious thermal stratification phenomenon and slow melting rate problem are exited in the horizontal latent heat thermal energy storage system. In order to improve the melting rate and uniformity, different non-uniform fin arrangements were designed and investigated in this study to improve the thermal performance. A numerical model of the melting characteristics of phase change materials was established and validated by the experimental results in the literature. The effects of fin arrangement, angle and length on the thermal performance of the melting process were quantitatively evaluated by analyzing the temperature field, velocity field and liquid fraction distribution before and after melting. Results indicated that when the fin angle α=25° and the fin length L=40 mm, the melting time is decreased by 83.9% and thermal storage density is improved by 466%, which meant that the lower fin arrangement realized the synergistic enhancement of natural convection and heat conduction. On this basis, the effect of the heat transfer fluid temperature on the thermal storage performance of the optimal scheme was further studied. The non-uniform fins design proposed in this study can provide theoretical support for the design method of thermal storage system, and contribute to the efficient utilization of intermittent thermal energy resources such as solar energy and industrial waste heat.