Melting of PCM with Nanoparticles in a Triplex-Tube Thermal Energy Storage System

Environmental concerns and limited energy supply today makeenergy storage very important, especially in solar energy utilization. The latent heat storage method has the advantage of storing a large amount of energy in a relatively small volume. Achieving thermal energy storage with latent heat application using phase- change materials (PCMs) involves the heat of fusion at the solid- liquid phase transition. The problem with today's PCMs is that their very low thermal conductivity values severely limit their energy storage capability. This also makes the melting and solidification times too long for meetingthedesiredresults. Investigations to solve thisproblem include improved design configurations and addition of nanoparticles to thePCMto enhance the thermal conductivity. This study is on the effects of nanoparticle dispersion in the melting of a PCM in a triplex- tube heat exchanger heated under constant surface- temperature conditions. The governing equations for the configuration and process were discretized via the finite volume method and solved numerically. The developed model, which was validated, shows good agreement when compared to a previous related experimental study. The computations were performed for nanoparticle volume fractions ranging from 1% to 3%. The results, shown in the form of isotherms and contours of the solid- liquid interface over different periods of charging time, are presented and discussed. Theresultsshowanenhancement in the melting rate with doping nanoparticles of different volumetric concentrations. The results also show melting time savings of 17% as a result of adding nanoparticles to the PCM for a nanoparticle volume fraction of 1%. Higher- volume fractions were found to not result in significant melting time savings for the process in the triplex- tube heat exchanger.