Analysis of a new type of high pressure homogeniser. Part B. Study of droplet break-up and recoalescence phenomena

Calculation of the flow pattern in a new small homogenising valve design (Stansted, U.K.), able to reach operating pressure as high as 350 MPa, was investigated in the first part of this paper using a Computational Fluid Dynamics method. Numerical simulation results are used in the present paper to better understand the emulsification process in the Stansted high-pressure homogeniser. Deformation of drops is supposed to occur in the intense elongational flow caused by the restriction between the piston and the seat of the valve. Deformation may be mainly followed by drop disruption in the narrow valve gap. Break-up probably also occurred in the highly turbulent region, located just at the exit of the gap, and underlined by the numerical investigation. Cavitation and the rate of recoalescence, first assumed from numerical results, are determined thank to experimental methods. Intensities of both phenomena strongly increase with homogenising pressure. Final droplet size of model oil-in-water emulsions is then the result of equilibrium between droplet break-up and recoalescence, which strongly depends on operating pressure. (C) 2004 Elsevier Ltd. All rights reserved.