HYDRODYNAMICAL INTERACTIONS BETWEEN PARTICLES AND LIQUID FLOWS IN BIOCHEMICAL APPLICATIONS

The interactions between a turbulent flow field and discrete particles have numerous applications in biochemical engineering. On the one han d, flows have a strong influence on the particle motion, from which co nsequences for heat and mass transfer, mixing or even damage to partic les are derived. On the other hand, the presence of the discontinuous (solid) phase is regarded as altering the turbulent field (two-way cou pling). At present, no fully explained mechanism of this turbulence al teration is offered in the literature. However, the two-way coupling c an no longer be considered when the particle concentration becomes suf ficiently high. The dominant mechanism affecting the flow is then the particle-particle interaction. Until now, no clear definition of a dem arcation between hydrodynamic (fluid-particle interaction) and viscous (particle-particle interaction) influences in liquid-solid or liquid- solid-gas systems has been given in the literature. In this paper we p resent first a description of the forces acting on a particle in a flo w and the most relevant parameters linked to the response of a particl e to turbulent stimulations. Some illustrations are given for common b iochemical applications. The second part is concerned with the action of the particles on the turbulence, the main trends observed and their significance in such applications being focused on. It is also demons trated here that the transition between the hydrodynamic and the visco us regimes is located between 20% and 30% in solid volume concentratio n.