(609b) CFD Simulations of a RDC-Column for Apparatus Design and Scale-up

Extraction columns have been subject of investigation for decades. The importance and applicability of Computational Fluid Dynamics (CFD) is constantly growing with increasing calculation power of computers. So far, the physical reality is still far too complex to be predicted without using a bunch of models and assumptions. However, single-phase and two-phase simulations can be used in order to predict design parameters like the axial dispersion coefficient or the bubble hold-up. The single-phase flow of a Rotating Disc Contactor (RDC) extraction column (DK = 150 mm) was investigated. By applying Particle Image Velocimetry (PIV), twelve different operation conditions were recorded while varying the speed of shaft rotation and the volume flow of the continuous phase. The qualitative flow pattern did not vary between different operation conditions and seemingly appears to be a function of geometric dimensions only. Single phase CFD simulations (Reynolds Stress Model and Enhanced Wall Treatment) showed highly accurate agreement with experiments while two phase simulations are still rather unreliable. In the present work, more emphasis is put on the single-phase flow with the aim of gaining new findings for apparatus scale-up. It has been observed that industrial size columns have a completely different hydrodynamic behavior compared with lab scale columns of less than 300 mm diameter. Due to the different geometric ratios, new eddies and regions of stagnation can form. Those effects lead to reduced separation efficiency and deviation from empirical correlations. By using the settings from validated simulations, larger geometries can be investigated. The intention of the current work is to find distinctive geometric dimensions (i.e. diameter, compartment height?) for which alteration of the qualitative flow pattern is expected and/or observed.