Saeed Ranjbar - M.Sc. graduate, Shahid Beheshti University
Ramin Haghighi Khoshkhoo - Associate Professor, Shahid Beheshti University

Nowadays, latent heat storage materials are being widely used in different industries, especially renewable energy systems. Their low thermal conductivity, however, is a limiting factor in their utilization in large scales. Numerous methods have been presented for heat transfer enhancement in phase change materials (PCM). In this study, the effect of utilizing four longitudinal fins and dispersion of TiO2 nanoparticles with different volume fractions on melting of stearic acid as PCM is numerically investigated in the finite volume software, ANSYS FLUENT. The heat storage system is comprised of two concentric pipes with the diameters of 15.88 and 57.88 mm. The inner tube is made of copper and water flows in it as heat transfer fluid (HTF). The results indicated that the melting rate of PCM increases as the volume fraction of nanoparticles goes up. However, the addition of nanoparticles is not much effective in the enhancement of thermal conductivity, and it only improves convection. By adding 0, 1, 2.5, and 5 vol% of TiO2 nanoparticles to PCM, the liquid fractions after 5400 s were 31.6, 32.23, 33.54, and 35.8 respectively. Using fins is a far better option for improving the melting rate of stearic acid, where the liquid fraction of stearic acid after 3600 s for the base case, PCM with 5 vol% of TiO2, and finned tube are 13.38, 14.86, and 81.32 percent, respectively.

Renewable Energy, Thermal Energy Storage, Phase Change Material, Stearic Acid, Nanoparticles, Longitudinal Fins