Mixing and axial dispersion in Taylor–Couette flows: The effect of the flow regime

Abstract

The paper focuses on mixing properties of different Taylor-Couette flow regimes and their consequence on axial dispersion of a passive tracer. A joint approach, relying both on targeted experiments and numerical simulations, has been used to investigate the interaction between the flow characteristics and local or global properties of mixing. Hence, the flow and mixing have been characterized by means of flow visualization and simultaneous PIV (Particle Imaging Velocimetry) and PLIF (Planar Laser Induced Fluorescence) measurements, whereas the axial dispersion coefficient evolving along the successive flow states was investigated thanks to dye Residence Time Distribution measurements (RTD). The experimental results were complemented, for each flow pattern, by Direct Numerical Simulations (DNS), allowing access to 3D information. Both experimental and numerical results have been compared and confirmed the significant effect of the flow structure (axial wavelength of Taylor vortices and azimuthal wavenumber) on axial dispersion.

Experimental investigation of mixing efficiency in particle-laden Taylor–Couette flows

“…These results are consistent with previously reported experimental and numerical studies (Campero and Vigil 1997;Desmet et al 1996a, b;Kataoka et al 1975;Tam and Swinney 1987;Rudman 1998). Simultaneous particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) measurements (Nemri et al 2014(Nemri et al , 2016 were combined to highlight the enhanced chaotic advection in the mixing process for wavy regimes. The purpose of the present study is to measure the specific role of a dispersed phase on the progressive mixing of dye under similar flow conditions.…”

“…One possible method to address this, frequently implemented in bubbly flows, is to extract dynamic masks of the bubble interfaces from PIV measurements combining another shadowgraphic channel (Lindken and Merzkirch 2002;Dussol et al 2016). Instead, we propose to use a second PLIF channel (Bruchhausen et al 2005;Bouche et al 2013), dedicated only to the accurate detection of particles, while the first one is aimed at tracking the tracer for the mixing study, as in single-phase configuration (Nemri et al 2016).…”

Influence of Shear‐Thinning Rheology on the Mixing Dynamics in Taylor‐Couette Flow

“…and indicate that shear‐thinning fluids are associated with a concentration of vorticity along some vortex boundaries and a reduction in vorticity in the vortex core region, which is likely to lead to a further decrease in the mixing time in the fast‐mixing regions and a further increase in the mixing time in the slow regions. This will act to reduce the overall efficiency of intra‐vortex mixing in shear‐thinning fluids relative to the Newtonian case, for which almost all estimates of the mixing times of Taylor‐Couette reactors have been derived , , , .…”

“…However, it can also be applied in continuous processes by superimposing a weak axial flow, in which case the flow is referred to as Taylor‐Couette‐Poiseuille flow and inter‐vortex mixing is no longer a requirement . Intra‐vortex mixing is controlled by the velocity gradients within vortices that continuously stretch and deform fluid , and has been shown to increase with the Reynolds number and show a weak dependence on the wave state . Desmet et al argued that each vortex can be modeled as two separate zones, an inner zone at the vortex core and an outer zone near the vortex boundaries.…”

Flow Characteristics and Coherent Structures in a Centrifugal Blood Pump

“…With increasing rotation rate, instabilities occur, leading to the formation of toroidal vortical structures superimposed on the azimuthal flow, described both experimentally and theoretically in the 1920s by Taylor [26,27]. This set the basis for a research area that thereafter has attained great attention for a wide range of parameters (Reynolds and Taylor numbers) [28][29][30][31][32][33][34][35][36].…”