Effect of surfactant on the rheological behavior and thermophysical properties of hybrid nanofluids

Abstract

Adding surfactant can improve the stability of hybrid nanofluids. However, positive or negative effects of the surfactant on the thermophysical properties of hybrid nanofluids should be further investigated. In the present study, effects of different surfactants, including SDS, PVP and CTAB, with various mass concentrations and temperatures on the stability of Al2O3-CuO/Water (W) and Al2O3-TiO2/Water (W) hybrid nanofluids are investigated. Results show that increment of surfactant concentration improves the stability and viscosity. Then obtained results from UV–Vis Spectrophotometer, TEM and sedimentation methods are compared, and PVP surfactant has the highest degree of stability, with the minimal sedimentation up to 25 days. At the optimum PVP surfactant concentrations of 0.005 wt% and 0.01 wt%, the maximum thermal conductivity enhancement is 12% and 14% at 60 °C for Al2O3-CuO/W and Al2O3-TiO2/W hybrid nanofluids. Therefore, adding even little amount of surfactant can improve the stability and thermal conductivity of hybrid nanofluids.