Dynamics of pinch-off in liquid/liquid jets with surface tension

Full two-dimensional velocity fields were measured by PIV in forced jets of glycerin/water solution flowing into and pinching off in ambients of Dow Corning 200 Series silicone fluid. The Reynolds, Froude, and Bond numbers computed at the nozzle exit were 34, 0.20, and 6.1, respectively. Viscosity ratios between the inner and outer fluids of 0.17 and 1.7 were examined in jets forced at a Strouhal number of 4.0. The experiments revealed that the viscosity ratio strongly affected the evolving jet flow, the pinch-off process, and the resulting droplet shapes. The higher viscosity ambient yielded less gravitational acceleration within the jet fluid, a broader cone shape upstream and a more rounded drop interface downstream of the pinch-off zone, and eventually spheroidal droplets with weak oscillations in shape. The lower viscosity ambient yielded greater gravitational acceleration within the jet, a narrower cone shape upstream and flatter drop interface downstream of the pinch-off zone, and eventually strong oscillations including inverted curvature within the droplets that formed. The difference in downstream interface angles at pinch off could be explained by the velocity and vorticity distributions within the two flows.