Surface tension of nanofluid-type fuels containing suspended nanomaterials

Abstract

The surface tension of ethanol and n-decane-based nanofluid fuels containing suspended aluminum, aluminum oxide, and boron nanoparticles as well as dispersible multi-walled carbon nanotubes (MWCNTs) were measured using the pendant drop method by solving the Young-Laplace equation. The effects of nanoparticle concentration and size, and the presence of a dispersing agent (surfactant) on surface tension were determined. The results show that surface tension increases both with particle concentration (above a critical concentration) and particle size for all cases. This is because the van der Waals force between particles at the liquid/gas interface increases surface free energy and thus increases surface tension. At low particle concentrations, however, addition of particles has little influence on surface tension because of the large distance between particles. An exception is when a surfactant was used or when MWCNTs were involved. For such cases, the surface tension decreases compared with the pure base fluid. The hypothesis is that the polymer groups attached to MWCNTs and the surfactant layer between a particle and that the surround fluid increases the electrostatic force between particles and thus reduce surface energy and surface tension. © 2012 Tanvir and Qiao.