Experimental study of dripping, jetting and drop-off from thin film flows on inclined fibers

Abstract

Gravity driven film flows on vertical fibers are known to exhibit a variety of flow dynamics including the formation of droplet trains induced by the hydrodynamic (Kapitza) and Plateau–Rayleigh instability mechanisms. Through an experimental study, it is shown how inclination of the fiber from the vertical influences these dynamics. The formation of waves, regime transitions from dripping to jetting regimes, as well as the onset of drop-off in the form of droplet detachment from the fiber are illustrated and described in dependence of the fiber inclination angle and the liquid mass flow rate. Additionally, the influence of fiber diameter and nozzle geometry on regime transitions and the onset of drop-off from the substrate are examined. It is shown that the onset of drop-off is strongly related to the transition from a regime characterized by a regular wave pattern to a regime characterized by an irregular wave pattern. It is also demonstrated that this regime transition depends not only on flow rate and fiber geometry, but also strongly on the inclination angle. Interestingly, a stabilizing effect of increasing the fiber inclination is detected for constant fiber geometry and film flow rate.