Thermal performance improvement of energy storage materials for low operating temperature solar water heating systems

Abstract

Recent studies have shown the attractive energy storage capabilities of phase change materials (PCMs); however, PCMs may not be fully effective due to their poor heat transfer characteristics. Moreover, the melting point of PCMs restricts direct integration into a solar collector for low operating solar water heating (SWH) applications. This study investigates the heat transfer enhancement of PCMs as well as aiming to lower their melting point onset to expedite the latent heat storage initiation. The selected types of PCMs are paraffin waxes with melting point temperatures of 28–72 °C. In Phase I, silicone oil is selected as a heat transfer medium to be used with the PCMs to establish natural convection enhancement, which led to maximum melting point depression of approximately 3 °C in the PCM72. In Phase II, the conductive heat transfer enhancement was studied by adding nanoparticles with varying mass concentrations. From this analysis, it was determined that PCM72 with 1% multi-walled carbon nanotubes (MWCNT) has shown an increase of approximately 3.81% in thermal conductivity. The obtained results from this study can lead to overall efficiency improvement of SWH systems by employing the PCM mixtures with low melting point, while keeping the high latent heat capacity, and high thermal conductivity.