Effects of alignment, pH, surfactant, and solvent on heat transfer nanofluids containing Fe2O3 and CuO nanoparticles

In this paper, the effects of alignment, pH, surfactant and solvent on heat transfer nanofluids containing Fe2O3 and CuO nanoparticles are studied and analyzed. The microscope images show that Fe2O3 could form some kind of alignment spontaneously in water even without external magnetic field. With the addition of external magnetic field, the alignment is strengthened. In water, the magnetic particle agglomeration to larger size occurs easily, which makes the directional alignment much faster and easier. Ethylene glycol solvent and chemical surfactant sodium dodecyl benzene sulfonate, NaDDBS could separate the Fe2O3 and CuO nanoparticles well in the fluids and avoid possible aggregation. Therefore, magnetic alignments are hard to observe. The measured thermal conductivities of each individual sample coincide with the microscope images and assumptions. In addition, pH values of Fe2O3 and CuO nanoparticles are measured and it has been determined that at those pH values, thermal conductivities of those nanoparticles would not be influenced according to the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The highlight of this paper is that our microscope images could well explain most of the literature data and conclusions and may open new door to better understanding fundamental nature of nanofluids. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3694676]