Melting enhancement in triplex-tube latent thermal energy storage system using nanoparticles-fins combination

Abstract

Latent thermal energy storage based on Phase Change materials (PCMs) offers a promising solution for correcting the problem of availability of intermittent energy from renewable sources like solar, wind, etc. PCMs have the potential to store large amounts of energy in relatively small volumes and within nearly isothermal processes. However, a major drawback of today's PCMs is that their low thermal conductivity values critically limit their energy storage applications. Also, this grossly reduces the melting/solidification rates, thus making the system response time to be too long. In this study, three enhancement techniques: fins, nanoparticles and a combination of both were investigated with the aim of correcting this limitation. A numerical study based on enthalpy method was used to comparably examine the effects of these techniques on the PCM melting rate in triplex-tube latent heat storage system. A mathematical model that takes into account the natural convection and the Brownian motion of nanoparticles was formulated and successfully validated against previous experimental data. The influence of using different dimensions of fin and different nanoparticle volume fractions on evolution of the solid-liquid interfaces, distribution of isotherms, and temporal profile of liquid fraction over the whole melting process was studied and reported. The results indicate that PCM melting is improved by using these techniques studied. Also it was found that the use of fins alone is better than using either nanoparticles alone or a combination of fins and nanoparticles. The use of longer fins with smaller thicknesses is recommended so as to improve phase-change heat transfer and minimize the volume occupied in the energy storage space.