Mean-Field Versus Microconvection Effects in Nanofluid Thermal Conduction

Transient hot-wire data on thermal conductivity of suspensions of silica and perfluorinated particles show agreement with the mean-field theory of Maxwell but not with the recently postulated microconvection mechanism. The influence of interfacial thermal resistance, convective effects at microscales, and the possibility of thermal conductivity enhancements beyond the Maxwell limit are discussed.

Figure 1

THW data for the thermal conductivity of Ludox suspensions (squares) and MFA suspensions (circles) compared with the Maxwell model with $R_b=0$ (dotted lines) and microconvection model [9] with $R_b=2.5\times {10}^{-8}\mathrm{K}{\mathrm{m}}^2{\mathrm{W}}^{-1}$, $\gamma =2.5$, $A=4\times {10}^4$ (solid lines). The uncertainty in the experimental data is within $\pm 3\%$.

Figure 2

THW data for Ludox ($\rho \sim 2200\mathrm{kg}/{\mathrm{m}}^3$, $d=32\mathrm{nm}$), MFA ($\rho \sim 2140\mathrm{kg}/{\mathrm{m}}^3$, $d=44\mathrm{nm}$), ${\mathrm{Al}}_2{\mathrm{O}}_3$ ($\rho \sim 4000\mathrm{kg}/{\mathrm{m}}^3$, $d=38\mathrm{nm}$) [15] and CuO ($\rho \sim 6300\mathrm{kg}/{\mathrm{m}}^3$, $d=29\mathrm{nm}$) [15] suspensions, plotted as a function of $\beta \varphi$. The deviation of the microconvection model [9] from Maxwell for ${\mathrm{Al}}_2{\mathrm{O}}_3$ and CuO are comparable to the experimental uncertainty (results not shown).