Experimental investigation on photothermal properties of Zn-ZnO/paraffin hybrid nanofluids

As one of the phase change materials (PCMs), paraffin is widely used in solar energy storage and utilization; however, there are limitations to its use due to poor photothermal properties of paraffin with low thermal conductivity and weak spectral absorption. In this present work, an experimental investigation on improving the photothermal properties of PCMs by producing hybrid PCM-based nanofluid with paraffin wax incorporating zinc (Zn) and zinc oxide (ZnO) nanoparticles was carried out. The two-step method was considered for the preparation of the Zn-ZnO/paraffin hybrid nanofluid, and the thermal and optical properties of the hybrid nanofluid were experimentally investigated. The impacts of nanoparticle concentration and solar radiation intensity on the photothermal properties of hybrid nanofluid were also studied. The results show that the addition of Zn and ZnO nanoparticles enhances thermal conductivity and specific heat capacity compared with pure paraffin. On the other hand, the transmission of nanofluid reduces with optical length and nanoparticles concentration increasing. Zn-ZnO/paraffin hybrid nanofluid can promote the photothermal properties in lower concentrations and higher irradiance range, and the maximum photothermal conversion efficiency of Zn-ZnO/paraffin hybrid nanofluids is 42.97%.