Thermal Performances of Solar Collectors with Advanced Thermal Storage: Analysis of the Effect of Incoming Water in a Double-Pipe Heat Exchanger Incorporating Nanoparticles and Metal Foam

The proposed system is based on a Double-Pipe Heat Exchanger (DPHX)-based Latent Heat Storage Units (LHSUs) that uses Phase Change Material (PCM), whereas the incoming water conditions play a primary role in the charging and discharging of the storage system. In this particular application, it is also crucial to emphasize that enhancing storage capabilities heavily relies on addressing the low thermal performances exhibited by most PCMs. Consequently, materials that boost thermal conductivity, like porous metal foams (specifically, aluminum foam with 20 PPIs and 0.88 porosity), geometry modifications, and dispersion of nano-sized powders (specifically, MWCNT-0.04) into paraffin (specifically, RT82), have been utilized in PCM-based energy storage systems to improve their performances. The predictive model for PCM melting/ solidification has been built up with references to the enthalpy-porosity approach. The research outcomes have been consolidated to encompass aspects such as the liquid phase ratio, temperature variations, energy storage/harvesting rates, and dimensionless factors across different altered Stefan numbers. These modified Stefan numbers represent diverse incoming water conditions, serving as input parameters for assessing the thermal performance metrics, including melting/solidification durations and stored/released energy quantities. Also, the addition of both techniques in the DPHX reduces melting/solidification time and increases the rate of energy storage/harvesting when compared to DPHX with pure PCM. Finally, it is shown that the average storage/harvesting heat rate for DPHX with nanoparticles and metal foams is higher than Pure PCM while the average storage/harvesting heat rate for HTF with a higher Ste number, say different water flow conditions.