Unipolar Charge Injection Induced Melting Rate Enhancement in a Cylindrical Thermal Energy Storage Unit

Thermal Energy Storage (TES) provides an unique opportunity to balance supply-demand fluctuations in Nuclear Power Plants (NPPs) and Concentrated Solar Power Plants (CSPPs). This study presents a numerical investigation of melting in a Phase Change Material (PCM) based cylindrical shell and tube TES unit enhanced by unipolar charge injection. The governing equations for flow, heat transfer, phase-change and electrostatics are solved using a customized solver developed in the finite-volume framework of OpenFOAM. The solid-liquid melt interface is captured using a fixed-grid approach based on enthalpy-porosity method. Transient behavior of the melting dynamics in the presence of electric field induced unipolar charge injection has been studied. Specific attention has been paid to understand the mechanism of electric field assisted melting process in a cylindrical TES unit. The applied electric potential (V₀) is varied from 0-10 kV and the charge injection strength is considered to be in the medium injection regime (C = 1). The modifications in the flow structure and the interface morphology caused by the electrohydrodynamic (EHD) flow are highlighted. The unicellular flow structure in natural convection dominated melting process transforms into a multicellular flow structure due to the onset of electroconvection. The multiple small flow cells produced by the elec-tric field leads to enhanced mixing and heat transfer. Thus, the melting rate is notably enhanced by the electric field induced unipolar charge injection. A maximum of approximately 87% decrease in charging time is achieved in the parameter space considered, herein.