Dynamic Evolution of Drop in Immiscible Liquid-Liquid Systems at Low Flow Rate.

摘要

The mechanisms of drop formation in immiscible liquid-liquid systems are very important considering the aspects of drop on demand in chemical process industries, emulsification, mixing, extraction etc. The present work describes the theoretical model to predict the drop dynamics from a submerged nozzle. The resorted semi-analytical and numerical techniques are able to predict the drop shape as the liquid is injected from the submerged nozzle in immiscible environment. The static formation of liquid drops emanating from a submerged nozzle was analysed based on the principles of force balance. In the case of very small flow-rates and constant flow conditions, the formation takes place in a quasi- static manner and can thus be described by the Laplace equation as an equilibrium of surface, pressure and gravitational forces acting on the drop surface. The resulting ordinary differential equation then solved numerically to obtain the drop characteristics such as shape, volume, and height and pressure variations at the nozzle tip up to the limit of critical equilibrium of resistive and disruptive forces. At this stage the drop reaches its maximum volume and will inevitably disintegrate from the nozzle tip when further flow is added or if any small perturbation is applied. Experiments are performed with cyclohexane as dispersed phase and deionized water as quiescent fluid as shown in the figure. The sequence of cyclohexane drop formation with a flow rate of 1.5 ml/min at time 0.121, 0.449, 0.91 and 1.22 sec are compared with theoretical model. The comparison with the experimental results was found in good agreement.