Search

Jatropha curcas biodiesel was taken as the research object, studied the single and compound effects of oxidation degree and temperature on kinematic viscosity of biodiesel, and established a mathematical model. The results indicate that the kinematic viscosity of biodiesel decreases gradually with the increase of temperature, and the mathematical model affected by the single factor of temperature is η = e(A + Bt + Ct2) . The kinematic viscosity of biodiesel increases with the increase of oxidation time. The regression equation between kinematic viscosity and conductivity is established as follows: η = A + Bμ. It is found that the influence of temperature on the kinematic viscosity of biodiesel is much greater than that of oxidation, and the higher the temperature, the lower the influence of oxidation on the kinematic viscosity of biodiesel. Through the analysis of the influence weight of two factors and the change rate of kinematic viscosity, it is found that with the increase of temperature, the effect of conductivity on the change rate of kinematic viscosity of biodiesel is positive, but the influence decreases gradually. The relationship between kinematic viscosity, temperature and oxidation

Utilizing nanorefrigerants as working fluids can significantly enhance the energy efficiency of low‐temperature waste heat recovery systems (≤ 50°C). Refrigerants with low viscosity and density require a substantial amount of surfactant to maintain a stable suspension of nanoparticles. However, the excessive use of surfactants, which have a notably low thermal conductivity, could lead to foam generation and reduce heat transfer coefficient. High viscosity lubricating oils with small amount of surfactant can prolong the stable suspension time and produce repulsive force. Therefore, a new combination of them improves the stability of TiO2/R141b nanorefrigerants. Additionally, viscosity and thermal conductivity of the nanorefrigerants were optimized using an implementation of a modified non‐dominated sorting genetic algorithm (NSGA‐II). The results show that adding lubricating oil inhibits aggregation of the nanoparticles leading to a stable suspension for more than 6 h at volumetric mixing ratios (lubricating oil: refrigerant) greater than 1:30. The best dispersion stability was achieved at surfactant polyvinyl pyrrolidone (PVP) mass ratio of 0.5, and the average absorbance value was increased by 65.45%. Compared with pure refrigerants, the thermal conductivity of TiO2/R141b (0.15 vol.%) nanorefrigerant was enhanced by up to 12.59% under the optimum mixing ratio. Moreover, the studied nanorefrigerants exhibited shear thickening behavior throughout the studied shear rate range, with increased non‐Newtonianization with decreasing temperature. Finally, the Pareto points were divided into three representative groups based on thermal conductivity and viscosity. These findings suggest enhanced high heat transfer efficiency with pumping power of nanorefrigerant in the waste heat recovery systems. [ABSTRACT FROM AUTHOR]