Among the different types of phase change materials, paraffin is known to be the most widely used type due to its advantages. However, paraffin’s low thermal conductivity, its limited operating temperature range, and leakage and stabilization problems are the main barriers to its use in applications. In this research, a thermal energy storage unit (TESU) was designed using a cylindrical macroencapsulation technique to minimize these problems. Experimental and numerical analyses of the storage unit using a tubular heat exchanger were carried out. The Ansys 18.2-Fluent software was used for the numerical analysis. Two types of paraffins with different thermophysical properties were used in the TESU, including both encapsulated and non-encapsulated forms, and their thermal energy storage performances were compared. The influence of the heat transfer fluid (HTF) inlet conditions on the charging performance (melting) was investigated. The findings demonstrated that the heat transfer rate is highly influenced by the HTF intake temperature. When the effect of paraffin encapsulation on heat transfer was examined, a significant decrease in the total melting time was observed as the heat transfer surface and thermal conductivity increased. Therefore, the energy stored simultaneously increased by 60.5% with the encapsulation of paraffin-1 (melting temperature range of 52.9–60.4 °C) and by 50.7% with the encapsulation of paraffin-2 (melting temperature range of 32.2–46.1 °C), thus increasing the charging rate.

One of the most effective methods of thermal energy storage is the use of Phase Change Materials (PCM). Paraffin, which is among the organic PCMs, is frequently used in thermal storage applications due to its easy accessibility and high heat storage capacity. However, it significantly limits the thermal charge / discharge (melting / solidification) rate of systems caused by their low thermal conductivity. There are many methods applied to enhance the thermal conductivity of paraffin. In this research, the melting processes of pure paraffin (Rubitherm RT50) and paraffin containing 10% Al2O3 nanoparticle in a rectangular melting area were numerically investigated. For comparison, the effect of increasing the wall temperature of the rectangular area to 65 ° C, 70 ° C and 75 ° C on the total melting time was investigated for both pure paraffin (melting temperature 50 ° C) and paraffin with nanoparticle additives. In this study, in which the Computational Fluid Dynamics (CFD) approach was used, ANSYS Fluent software was used to perform numerical analysis. Consequently it was determined that the use of Al2O3 nanoparticles improved the rate of paraffin heat transfer.