Centrifugal creaming of concentrated oil-in-water emulsions: Experimental investigation and modelling

Abstract

This study investigates the creaming dynamics of concentrated oil-in-water emulsions. The variation of the concentration of the emulsion over both height and time is tracked using light transmission. Centrifugation forces are applied to accelerate the creaming rate, and so to permit studying relatively stable emulsions within shorter time frames. The packed layer is estimated to be denser when increasing the centrifugation force, and with bigger droplets as they are more likely to deform. The stability against creaming is found to be enhanced in several ways: increasing the dispersed phase fraction, decreasing the droplet diameter, decreasing the density difference between both phases or increasing the viscosity of the continuous phase. Interestingly, variable creaming rates are observed for droplets of different sizes within the same sample. This results in a packed layer with an increasing droplet size along its height. A convection-diffusion equation is employed to model the droplet displacement under centrifugal forces and to determine the dynamic local fractions. The model parameters were identified by fitting to the experimental data. The diffusion coefficient is found to be non-negligible in concentrated emulsions. Moreover, increasing the dispersed phase fraction hinders the velocity of droplets, which is accounted for in the model using a power parameter.