ISSN Online: 2688-7231
ISBN Online: 978-1-56700-524-0
Proceedings of the 26thNational and 4th International ISHMT-ASTFE Heat and Mass Transfer Conference December 17-20, 2021, IIT Madras, Chennai-600036, Tamil Nadu, India
Simulation of spreading of a water droplet on a partially wetted substrate at a low Weber number using an improved contact angle model
Spreading of a water droplet on a hydrophilic glass substrate at a low Weber number is of interest in the present study. The spreading dynamics of interest are the shape evolution over a thin air film, sudden collapse of the air film, and the subsequent spreading of the liquid droplet. The modeling perspective that can correctly simulate droplet and the determination of its initial shape are discussed. In this regard, the initial shape is extracted from experiments and subsequently utilized in COMSOL simulation to determine shape contours during spreading. Numerical simulation is performed with the dynamic contact angle model prescribed as a boundary condition at the three phase contact line. The parameters involved in the contact angle model have been evaluated from experiments. The present formulation of the contact angle hysteresis leads the contact angle model to successfully track damped oscillations of the droplet during its spreading phase. The effect of substrate heating on the air film and subsequent droplet spreading are also examined. In these experiments, the ITO coated side of the glass substrate is maintained at 90°C by resistive heating. A K-type thermocouple is used to control and monitor temperature. Experiments showed that heating did not change the spreading dynamics as long as the drop rested initially on the air film. However, in the long run, elevated temperatures had the effect of reducing the wettability of the surface.