Phase-splitting features and polydispersity of droplet/slug flow split in a mini-T-junction: Effect of wall wettability

Abstract

This paper reports an experimental study of the steady-state and statistical phase-splitting features of droplet/slug flow split in a mini-T-junction with a hydraulic diameter of ∼ 1 mm. Water and silicone oil are selected as the working fluids. How the wall wettability affects the phase-splitting features of the mini-T-junction is studied carefully. The droplet sizes are subjected to image analysis to study the polydispersity of the mother and daughter droplets at the inlet and two arms of the T-junctions. The wettability features of the T-junction have significant effects on the droplet splitting modes. It is found that even splitting of the droplet flow is accompanied by blocking splitting, whereas uneven splitting is accompanied by non-blocking splitting or non-splitting. In a hydrophobic T-junction (water contact angle = 110°), the transition from blocking splitting to non-blocking splitting starts at a capillary number of less than 0.01 and with mother droplets that are longer than twice the channel width (Ldrop>2W), whereas the transition is suppressed in a hydrophilic T-junction (water contact angle = 48°). Correspondingly, the polydispersity level of the split daughter droplets in the hydrophobic T-junction is 19–37%, whereas it is much higher in the hydrophilic T-junction, varying from 43% to 74%. For flow with given values of Ca and Ldrop, the polydispersity level of the split daughter droplets is also highly dependent on the splitting ratio of the continuous flow, with even splitting happening at intermediate values of the splitting ratio (0.4–0.6).