Thermocapillary flow of thin Cu-water nanoliquid film during spin coating process

Unsteady flow of thin Cu-water nanoliquid film over a horizontal rotating disk is studied numerically using finite difference technique under the assumption of planar interface. It is also assumed that the disk is cooling axisymmetrically from below. The effects of the nanolayer thickness and nanoparticle radius are considered for investigation. It is found that the film thinning rate decreases with increase of the nanoparticle volume fraction. It is also found that thickness of liquid decreases with increase of the thermocapillary parameter. The results show that the rate of film thinning is more for the thermal conductivity model of Yu and Choi [47] compared to the model of Maxwell [46]. It is observed that the film thinning rate increases with increase of nanolayer thickness but it decreases with the nanoparticle radius. A curve R ¼ Rcðz; tÞ in R z plane is delineated along which temperature gradient Tz is zero and positive or negative according to R/ Rc or R [Rc respectively. Furthermore, it is shown that the region for Tz [0 enlarges with increase of the nanoparticle volume fraction and the nanolayer thickness.