One of the most applicable geometries for a thermal energy storage unit is an annulus filled by phase change material (PCM). In time-sensitive applications, the charging and discharging rates of PCM are critical. In the early stage of the period, the phase change rate is high, and it becomes so low by progressing the time, especially in the pure conduction zone at the later stage. Staggering the tube increases the charging or discharging rates and decreases another. The enhancement of both the charging and discharging rates is desirable. To achieve this in the present study, to improve the heat transfer and phase change rates, the application of the magnetic field of an electric current-carrying wire at the top or the bottom of the annulus in order to induce a convection heat transfer in the nanoparticles-enhanced PCM (NePCM) is presented. The solution is validated with experimental and numerical data. The predicted result indicates that employing the wire at the top of the annulus can reduce the solidification time by 25%. The application of the magnetic field is more efficient in the charging process where the wire is employed under the annulus, which intensifies the melting rate up to 40%. Accordingly, considering the appropriate locations of the wire, a conceptual design of thermal energy storage unit under the magnetic field efficient in both charging and discharging processes is developed.
