Phase-change nanofluids based on n-octadecane emulsion and phosphorene nanosheets for enhancing solar photothermal energy conversion and heat transportation

To offer a solution for low heat transfer and solar energy-storage performance of conventional phase-change fluids, we designed a direct absorption solar energy collecting system based on n-octadecane/phosphorene (PR) nanosheet phase-change nanofluids for capturing solar energy with high energy conversion efficiency and rapid heat response and transfer. The phase-change nanofluids were fabricated through homogenously dispersing PR nanosheets in the n-octadecane aqueous emulsion. The resultant nanofluids exhibit good dispersion stability and suitable viscosity under an optimal emulsifier content of 9.0 wt % and a homogenization rate of 16,000 rpm. Although the nanofluids show a relatively lower latent-heat capacity compared to pristine n-octadecane emul-sion, their thermal response and heat transfer were enhanced significantly due to the introduction of PR nanosheets, leading to an increase in thermal conductivity by 98.59% for the nanofluids containing 1.0 wt % PR nanosheets. More importantly, the n-octadecane/PR nanosheet nanofluids exhibit an excellent optical absorption capacity for solar photothermal conversion and thermal energy storage. The nanofluid containing 1.0 wt % phosphorene nanosheets presents a relative thermal storage capacity of 152% by taking pristine n-octadecane emulsion as a control. The nanofluids also show good working stability for the long-term use in solar photo -thermal conversion and thermal energy storage. The phase-change nanofluids developed in this study exhibit great application potential in solar energy capture and photothermal energy utilization thanks to their enhanced thermal conductivity, high energy-storage density, suitable viscosity, thermal reliability, and excellent photo -thermal conversion and energy-storage capability.