Laminar Flow in a RVF Dynamic Filtration Unit: Local Hydrodynamic Approach
Résumé
We intend to design a dynamic filtration module to treat highly viscous fluid and complex rheological behaviour fluid such as fermentation broth or food liquid. To this end an experimental study in laminar flow regime with a very viscous newtonian model fluid in a dynamic filtration module was undertaken in order to access local velocity fields. The final objective is to better understand local hydrodynamic effects not only on filtration peformance improvement but also on biological fluid degradation and especially on microorganisms. Our previous result of global hydrodynamic analysis should be strengthened by the determination of local variables (shear rate, velocity and pressure) that cannot be easily estimated in the RVF module. By using Particle Image Velocimetry (PIV), a powerful photographic flow-visualization technique, the instantaneous velocity fields can be measured and analyzed within the RVF.
In this study, we applied PIV to study laminar velocity fields at 6 different slices in a 3 mm gap between the membrane and the impeller, two feeding flowrates were taken into account to realize the influence of flowrate on the velocity fields for a given rotation speed of the impeller. As a result, we firstly introduced velocity fields by comparing snapshot and mean vector fields. Secondly, velocity profile in angular direction and z direction was presented. And finally, we calculated a core coefficient which is defined by a ratio of fluid velocity and impeller velocity, in order to realize the mechanical efficiency and compare to the literature.