Effect of particle size on the thermal conductivity of nanofluids containing metallic nanoparticles

Abstract

A one-parameter model is presented for the thermal conductivity of nanofluids containing dispersed metallic nanoparticles. The model takes into account the decrease in thermal conductivity of metal nanoparticles with decreasing size. Although literature data could be correlated well using the model, the effect of the size of the particles on the effective thermal conductivity of the nanofluid could not be elucidated from these data. Therefore, new thermal conductivity measurements are reported for six nanofluids containing silver nanoparticles of different sizes and volume fractions. The results provide strong evidence that the decrease in the thermal conductivity of the solid with particle size must be considered when developing models for the thermal conductivity of nanofluids.

Figure 1

Size dependent thermal conductivity of copper. The solid line represents the thermal conductivity of copper nanoparticles calculated using Equations 3 and 5. The dashed line represents the bulk thermal conductivity of copper at 298 K. Data points are for copper thin films [18]

Figure 2

SEM/TEM images of the silver nanoparticles provided by Nanostructured and Amorphous Materials, Inc. (Los Alamos, NM, USA). (a) 20 nm, (b) 30-50 nm, and (c) 80 nm

Figure 3

Effect of particle size on the thermal conductivity of nanofluids containing silver nanoparticles. Points (1% black square, 2% black circle) represent experimental data of this work. Dashed (1% ― ―, 2% ----) and solid lines represent calculated values assuming size dependence and without size dependence, respectively