Particle-shape-, temperature-, and concentration-dependent thermal conductivity and viscosity of nanofluids

In this study, using the Green-Kubo-method-based molecular dynamics simulations, correlations for predicting the thermophysical properties of nanofluids are developed based on particle shape, fluid temperature, and volume concentration. Silver nanofluids with various nanoparticle shapes including spheres, cubes, cylinders, and rectangular prisms are investigated. The numerical study is conducted within the concentration range 0.14–1.4 vol % and temperature range 280–335 K. The relative thermal conductivity and relative viscosity predicated by the proposed correlations are within a mean deviation of 2% and 5%, respectively, as compared with the experimental results from this study and the available literature. The proposed correlation will be a useful tool for engineers in designing the nanofluids for different applications in industry.

Figure 1

Silver particles with different shape to be inserted in the MD simulation box filled with water.

Figure 2

Schematic drawing of the circumscribing and equivalent circles around a cylindrical nanoparticle.

Figure 3

Experimental measurement of relative thermal conductivity of spherical silver nanofluids versus (a) temperature at a volume concentration of 0.6 vol % and (b) volume concentration at a temperature of 293 K.

Figure 4

Experimental measurement of relative viscosity of spherical silver nanofluids versus (a) temperature at a volume concentration of 0.6 vol % and (b) volume concentration at a temperature of 293 K.

Figure 5

Relative thermal conductivity versus particle elongation of silver nanofluid at temperature 300 K and 1 vol %.

Figure 6

Relative thermal conductivity versus (a) surface area-based sphericity and (b) volume-based sphericity of silver nanofluid at temperature 300 K and 1 vol %.

Figure 7

Relative thermal conductivity versus surface area to volume ratio for different particle shapes of silver nanofluid at temperature 300 K and 1 vol %.

Figure 8

Viscosity versus viscosity shape factor in the (a) $x$ direction (b) $y$ direction, and (c) $z$ direction for three values of α.

Figure 9

Experimental measurement of the effect of temperature on the relative thermal conductivity of spherical silver nanofluid with 1.0 vol % concentration; the effect of temperature on volume concentration is neglected.

Figure 10

Experimental measurement of the effect of the particle volume concentration on the relative thermal conductivity of spherical silver nanofluid at a temperature of 300 K; the effect of temperature on volume concentration is neglected.

Figure 11

Experimental measurement of the effect of temperature on the relative viscosity of spherical silver nanofluid at 1 vol %; the effect of temperature on volume concentration is neglected.

Figure 12

Experimental measurement of the effect of particle volume concentration on the relative viscosity of spherical silver nanofluid at 300 K.

Figure 13

Comparison of the MD simulation data with data predicted using Eq. (20).

Figure 14

Comparison of the relative TC data predicted by the proposed model and existing models with the data from the literature and the present experiment at different $S/V\left({\AA }^{-1}\right)$ and volume concentrations at $T=293\mathrm{K}$.

Figure 15

Comparison of the relative TC data predicted by the proposed model with the measured data from the literature and the present experiment at different temperatures and volume concentrations.

Figure 16

Variation of the relative thermal conductivity with different $S/V$ (${\AA }^{-1}$).

Figure 17

Comparison of the simulation data with the data predicted by Eq. (30).

Figure 18

Comparison of the relative viscosity data predicted by the proposed model with those in the literature and our experiment at different values of $m$ and volume concentrations.

Figure 19

Comparison of the relative viscosity data predicted by the proposed model with those in the literature and present experiment at different temperatures and volume concentrations.

Figure 20

Variation of relative viscosity at different values of $m$.