Use of Metal Oxide Nanoparticles to Improve the Thermophysical Properties of R141b Used in Organic Rankine Cycle.

To synthesize and investigate the two kinds of nanoparticles (Al₂O₃ and CuO) dispersed into R141b, nanorefrigerants with the concentrations from 0.5 to 2.4 vol.% were prepared. Thermophysical properties at temperatures from 6 to 22 °C were checked, long-term stability of the nanorefrigerants was also investigated. Results showed that, density and viscosity increased with the increase in nanoparticle volume fractions, however, they decreased with the increase in temperature. Thermal conductivity and thermal diffusivity increased with the augmentation of particle concentration and temperature. Specific heat capacity increased with the increase in temperature, and decreased with the increase in volume fraction of nanoparticles. Based on the measured properties, heat transfer coefficient ratio was calculated to evaluate the heat transfer performance of the nanorefrigerants. Finally, Al₂O₃/R141b nanorefrigerant with 1.2 vol.% was selected as the optimal nanorefrigerant for ORC.