Direct Photo-Thermal Energy Storage Using Nanoparticles Laden Phase Change Materials

Abstract

In the present work, we propose thermal energy storage by direct photo-thermal energy conversion (referred to as optical charging) using nanoparticles laden phase change materials (PCMs). In the conventional thermal storage systems, the absorbed solar energy is indirectly transferred to the PCM (primarily through conduction and convection heat transfer mechanisms) and is subsequently stored in the form of latent heat of the PCM (referred to as thermal charging). Opposed to the conventional thermal storage strategies; optical charging involves direct interaction of the sunlight with the phase change material (radiation being the predominant heat transfer mechanism). Broad absorption-based nanoparticles (amorphous carbon) have been seeded into the pristine phase change material (paraffin wax) to enhance photo-thermal conversion efficiency. Particularly, we investigate the effect of adding nanoparticles to conventional PCMs during optical charging process. To understand the role of nanoparticles; samples of pristine paraffin wax and nano-PCMs [different concentrations of nanoparticles (0.05, 0.1, 0.2, 0.4%, wt%) dispersed in the pristine paraffin wax] have been optically heated. Furthermore, optical charging has been compared with the conventional thermal charging process. As per the experimental observations, the optical charging scheme significantly improves the thermal charging rate (by more than 157%) at optimum nanoparticle concentration (0.2%, in the present study) as compared to conventional thermal charging.