Semi-analytical thermal modeling of transverse and longitudinal fins in a cylindrical phase change energy storage system

Abstract

Inclusion of fins in phase change energy storage systems has been widely investigated for improving the rate of energy storage. Despite significant past experimental research in this direction, there is a lack of comprehensive theoretical models for fin-based enhancement in energy storage, particularly for cylindrical geometries. This is a considerably challenging, non-linear problem. This paper presents a semi-analytical model for temperature distribution and energy storage in an annular phase change material (PCM) material around a hot cylinder in the presence of transverse and longitudinal fins extending into the PCM. Two distinct pathways for heat transfer into the PCM are analyzed separately and expressions for total heat flux into the PCM are determined for both fin types. The perturbation method is used for analyzing the non-linear phase change problem and determining the heat flux into the PCM through the fin. The dependence of total energy stored on fin thermal properties and geometrical parameters is determined. Results indicate key similarities and differences between cylindrical fins and recently-reported Cartesian fins. It is shown that even a thin fin results in considerable heat transfer enhancement. Results also indicate diminishing results when the fin size is further increased. Theoretical modeling presented in this paper improves the fundamental understanding of an important heat transfer enhancement strategy for phase change based energy storage systems. Results discussed here may help improve the practical design of finned, cylindrical phase change energy storage systems that are commonly used for harnessing renewable energy.