The influence of surfactant and ultrasonic processing on improvement of stability, thermal conductivity and viscosity of titania nanofluid

Nanofluid, as a brand new cooling fluid, is a colloidal suspension which enhances the heat transfer but its stability and durability are matters of concern for the industrial applications in the future. The aim of this research is to investigate the stability of titania nano-suspensions by comparing the effect of surfactant addition and ultrasonic processing. In the present research, six different nanofluids with 0.1 wt.% loading of TiO2 nanoparticles (25 nm diameter) were prepared using a two-step method. Ultrasonic processing (i.e. bath and horn) were applied to help the homogeneity and Sodium Dodecyl Sulfate (SDS) as anionic surfactant was added to monitor the stability of the samples. UV-vis spectrometry, particle size distribution, zeta potential, Transmission Electron Microscopy (TEM) and sedimentation photo capturing were applied to visualize the stability and sedimentation rate of the prepared nanofluids. In addition, thermal conductivity and viscosity of these six samples were measured. The optimized nanofluid was selected in terms of better stability, thermal conductivity and viscosity. The results revealed that 3-h ultrasonic bath process with the addition of 0.1 wt.% of surfactant can be the most stable suspension with the highest thermal conductivity for further applications within 1 month.