Experimental study on the spreading length of liquid film induced by single water drop impinging on inclined cylindrical surface

Abstract

The spreading and shrinking processes of the liquid film caused by the impingement of water drop on an inclined cylindrical surface are two important aspects reflecting the dynamic behavior. In this paper, the parametric effects of the liquid film spreading and shrinking processes were investigated by using an experimental approach. The time-dependent evolutions of the dimensionless spreading lengths (axial and circumferential) under various impingement situations were indirectly derived by image post-processing. It is discovered that, when the cylinder is tilted, the liquid film will go through one more stage in the spreading process compared with when it is horizontal, i.e., the sliding stage, which facilitates the spreading of water drop into a larger liquid film. The time at which the spreading lengths in the axial and circumferential directions reach their maximum is not consistent and determined by the inclination angles. There is a critical angle of 35°, which changes the relative magnitude between the maximum axial and circumferential spreading factors. Due to the breakage of the liquid film edge during shrinking process, satellite drops are more likely to form when the cylinder is tilted than when it is horizontal. The Weber number and inclination angle exert substantial influence on both the spreading and shrinking processes of the liquid film. However, the impact of the cylindrical surface temperature appears to be comparatively insubstantial. Finally, the correlations of the maximum and stable spreading factors were fitted. Among them, the mean relative deviations of the maximum circumferential and axial spreading factors are 12.2 % and 7.4 %, respectively, compared with the simulated and experimental data of single water drop impinging on horizontal cylindrical surfaces from other studies.