Thermal Performance of Selected Nanofluids with Surfactants

Nanofluids have been proposed for use as working fluids in order to increase energy efficiency. While a large number of studies have been performed, there is comparatively high variation in reported physical property and heat transfer enhancement data. In addition, comparatively few thermal enhancement studies consider the effects of surfactants that may be required to ensure sufficient stability of the nanofluid over time. In this study, nanofluids were prepared by combining different nanoparticles, base fluids and surfactants and were subsequently evaluated for stability using the sedimentation method. Based on the sedimentation trials and viscosity measurements, three nanofluids (aluminium oxide/water; activated carbon/CTAB/water; copper oxide/ARB/water) were selected for thermal performance enhancement experiments. Thermal enhancement performance was tested in a closed loop with two double pipe heat exchangers and all physical properties required in the calculations were measured directly as part of this study. The carbon/CTAB/water nanofluid had the highest heat transfer enhancement index (a comparison of increased heat transfer rate against increased pressure drop) of the three nanofluids considered. Sedimentation of nanoparticle agglomerates was most noticeable with the aluminium oxide/water nanofluid that did not contain a surfactant.