Behavior of Droplet Trapping in an L-Shaped Constricted Microchannel

The droplet trapping dynamics in an L-shaped constricted microchannel are investigated using three-dimensional numerical simulations and theoretical analysis. The observed droplet regimes include trapping and squeezing. Based on the theoretical balance of the hydrostatic pressure of flow exerted on the droplet and the net Laplace pressure of the droplet generated by contraction when entering the constricted microchannel, a theoretical model is proposed to predict the critical capillary number Ca governing the transition between the two regimes. The theoretical model considers the effects of the viscosity ratio \(\lambda \) and microchannel geometry, including the width ratio \({{C}_{I}}\) and the contraction ratio \({{C}_{{II}}}\). The results from the predictive equation closely match the numerical simulations, confirming the model’s accuracy. The study also explains how geometry, flow, and fluid properties affect the droplet behavior in constricted microchannels at low Reynolds numbers. It offers insights into controlling droplet trapping and release for biomedical and chemical applications, and serves as a useful reference for designing the microfluidic systems.