Experimental Investigation of Temperature Dependent Thermal Conductivity of Aluminum Oxide and CNT Heat Transfer Fluids

Nanofluids often exhibit superior heat transfer characteristics when compared with conventional heat transfer fluids. The increase in thermal conductivity due to the presence of various nanoparticles was experimentally examined using commercially available equipment that utilizes the two thickness method. The thermal conductivity of 10 and 30 nm aluminum oxide nanoparticles suspended in distilled water at concentrations of 2% and 5% was measured for a temperature range of 15°C to 70°C in increments of 5°C. For a 2% concentration of 10 nm aluminum oxide the experimentally derived thermal conductivity deviated from the theoretical thermal conductivity predicted by Maxwell by an average of 1.55%. The average percent increase in the thermal conductivity of the base fluid due to the presence of 10 nm aluminum oxide nanoparticles was found to be 4.17 and 4.90% for concentrations of 2 and 5% respectively. The presence of 30 nm nanoparticles resulted in a greater discrepancy with the theoretical model developed by Maxwell, regardless of concentration. In addition, the presence of 10 nm aluminum oxide nanoparticles resulted in a greater increase in thermal conductivity when compared with 30 nm aluminum oxide nanoparticles. In addition, the thermal conductivity of a base fluid dispersed with multi-walled carbon nanotubes (MWNTs) with an outer diameter ranging from 13–18 nm and a length ranging from 3–30 micrometers (μm) was examined. The presence of a 0.2% concentration of MWNTs resulted in an average increase in thermal conductivity of 0.31%. Unfortunately, there was a large standard deviation in the results for the MWNTs and significant fluctuations with temperature. While this experimental methodology may be sufficient for metal based nanofluid particles it may be undesirable for fluids enhanced by MWNTs.