Measurements of the surface tension of nanofluids and development of a new correlation

Surface tension measurements were performed on four nanofluids containing aluminum oxide (Al2O3), zinc oxide (ZnO), titanium dioxide (TiO2) and silicon dioxide (SiO2) nanoparticles suspended in a base fluid of 60% propylene glycol and 40% water by mass (60:40 PG/W). First, benchmark tests for the surface tension of water were performed, for which accurate data are available in the published literature. Measured data agreed well with the published data confirming the accuracy of the apparatus, as well as the experimental procedure. Following the benchmark tests, measurements were performed on nanofluids over a temperature range of 30 degrees C to 70 degrees C for particle volumetric concentrations ranging from 0 to 6 % and particle sizes in the range of 15-50 nm. From the experimental data, it was observed that the surface tension of nanofluids decreased with an increase in temperature. At a constant temperature, an increase in the particle volumetric concentration of a nanofluid caused a decrease in the surface tension. For nanofluids at fixed volumetric concentration and temperature, the surface tension was found to be lower for smaller particle sizes except the ZnO nanofluid. A statistical analysis performed on the experimental data yielded a single correlation valid for all the nanofluids tested. This surface tension correlation is a function of temperature, volumetric concentration and the size of the nanoparticles, which predicts results successfully with an average deviation of 2.6% from the measured values. (C) 2015 Elsevier Masson SAS. All rights reserved.