Theoretical analysis of 3D emulsion droplet generation by a device using coaxial glass tubes

In the present paper, we propose a theoretical analysis approach to the generation of monodisperse emulsion droplets by a device using coaxially fixed pulled glass tubes. Using this device, the dispersed phase fed into the inner glass tube forms a fluidic droplet and grows at the tube end due to surface tension before detaching due to the drag force applied by the continuous phase, which flows between the inner tube and the outer tube, as illustrated in Fig. 1. We established a theoretical model for this phenomenon and analyzed the forces applied to the fluidic droplet that is about to detach and obtained equations describing the relation among the droplet size, flow rate, and viscosity μ of the continuous phase, the sizes of the glass tubes, and the surface tension coefficient γ of the dispersed phase. Experiments were conducted under a variety of conditions in order to verify these equations. The experimental results agreed with the theoretical model with a low difference of less than 5%.