Experimental investigation of TiO2/water nanofluid droplet impingement on nanostructured surfaces

This paper presents the results of an experimental investigation of nanofluid droplets impacting on nanostructured surfaces. Nanofluids with required weight concentration of 0.25-0.75 wt % were prepared by dispersing TiO2 (21 nm) nanoparticles and appropriate amounts of sodium dodecyl sulfate (SDS) surfactant in Milli-Q water. Superhydrophobic and superhydrophilic coatings were applied over a silicon substrate. The images obtained from the high-speed camera clearly show that when a nanofluid droplet impacts a superhydrophobic surface at room temperature, it spreads, retracts, oscillates, and continues to retract to approximately its initial size. In addition, the increase in nanofluid concentration leads to a decrease in the maximum spreading and the height of droplets after impingement. Also, the use of nanofluids increases the temperature difference at the center of the droplet impact region. TiO2 nanoparticles improve the cooling effectiveness of the droplets on uncoated and superhydrophobic surface up to 33% and 214%, respectively.