Author(s)

T. Krebs, C. P. G. H. Schroen & R. M. Boom

Abstract

We present the results of experiments studying droplet coalescence in a dense layer of emulsion droplets using microfluidic circuits. The microfluidic structure allows direct observation of shear-induced collisions and coalescence events between oil droplets dispersed in water. A mineral oil was chosen as the dispersed phase and a 9 wt% NaCl aqueous solution as the continuous phase. We determine the coalescence rate as a function of the droplet velocity and droplet concentration from image sequences measured with a high-speed camera. A trajectory analysis of colliding droplet pairs allows evaluation of the film drainage profile and coalescence time tc. From the coalescence times obtained for ten thousands of droplet pairs we calculate the coalescence time distributions for each set of experimental parameters, which are the mean droplet approach velocity
v0  and the mean dispersed phase fraction
φ . We discuss the potential of the procedure for the prediction of emulsion stability in industrial applications. Keywords: emulsion, microfluidic, coalescence, kinetics, image analysis, droplet, film drainage, petroleum. 1 Introduction The control of emulsion stability is an important issue in many industrial applications. Our motivation is rooted in the field of crude-oil/water separation which is a key processing step in oil production. In this application, a common way to separate the liquid mixture is by using mechanical devices [1], like gravity settlers, centrifugal separators such as hydrocyclones or in-line swirl elements [2]. A criterion for the successful operation of these separators is

Keywords

emulsion, microfluidic, coalescence, kinetics, image analysis, droplet, film drainage, petroleum.