Local hydrodynamic investigation by PIV and CFD within a Dynamic filtration unit under laminar flow

Abstract

To better understand the hydrodynamics in a Dynamic Filtration module (DF), a local investigation within a complex and confined module named Rotating and Vibrating Filtration (RVF) was scrutinized under laminar flow with viscous Newtonian fluid (Remixing = 45). RVF consists of two filtration cells in series, in which a three-blade impeller rotates between two membranes. Particle Image Velocimetry (PIV) measurements were conducted in different operating conditions and synchronized with an optical trigger. In parallel, a simulation approach by Computational Fluid Dynamics (CFD) was developed and compared to PIV. On one hand, PIV measurements indicated that velocity fields and profiles were highly organized and stable within the filtration cell, and mainly governed by the impeller shape. Different feeding flowrate had no significant influence on velocity profile. Considering velocity magnitude, the angular velocity was the dominant contribution compared to radial velocity. However, a particular oscillation of radial velocity component was demonstrated. On the other hand, CFD simulation was in good agreement with PIV regarding on velocity fields and profiles. Results showed that maximum velocity and shear stress appeared at the leading edge of the impeller. A dead-zone (around the surrounding wall of the filtration cell) and a short-cut (close to the central shaft) were confirmed by CFD streamlines under different operating conditions. Moreover, velocity coefficient of the RVF module was 0.31 (mean value) from PIV while 0.35 from CFD, and it was compared to the similar devices in the literature.