Melting behavior of an organic phase change material in a square thermal energy storage capsule with an array of wire electrodes

Abstract

A numerical analysis of melting of an organic phase change material (PCM) in a square thermal energy storage (TES) capsule with an array of high voltage wire electrodes has been performed. Fully coupled set of governing equations for fluid flow, heat transfer, phase change, electric field and charge transport are solved using the opensource finite-volume framework of OpenFOAM. The melt interface is tracked using a fixed grid approach based on enthalpy-porosity method. The main objective of the study is to investigate the effect of direction of electric field on the melting process under different configurations of grounded walls. The transient evolution of the melting process in the presence of electric field is mapped in terms of liquid fraction, mean velocity and mean Coulomb force. The melt flow morphology, temperature field, velocity and electric field distribution at different grounded electrode configurations are visualized. Electric field leads to generation and coalescence of small vortices that influence the melt interface, velocity distribution and the total melting performance. 12 cases with different grounded wall configurations that lead to different electric field directions are considered, herein. Grounding the left and right walls of the square TES capsule notably influence the melting performance. Case 4 with grounded left wall led to the shortest melting time of 2.68 h with 97 % reduction, as compared to the case without electric field (5.28 h). Case 5 with grounded right wall has a negative impact on the total melting time (5.55 h), which is 4.86 % higher than the case without electric field (5.28 h). In general, application of electric field led to an increase in total achievable melt fraction for a given period of 6 h. Case 2 with all the four walls grounded led to a maximum melt fraction of 0.97 which is 9.39 % higher than the case without electric field (0.88). Case 4 with grounded left wall showed the maximum power storage capacity of 17.2 kW which is 49.3 % higher than the case without electric field (8.7 kW). Results presented in this study provide deeper insights on the mechanisms of electric field on melting process and will serve as a reference for design of a TES module assisted with electrohydrodynamic (EHD) flow induced by an array of wire electrodes.