Droplet formation and its mechanism in a microchannel in the presence of an electric field

The instability of the interface between two immiscible Newtonian liquids in a microchannel in the presence of an electric field and the resulting micro droplets are experimentally investigated. In the experiments, ethylene glycol and silicone oil of different viscosities are pumped into a PMMA microchannel and a DC field is applied normal to the flat interface between the liquids. The effect of the viscosity ratio, the thickness ratio and the total flow rate, on the critical voltage, V-c at which the interface starts to deflect is investigated. An empirical formula is developed to relate the dimensionless critical electric number, E-b,E-c, to the thickness ratio, H-r and the viscosity ratio, mu(r). It is found that the thickness ratio is more important than the viscosity ratio. In the second part of the work, the evolution of the interface is studied and the droplet formation mechanism due to the electric field is presented in detail. The droplet size is investigated in terms of the thickness and viscosity ratios, and the total flow rate. An empirical formula for the droplet size is obtained as a function of the electric number, E-b the total flow rate, Q, the thickness ratio, H-r and the viscosity ratio, mu(r). It is possible to get smaller droplets with higher electric number, viscosity ratio, and total flow rate and smaller thickness ratio.