Heat transfer characteristics of fluids containing paraffin core-metallic shell nanoencapsulated phase change materials for advanced thermal energy conversion and storage applications

The influence of heat transfer characteristics of fluids filled with paraffin core-metallic shell nanoencapsulated phase change material (PCM) on photothermal conversion and storage in a volumetrically heated solar system is numerically analysed. The results show that nanoencapsulated paraffin/Al, paraffin/Au, paraffin/Ag, and paraffin/Cu filled heat transfer fluids enhance the energy storage by 68, 73, 92 and 86 %, respectively as compared with the water-based Al, Au, Ag and Cu nanofluids. It is found that the phase change slurry (PCS) improves the temperature and storage gain, as the utilization of nanoencapsulated PCM and the rise in PCM mass concentration enhance the solar energy absorption power of the slurry. The maximum enhancement in stored energy is also observed for paraffin/Cu PCM filled slurry for a particle diameter of 15 nm. The enhancement in mass concentration of paraffin from 5 to 20 %, improves the thermal performance from 312 to 554 % compared to pure water, respectively. Increasing the size of the core/shell architecture of the PCM, however, reduces the surface area-to-volume ratio of the capsule, causing aggregation of the particles and decreasing the heat transfer between the capsule and the host fluid. This in turn results in decrease in temperature gain. Furthermore, it is noticed that the merger of mono- and hybrid- nanoparticles augments the thermal performance of the PCS. The findings of the study indicate that the paraffin core-metallic shell nanoencapsulated PCMs would significantly enhance the performance of advanced photothermal energy conversion and storage devices.