Flow characteristics of liquid–liquid two-phase flow in cavity-type microchannels

A visual experimental method was used to analyze the liquid–liquid two-phase non-mixing flow in cavity-type microchannels with seven different structural configurations (cavity width, cavity height, and cavity spacing). Silicone oil was used as the dispersed phase, and distilled water containing 0.5 wt. % SDS (Sodium Dodecyl Sulfate) was used as the continuous phase. At the operating flow rates (qd = 1–9 ml/h, qc = 1–100 ml/h) in this paper, the dimensionless length range of the droplet is between 0.0441 and 5.434. The flow process of droplets with different lengths was analyzed in detail. It was found that the cavity structure generates flow patterns different from those in straight channels and can alter the flow patterns in the straight sections. The fluctuation of droplet length in the straight micro-channel sections was small, while in the cavity sections, it exhibited periodic oscillations. The amplitude and period of the droplet length oscillations increased as the flow rate (qc) decreased. The droplet expansion width increased with the flow rate (q) and decreased as the Capillary number (Cac) increased. When Cac was small or q was large, the droplet expansion width increased with the cavity width. When Cac was large or q was small, the effect of increasing cavity width on droplet expansion weakened. The different cavity spacings led to varying degrees of blockage, thereby affecting the droplet expansion width. The cavity height primarily influenced longer droplets. Based on multivariate regression analysis, an empirical correlation for predicting the dimensionless droplet length was established. The correlation prediction error is within ±20%, and the MAD and MRD are 8.4% and −0.14%, respectively.