Measurements of the contact angle of nanofluids and development of a new correlation

Abstract

Contact angle measurements were performed on deionized water, propylene glycol and mixture of 60% propylene glycol and 40% water by mass (60:40 PG/W), over a temperature range of 25°C to 40°C. All measurements were performed on the surface of a glass slide at the solid–fluid–air-interface. After confirming the contact angle value of water with the data of other researchers, the same procedure was applied to four nanofluids (nanoscale particles dispersed in a base fluid) containing aluminum oxide (Al2O3), zinc oxide (ZnO), titanium dioxide (TiO2) and silicon dioxide (SiO2) nanoparticles dispersed in 60:40 PG/W. For the nanofluids, the particle volumetric concentrations were varied from 0 to 6% and the average particle sizes ranged from 15 to 50nm. From the experimental data, it was observed that the contact angles of three single phase liquids and four nanofluids were less than 90°, indicating that all these fluids were wetting to the glass surface. The contact angles of all tested fluids exhibited a continuous decrement with an increase in temperature, and a linear equation for contact angle with temperature matched the data well. For the nanofluids, an increase in the particle volumetric concentration caused a decrease in the contact angle at a constant temperature. The variation of the contact angle followed a second order polynomial relation with the volumetric concentration. For nanofluids at the same volumetric concentration and the same temperature, the contact angles were observed to be lower for larger particle sizes, except for the ZnO nanofluid. A statistical analysis performed on the experimental data yielded a correlation suitable to represent all the nanofluids tested. This contact angle correlation is a function of temperature, volumetric concentration and the size of the nanoparticles, which predicts results successfully with an average deviation of 6.3% from the measured values.