**4. Conclusions**

Droplet formation in a two-pore membrane emulsification has been numerically investigated in this chapter. The dynamics of droplet formation has been investigated by solving the two-phase governing equations using VOF method. The effects of various parameters, viz., dispersed and continuous phase flow rate, surface tension and viscosities on the droplet dynamics have been investigated. The dynamics of evolution of dispersed phase and droplets formation show the dripping and jetting behavior depending upon the operating conditions and properties of two-phase liquids in the emulsification system. At constant continuous phase flow rate, the dripping phenomenon occurs at low dispersed phase velocity i.e. at low *We* number and transits towards jetting with the increase in dispersed phase flow rate. At constant continuous phase flow rate, with the increase in dispersed phase flow rate, the droplet size increases initially but decreases as the system transits towards jetting. At constant dispersed phase flow rate, with the increase in continuous phase flow rate, the droplet size decreases and also detachment time. Two ways of dripping to jetting transition have been observed, one with the increasing dispersed phase flow rate at constant continuous phase flow rate and other way is reducing the surface tension at constant dispersed phase flow rate. Both the transitions show different physical structures. The effect of inertia force has been observed the negligible for high value of surface tension and significant for lower surface tension value. The distance between the pore in continuous flow direction depends upon the operating parameters leading to dripping to jetting mode but the pore distance in transverse direction is not affected by the dripping or jetting behavior. Thus at higher value of *We* number, due to formation of the jetting and the droplet formation from the tip, the distance of 10 pore diameter between the pores is not sufficient to avoid the contact and coalescence of two neighboring droplets. The droplet size in the process scales with four main forces: drag forces imparted by the continuous phase, inertia force imparted by dispersed phase, surface tension force and the gravity force. In dripping mode inertial force of dispersed phase has negligible effect as the surface tension and drag force are dominant whereas in jetting mode inertial force of dispersed phase and surface tension force take part in the droplet formation. The evolving vortices are observed in the initial stage of dripping mode but it disappears in later stage. Three important factors must be considered in order to obtain a high production rate in membrane emulsification. (i) A proper combination of continuous phase, dispersed phase flow rate and surface tension so that droplet formation is made just before the starting of surface instability in jetting region. (ii) A proper distribution of pores so that coalescence of droplets does not occur during the droplet growth. (iii) The crossflow velocity must be high enough to provide a sufficient wall shear stress at the membrane surface to transport the drops away from the pore opening and, thus avoid the static hindrance and drop coalescence.
