Effect of a liquid dispersed phase on the wall flow structure in static mixer J. Legrand * , K. Hirech, A. Arhaliass Universite ´ de Nantes, CNRS, GEPEA, UMR6144, CRTT – BP 406, 44602 Saint-Nazaire Cedex, France Received 10 October 2004; received in revised form 12 February 2006 Abstract The effect of a liquid dispersed on the wall flow structure in static mixer is analyzed by using an electrochemical method. Both laminar and turbulent flows have been investigated. The axial wall velocity gradient and turbulent intensity have been studied along the static mixer in both flow regimes and for different dispersed phase concentrations. The spectral analysis of the wall velocity gradient fluctuations was analyzed in the turbulent regime. For volume fraction higher than 5%, the effect of the dispersed liquid phase is very important for all the studied parameters. The turbulence associated to the dispersed phase leads to an increase of the energy dissipation in the static mixer and also to a modification of energy dissipation mechanism. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Electrochemical method; Liquid–liquid dispersion; Spectral analysis; Static mixer; Turbulence; Wall shear rate 1. Introduction The effect of a fluid or solid dispersed phase on flow turbulence is due to different parameters: particle sizes, physicochemical properties of both phases, shift velocity, droplet deformation, breakage and coalescence phenomena, ... Yuan and Michaelides (1992) have summarized six mechanisms which contribute to modify turbulence characteristics in two-phase systems: • turbulent kinetic energy dissipation by the particles, • apparent viscosity increase due to the dispersed phase, • particle wake, • fluid mass-added to particles, • velocity gradients between particles, • deformation of dispersed phase. 0301-9322/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijmultiphaseflow.2006.02.002 * Corresponding author. Tel.: +33 240 17 26 33; fax: +33 240 17 26 18. E-mail address: jack.legrand@gepea.univ-nantes.fr (J. Legrand). International Journal of Multiphase Flow 32 (2006) 593–605 www.elsevier.com/locate/ijmulflow