A model reported by the present investigators has earlier shown that the extent of heat pick up by a nanoparticle during its collision with the heat source in a given nanofluid would depend on the thermal conductivity (kp, unit W/m.K), density (ρ, unit kg/m3), elastic modulus (E, unit GPa) and Poissons ratio (μ) of the nanoparticle and heat source. Considering the expression for collision period and thermal conductivity of nanoparticle, a factor χ =kp(ρ/E)0.4 is proposed here and examined for the preliminary identification of the potential of a dispersoid in enhancing the thermal conductivity of a nanofluid. The χ-factor for Ag, Cu, CuO, Al2O3 and SiO2 are 2960, 2247, 116, 14.1 and 5.5, respectively. The higher χ-factor of CuO compared to that of Al2O3 can explain why water and ethylene glycol (EG) based CuO-nanofluid is reported to show higher enhancement in the thermal conductivity, when compared to similar Al2O3-nanofluid. The χ for SiO2 is much smaller than that for Ag, which also corroborates well with the marginal enhancement in thermal conductivity of water based nanofluid containing SiO2 nanoparticles. Therefore, a high value of χ of the nanodispersoid can serve as a parameter for the design of nanofluids for heat transfer applications.
Numerical analysis of unsteady 3D flow of Carreau nanofluid with variable thermal conductivity and heat source/sink
