Three-dimensional simulation of dripping and jetting phenomenon in a flow-focusing geometry

Abstract

3D simulations have been achieved on a flow-focusing geometry employing the VOF method to study the consequence of viscosity, surface tension, wettability, and geometry on drop generation for the dripping regime. Here the dispersed phase is the PDMS oil (polydimethylsiloxane), and the continuous phase is the water. Simulations were performed at different oil-to-water viscosity ratios $\left(\frac{{\mu }_o}{{\mu }_w}\right)$ of 3, 12, 27, and 50. The interfacial tension between PDMS oil and water is 0.0118 N/m. It has been abridged to 0.008 N/m, 0.005 N/m, and 0.002 N/m, and simulations were performed. The walls of the microchannel are considered to be PMMA surfaces. The contact angle of an oil droplet on the PMMA surface in the presence of water is 140°. The effect of wettability was shown at various contact angles (angle created by water droplet on the PMMA surface in the presence of oil) of 0°, 40°, 90°, 135° and 180°. The frequency of droplet generation (1/s), non-dimensional droplet length (L/W_c), droplet volume (nl), and droplet velocity (m/s) have been calculated for each of the cases. A flow pattern map has been industrialized classifying the dripping and jetting regimes. A comparison between normal geometry and two constricted geometries (having different orifice lengths) based on the frequency of droplet, non-dimensional drop length, drop volume, and drop velocity has been made for both dripping and jetting regimes. Prediction of simulated non-dimensional droplet length has also been made using dimensional analysis.