Experimental investigation of spreading and receding behaviors of Newtonian and viscoelastic droplet impacts on inclined dry surfaces

Drop impact on solid surfaces are widely used in oil and gas industries, surface painting, hot surfaces cooling, and agricultural products spraying. In this study, spreading and receding factor related to non-Newtonian (Boger) fluid droplets on dry inclined surfaces (such as Plexiglas and stainless steel) was laboratory tested and compared with Newtonian fluids (water, glycerol and their solution). Here, drop impacts were investigated for two impact angles (60° and 75°) at Weber numbers ranging from 245 to 545. The study aimed at evaluating the effects of impact velocity, impact angle, surface wettability, fluid viscosity, and elasticity on the dynamic behaviors of Newtonian and Boger droplets in spreading and receding stages. The results showed that with an increase in the impact velocity (growth of We), the drop was further expanded, the spreading velocity was increased, and the value and velocity of receding were incremented. By decreasing the drop impact angle, the effects of impact velocity and fluid viscosity on spreading and receding velocities were reduced at the back of the impact point. In the front zone, the drop reached maximum length of spreading and minimum length of receding over a longer period by decreasing the impact angle. On the other hand, with a decrease in the fluid viscosity, spreading velocity was increased, and maximum spreading occurred over a longer period. The surface wettability also played an important role in the receding stage for droplets with low viscosities. As fluid elasticity rose, both velocity and maximum spreading were reduced, while the value and velocity of receding were increased.