Experimental investigation on dynamic behavior of single droplet impcating normally on dry sphere

Abstract

The phenomenon that droplets impacting on the solid surface is ubiquitous in industrial applications such as spray cooling, spray painting, ink-jet printing, and fuel-air mixing internal combustion engines. The dynamic of droplet impacting on solid surface has been a hot topic in the area of fluid mechanics. Most of the existing experimental studies focused on the droplet impacting on flat or cylinder surface whereas the droplet impacting on a dry sphere surface, especially its effect from the sphere curvature, has been less investigated. Therefore, the dynamic behavior of a droplet impacting normally on a dry sphere is experimentally investigated at the relatively high Reynolds and Weber number in the present work. The impacting velocity of the droplet on the sphere is discussed with consideration of air resistance effect. The influences of spherical curvature and Weber number on the dynamic behavior and spreading factor are analyzed. The experimental results are compared with those of previous impacting flat researches. The results show that the drop velocity fluctuates significantly near the impacting sphere. The influence of the spherical curvature on the dynamic behavior of the droplet impact is obvious. The maximum spreading diameter of the liquid film will exceed that of the sphere with a curvature greater than 0.2 mm<sup>–1</sup>, and some segments of the liquid film rim even slide down directly. When the spherical curvature is less than 0.167 mm<sup>–1</sup>, the dynamic behaviors of the impacting droplet will undergo the spread, retraction, oscillation, and stable attachment after impacting. Then the maximum spreading factor of the droplet impacting sphere is little influenced by the curvature, and gradually tends to that of the droplet impacting plane with curvature decreasing. The Weber number has little influence on the spreading velocity of the liquid film, but obvious on the retraction. The maximum spreading factor gradually increases with Weber number increasing. A simple empirical correlation for the maximum spreading factor is obtained. This study conduces significantly to further investigating the dynamic characteristics of droplets impacting on the sphere.

Icing characteristics of the superhydrophobic surface of gas turbine fairing

“…When the wall temperature is -25~5ႏ, there will be rebound and crushing phenomenon. In their study, Tang et al [8] looked at how a droplet moves when it hits a sphere at a high Weber number, and the results showed that when the curvature į 0.167 mm -1 , a completely dynamic process occurs after the impact; when the curvature 0.167 mm -1 į 0.2 mm -1 , droplets cover almost the entire surface; when the curvature į 0.2 mm -1 , some of the droplets will slide off the sphere.…”