The falling, necking, and break-up of droplet between horizontal tubes with low Reynolds number

Abstract

Experimental observations and measurements concerning falling, necking, and break-up characteristics of a single droplet from a horizontal tube to the adjacent tube are performed using a high-speed digital camera. The droplet flow with a low Reynolds number at several tube-spacing are adopted in experiments. The morphological changes of droplet flow are presented in detail. With the increase of tube spacing, the droplet flow states of undeveloped droplet flow, pendant droplet flow, and complete droplet flow are presented successively between tubes. In addition, quantitative analyses about the necking process under different flow rates and tube diameters are discussed. The results show that the necking process can be divided into a linear necking region and a exponential necking region. In the linear necking region, the tube diameter has minor effect on the necking process, but the increase of flow rate makes the linear necking duration longer. In the exponential necking region, the initial conditions, such as tube diameter and flow rate, have no significant effect on the necking process. Moreover, the formation and evolution of satellite droplets are discussed in detail. For the complete droplet flow, the overhanging column breaks into several satellite droplets. The volume together with surface area of the detached droplet and satellite droplets are measured as well. The results show that the detached droplet plays a major role in the droplet flow, carrying most of liquid in the falling droplet. The effect of satellite droplets is mainly reflected in the first and second satellite droplets.