Hydrodynamics and morphologies of droplets coalescence on fiber

Abstract

Fiber coalescence is an effective oil-water separation technology. In this article, the micro-coalescence process of droplets on fiber was studied through high-speed camera technology, and the hydrodynamics and morphology evolution in the process of droplet-fiber coalescence were explored and compared with non-fiber system. The results show that the change of the droplet surface morphology is local at the initial stage of the coalescence process. The droplet morphology changes obviously near the neck. The growth rate of the liquid bridge and the propagation speed of capillary wave in droplet-fiber system are higher than those in non-fiber system. At 0.8 ms, the capillary waves' polar angle difference between the two conditions reaches 10.44 . There is an obvious periodicity and damping attenuation mechanism in the oscillation process. In the droplet-fiber system, the oscillation process attenuates faster and the average oscillation period is shorter. The droplet relaxes to a stable state more quickly.

Experimental Analysis of Fundamental Water Droplet Coalescence Mechanisms on a Single Vertical Fiber

“…Even though based on the literature droplet bouncing should not occur we consider here the seen motion of droplet 5 to be based on droplet bouncing with droplet 13. The influence of the fiber on droplet bouncing remains uncertain but is expected to be neglectable when the droplet contact area is outside fiber like for the bridging process mentioned already by Zhang et al [24]. In Figure 16 it is clearly visible, that the fiber is off center of the contact area but no statement can be made as to whether the fiber is also outside the contact area.…”

“…If this is also valid for the coalescence of sessile droplets on a fiber than this could cause a chain reaction of coalescence events of closely spaced droplets on a fiber. Zhang et al [24] used two needles to position two droplets side by side on a horizontal fiber. According to their results, the influence of the fiber on the formation of the bridge can be neglected.…”

“…Further investigations of the coalescence process were conducted independently of filtration issues with droplets fixed to needles. This research mostly focuses on the initial process during coalescence, where a liquid bridge is formed between two droplets [24][25][26][27][28][29]. The bridging process is determined by the differing Laplace pressure and surface tension when two droplets come into contact due to jumpto-contact instability based on van der Waals forces.…”