Influence of the surface temperature on the spreading and receding dynamics of an impacting biodiesel drop

The paper presents an experimental study of the impact of a Jatropha biodiesel drop on a heated flat stainless steel surface at various temperatures and Weber numbers (We). The effect of the surface temperature (T-S) on the spreading and the receding of the drop is explored. Entire impact process is recorded using a high-speed camera and the captured images are processed to obtain the evolution of the drop profile and impact morphology at various surface temperatures. The analysis of the morphology provides physical changes in the drop during impact. The maximum spreading factor, beta(max) (maximum spreading diameter normalized by pre-impact diameter), increases with both We and T-S. The receding is found to be dependent on the surface temperature. The average velocity of the receding increases with T-S, because of the decrease in surface free energy at higher temperatures. The decrease is explained from the measurement of the temperature-dependent static contact angles. The non-dimensional time taken to reach beta(max) increases with T-S and this increment is more pronounced at higher We. beta(max) is found to be highly sensitive to We and shows a sharp rise at higher surface temperatures.