Preparation and Characterization of CuO Nanoparticles Dopped Paraffin Wax Composite for Solar Thermal Energy Storage in the Solar Drying Application

Thermal energy storage (TES) systems for solar dryers receive wide attraction as the TES system enhances the performance of dryers. The most promising phase change material (PCM) for TES in solar drying applications is thought to be paraffin wax. However, the performance of the TES is hindered by the low thermal conductivity of paraffin wax. In the present study, composite PCMs comprised of pure paraffin wax and copper oxide (CuO) nanoparticles have been developed with various weight percentages (1, 2, 3, and 4% CuO), and their thermo-physical characteristics were investigated with Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray Analysis (EDAX), Differential Scanning calorimetry (DSC) and Thermogravimetric Analysis (TGA) and Fourier transform Infrared Spectroscopy (FTIR). The FESEM images of 1 and 2% CuO nanocomposite revealed that nanoparticles diffused equally in paraffin wax and formed a sound network, enabling for improved heat transfer within the paraffin wax. However, sample with 3 and 4% CuO nanoparticles suffers from more agglomeration. No foreign molecules were detected in the samples other than the constituents of the CuO in EDAX analysis. DSC heat flow curves for all samples follow a similar pattern, and there are no noticeable alterations at the crest, revealing that the influence of CuO nanoparticle addition on phase change temperature is insignificant. TGA results demonstrate that the dispersion of CuO nanoparticles specifically delays thermal breakdown of nano-CuO–paraffin composites and improves thermal stability. FTIR spectrum has proved that the dispersion of CuO nanoparticles has no effect on chemical bonding with the paraffin. This ensures that nano-CuO–paraffin composites are chemically stable. According to theoretical model calculations, increasing the weight percentage of CuO nanoparticles in pure paraffin wax raises the sample’s thermal conductivity in both the liquid and solid stages. However, except thermal conductivity, the results were not satisfactory when adding nanoparticles above 2% weight fraction due to the localized agglomeration and higher cost of nanoparticles.