An experimental study on the stability of the interface between immiscible liquids in a micro channel subject to an electric field

Abstract

Micro channels offer many advantages for both industrial and laboratory applications. They provide the use of small amounts of sample, reduced cost and faster analysis. The flow regime is laminar in micro channels. Electrohydrodynamic (EHD) instability can be used in micro channels to obtain an efficient mixing for miscible liquids and to generate mono dispersed droplets for immiscible liquids. In this study, the purpose is to experimentally destabilize the flat interface between two immiscible and Newtonian liquids flowing in a rectangular micro channel in the presence of an electric field. The channels are of depth 0.2 mm and width 1.0 and 1.5 mm. The liquids are pumped into the micro channel with a syringe pump and a DC electric field is applied either parallel or normal to the flat interface formed between these immiscible liquids. The liquid pairs used in the experiments are a combination of ethylene glycol, silicone oils with different viscosities, castor oil, and olive oil. Electrohydrodynamic instability is investigated for several parameters including the ratios of viscosities and flow rates, the width of the micro channel and the direction of the electric field. The results of the experiments show that an increase in viscosity and flow rate ratios of silicone oil to ethylene glycol has a stabilizing effect in the presence of a normal electric field. In addition, it is found that only the ratio of the flow rates has an effect on the stability of the interface, not the individual flow rates of the liquids. Furthermore, an increase in the width of the channel results in an increase in the critical potential difference of the system. The range of voltages needed to destabilize the interface in the performed experiments are in between 94 and 1090 volts. Finally, it is shown that the parallel electric field does not have a destabilizing effect on the liquid pairs used in the study.