Taylor flow

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Modelling of mass transfer in Taylor flow: investigation with the PLIF-I technique

Modelling of mass transfer in Taylor flow: investigation with the PLIF-I technique

knowledge and understanding of the phenomena occurring at the local scale are still lacking, which could lead to pre-design rules and scaling laws for monolith reactors. In the present work, mass transfer is investigated at the bubble and slug scale in Taylor flow in a channel of 3 mm of internal diameter, by use of non-invasive techniques with high spatial and temporal resolutions: shadowgraphy and Pla- nar Laser Induced Fluorescence with dye Inhibition (here after PLIF-I). The objectives are (i) to measure dissolved gas concen- tration values in liquid phase, (ii) to compare them to existing mass transfer models in order to sort those of most relevance, (iii) to quantify lubrication film and bubble cap contributions in an attempt to understand the phenomena taking place, and (iv) to propose an improved model, allowing for the prediction of the dissolved oxygen concentration [O 2 ] in films and slugs along the channel. This model, based on phenomenological considerations, is intended as a method for fast and easy esti- mation of gas–liquid mass transfer for pre-design of monolith reactors.
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Hydrodynamics of gas-liquid Taylor flow in microchannels

Hydrodynamics of gas-liquid Taylor flow in microchannels

methods. A comparison of numerical methods comprising the transport scheme (VOF- FCT, VOF-PLIC and LS), the surface tension scheme (continuum or sharp surface force) and the curvature calculation (height function or divergence of the normal to the interface) with the same flow solver has been carried out. It can be concluded that the height function curvature calculation is very accurate and is particularly interesting for the case of static bubbles and near-static bubble or oscillating bubbles (Herrman [2008], Fuster et al. [2009]). However, since the errors generated during the advection step are captured while they are smoothed with the convolution method, the height function method needs to be coupled to an accurate transport scheme, as it has been shown with the translating and rotating cases in this study. Otherwise, the classic CSF formulation with a smoothing of the volume fraction gives better results in terms of maximum spurious currents intensity. Although, when using the Level Set formulation, the exact balance between pressure and capillary forces reached with the VOF-HFCSF methods is not achieved due to the redistancing step, it has been shown that the spu- rious currents are decreased in dynamic cases. Similarly to the VOF-HFCSF methods, the sharp surface force that interpolates the position of the interface and the height function technique require accurate transport and redistancing schemes since they also precisely capture the slight errors created in these steps. Finally, it is shown that these test cases are well adapted to the characterization of spurious currents in Taylor flow. The spurious currents generated in VOF-FCT simulations are shown to significantly modify the structure of the flow by producing an additional recirculation zone. The LS-CSF method is shown to be able to estimate the bubble slip velocity and the pres- sure drop across the bubble with good accuracy in a wide range of capillary numbers. In addition, since only one bubble is simulated, the global mass redistribution allows mass conservation problems to be avoided. However, cases involving several bubbles (or drops) still require additional work to resolve this mass conservation problem. Two possible solutions may be considered in future work: the improvement of the transport scheme in a VOF framework coupled to height function curvature calculation; and the coupling between VOF and LS methods (Sussman and Puckett [2000]). An other topic that should be considered for the simulation of Taylor flows is the (semi-)implicitation of the surface tension force (Raessi et al. [2009]).
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Bubble effect on the structures of weakly turbulent couette taylor flow

Bubble effect on the structures of weakly turbulent couette taylor flow

respectively) and a premature change in the second instability’s wave number. This non exhaustive overview shows the discrepancy with the previous results according to the regime of the Couette Taylor flow. This gives rise to the following questions: do the bubble induced effects depend on the bubble size and their localization in the gap rather than on the flow regime? To furnish some elements of response and complete a general background, experiments were conducted in a bubbly Couette Taylor flow for different bubble size and for unstudied flow regimes. Bubbles of different size are generated either by ventilation or by injection and pressure drop (gaseous- cavitation). Experiments were conducted at Ta=780 and Ta=1000, corresponding to quasi-periodic and weakly turbulent flows. In these conditions, what does the bubble arrangement looks like and are there any effects of the bubble on the flow patterns? Particular attention is paid to the transition between the two regimes studied. To have a good insight into the bubbly flow patterns, it is necessary to quantify locally the void fraction, bubble size and velocity. Consequently, a large experimental apparatus was especially built, in order to introduce optical probes. Detailed information about the liquid flow properties is given by LDV measurements and visualizations. To our knowledge, here are the first measurements of the dispersed phase characteristics achieved in a bubbly Couette Taylor flow.
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Hydrodynamics of gas-liquid Taylor flow in rectangular microchannels

Hydrodynamics of gas-liquid Taylor flow in rectangular microchannels

To cite this version : Abadie, Thomas and Aubin, Joelle and Legendre, Dominique and Xuereb, Catherine. Hydrodynamics of gas-liquid Taylor flow in rectangular microchannels. (2012) Microfluidics and Nanofluidics, vol. 12 (n° 1-4). pp. 355-369. ISSN 1613-4982

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Preferential accumulation of bubbles in Couette-Taylor flow patterns

Preferential accumulation of bubbles in Couette-Taylor flow patterns

When the inner cylinder rotates, the selection of the flow pattern is controlled by a centrifugal instability of the purely azimuthal Couette flow, and toroidal steady vortices 共Taylor vortex flow 兲 occur beyond a first threshold. While the Taylor number 共see Sec. II for definition兲 increases above the threshold of the second instability, the flow becomes time- dependent as vortices undergo wavy oscillations 共wavy vor- tex flow兲. Increasing further the Taylor number 共related to the nondimensional centrifugal forcing兲 induces a modula- tion of the wavy shape of the vortices; eventually turbulence sets in gradually. Bubbles injected in these various flow pat- terns have intricate responses. Early observations by Shiomi et al. 6 showed that bubble accumulation forms geometrical arrangements like rings and spirals. In these experiments, the axial volumetric fluxes of air and water were varied for dif- ferent rotation rates of the inner cylinder. The authors were able to summarize the numerous two-phase flow patterns in a configuration map, but the underlying physics remained un- clear. Later, Atkhen et al. 3 studied a highly turbulent Couette-Taylor flow with axial fluid flux. The flow was seeded with small air bubbles to make visualization of spiral vortices easy. The authors observed that bubbles collect at particular locations along the inner wall. More precisely, bubbles were attracted in outflow regions where the fluid flows radially from the inner cylinder toward the outer wall. Those locations correspond to low-pressure areas. The au- thors used bubbles as tracers of the traveling Taylor vortices. A precise understanding of the mutual interactions between the continuous fluid phase and the dispersed bubbles started with the experimental study of Djeridi et al. 2 These authors carried out a series of experiments based on the observation of bubble migration within Taylor vortices. A more compre- hensive inspection of arrangements of the dispersed phase together with flow structure modulations induced by bubbles was also presented by Djeridi et al. 1 Bubbles were condens- able 共generated by cavitation兲 or noncondensable 共originat- ing from free surface agitation 兲. Results were compared to simplified models providing a prediction of the average dis- tance between consecutive rings of bubbles. Modifications of the flow structure and instability thresholds were also reported.
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Hydrodynamics of gas-liquid Taylor flow in rectangular microchannels

Hydrodynamics of gas-liquid Taylor flow in rectangular microchannels

To cite this version : Abadie, Thomas and Aubin, Joelle and Legendre, Dominique and Xuereb, Catherine. Hydrodynamics of gas-liquid Taylor flow in rectangular microchannels. (2012) Microfluidics and Nanofluidics, vol. 12 (n° 1-4). pp. 355-369. ISSN 1613-4982

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Analysis of the flow pattern modifications in a bubbly Couette-Taylor flow

Analysis of the flow pattern modifications in a bubbly Couette-Taylor flow

Handle ID: . http://hdl.handle.net/10985/10301 To cite this version : Amine MEHEL, Céline GABILLET, Henda DJERIDI - Analysis of the flow pattern modifications in a bubbly Couette-Taylor flow - Physics of Fluids - Vol. 19, p.118101-1: 118101-4 - 2007

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Analysis of the flow pattern modifications in a bubbly Couette-Taylor flow

Analysis of the flow pattern modifications in a bubbly Couette-Taylor flow

Handle ID: . http://hdl.handle.net/10985/10301 To cite this version : Amine MEHEL, Céline GABILLET, Henda DJERIDI - Analysis of the flow pattern modifications in a bubbly Couette-Taylor flow - Physics of Fluids - Vol. 19, p.118101-1: 118101-4 - 2007

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Modelling of mass transfer in Taylor flow: investigation with the PLIF-I technique

Modelling of mass transfer in Taylor flow: investigation with the PLIF-I technique

knowledge and understanding of the phenomena occurring at the local scale are still lacking, which could lead to pre-design rules and scaling laws for monolith reactors. In the present work, mass transfer is investigated at the bubble and slug scale in Taylor flow in a channel of 3 mm of internal diameter, by use of non-invasive techniques with high spatial and temporal resolutions: shadowgraphy and Pla- nar Laser Induced Fluorescence with dye Inhibition (here after PLIF-I). The objectives are (i) to measure dissolved gas concen- tration values in liquid phase, (ii) to compare them to existing mass transfer models in order to sort those of most relevance, (iii) to quantify lubrication film and bubble cap contributions in an attempt to understand the phenomena taking place, and (iv) to propose an improved model, allowing for the prediction of the dissolved oxygen concentration [O 2 ] in films and slugs
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Mixing and recirculation characteristics of gas-liquid Taylor
flow in microreactors

Mixing and recirculation characteristics of gas-liquid Taylor flow in microreactors

be made non dimensional by dividing it by the time taken for the bubble to travel a distance equal to the slug length:  rc = t rc /(L S /U B ). In our previous work we have explored the effects of fluid properties, operating conditions and microchannel geometry on the size of Taylor bubbles ( Abadie et al., 2012 ) and the flow patterns in the liquid slug using micro Particle Image Velocimetry ( − PIV) ( Zaloha et al., 2012 ). The objective of this work is to explore the effects of operating parameters (capillary, Ca, and Reynolds numbers, Re) and microchannel aspect ratio (˛ = w/h = [1; 2.5; 4]) on the mixing and recircu- lation characteristics of the liquid slug in gas–liquid Taylor flow in microchannels. To do this, 3-dimensional VOF sim- ulations of gas–liquid Taylor flow in microchannels have been performed. Using an approach that is analogous to the determination of circulation rate in stirred tanks, the recirculation rate in the liquid slug, as well as the size of the recirculating zone have been evaluated from the 3- dimensional numerical data. An attempt has been made to relate these characteristics of the recirculating liquid slug to the enhanced transport phenomena observed in Taylor flow in microreactors. Finally, recommendations on the design and operation of microreactors employing Taylor flow are given.
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Two-phase Couette–Taylor flow: Arrangement of the dispersed phase and effects on the flow structures

Two-phase Couette–Taylor flow: Arrangement of the dispersed phase and effects on the flow structures

Handle ID: . http://hdl.handle.net/10985/10302 To cite this version : Henda DJERIDI, Céline GABILLET, Jean-Yves BILLARD - Two-phase Couette–Taylor flow: Arrangement of the dispersed phase and effects on the flow structures - Physics of Fluids - Vol. 16, n°1, p.128-139 - 2004

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Characteristics of liquids lugs in gas–liquid Taylor flow in microchannels

Characteristics of liquids lugs in gas–liquid Taylor flow in microchannels

be obtained, including bubbly flow, slug or Taylor flow, slug- annular flow, annular flow and churn flow. Amongst these, slug or Taylor flow occupies the largest region on the flow regime map and appears at low to average gas and liquid flow rates. The gas– liquid Taylor dispersion in microchannels is extremely regular and is characterized by bubbles separated by slugs of liquid. The bubbles occupy almost the entire channel cross-section and are separated from the channel wall by a thin liquid film. Taylor flow is considered as a promising flow regime for gas–liquid chemical reaction in microreactors for two reasons: it is generated over a large range of gas and liquid flow rates, making the process operating conditions very flexible; and the physical flow pattern provides high interfacial area and velocity fields that are extre- mely interesting for process intensification.
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Characteristics of liquids lugs in gas-liquid Taylor flow in microchannels

Characteristics of liquids lugs in gas-liquid Taylor flow in microchannels

Micro-PIV measurements have been performed in gas–liquid Taylor flow in microchannels to determine the effects of flow rates and channel geometry on the liquid velocity fields. Using the flow data and a method adapted from traditional batch mixing analysis, the recirculation motion in the liquid slug has been quantified by evaluating the recirculation rate, velocity and time. The measured velocity fields confirm the existence of circulation loops in the liquid slugs of gas–liquid Taylor flow in both straight and meandering microchannels. In the straight microchannel, the size of and the positions of the center of the recirculation loops are almost constant for the range of operating conditions investigated and they are symmetrical about the center line of the channel. In order to obtain recirculation patterns that demonstrate bypass flow with a reduced recirculation volume and vortex centers that are closer to the channel center line, the capillary number needs to be increased at least one or two orders of magnitude. This would typically require fluids with varying viscosity and/or surface tension to be used in the existing experimental setup. In meandering channels, the bends induce a highly three-dimensional flow that is non-symmetrical about the channel center line and dependent on the bubble position. A ‘liquid only’ zone (that is never occupied by bubbles) exists in the case of right-angled bend microchannels. This zone occupies about a third of the channel corner, however a quantitative analysis of the liquid in this area shows that the majority of the liquid in this area is in motion with fluctuating velocities. This enables us to conclude that the corner area in the microchannel is not entirely a dead zone and it is involved in heat and mass transport processes.
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Predicting inter-phase mass transfer for idealized taylor flow : a comparison of numerical frameworks

Predicting inter-phase mass transfer for idealized taylor flow : a comparison of numerical frameworks

Fig. 4 illustrates the different regions of the idealized Taylor flow pattern, and the general discretization strategy used within each region. Three grid resolution parameters were utilized to ensure consistency between each of the regions: Number of radial cells within the film region, N film,radial ; number of radial cells within the slug bulk, N bulk,radial ; and number of axial cells per channel diameter length, N axial , applicable to both the slug and bubble regions. The radial cell widths were determined such that the cross-section for flow was equivalent for each cell within a given region. Additional constraints were placed on the radial cells within the slug bulk, such that the forward flowing and backward flowing sub-regions contained an equal number of cells.
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Effect of bubble’s arrangement on the viscous torque in bubbly Taylor-Couette flow

Effect of bubble’s arrangement on the viscous torque in bubbly Taylor-Couette flow

persistent leading to an axial periodicity of the flow. A detailed characterization of the vortices is performed for the single-phase flow. The experiment also develops bubbles tracking in a meridian plane and viscous torque of the inner cylinder measurements. The findings of this study show evidence of the link between bubbles localisation, Taylor vortices, and viscous torque modifications. We also highlight two regimes of viscous torque modification and various types of bubbles arrangements, depending on their size and on the Reynolds number. Bubbles can have a sliding and wavering motion near the inner cylinder and be either captured by the Taylor vortices or by the outflow areas near the inner cylinder. For small buoyancy effect, bubbles are trapped, leading to an increase of the viscous torque. When buoyancy induced bubbles motion is increased by comparison to the coherent motion of the liquid, a decrease in the viscous torque is rather observed. The type of bubble arrangement is parameterized by the two dimensionless parameters C and H introduced by Climent et al. [“Preferential accumulation of bubbles in Couette-Taylor flow patterns,” Phys. Fluids 19, 083301 (2007)]. Phase diagrams summarizing the various types of bubbles arrangements, viscous torque modifications, and axial wavelength evolution are
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Effect of bubble’s arrangement on the viscous torque in bubbly Taylor- Couette flow

Effect of bubble’s arrangement on the viscous torque in bubbly Taylor- Couette flow

Keywords: bubble dispersion, viscous torque, Taylor vortices I. INTRODUCTION In the context of naval hydrodynamics, bubble injection in the turbulent boundary layer of ship’s hull appears as a promising solution to reduce the hull viscous resistance. However, despite several attempts in this field, the physical mechanisms implied into the bubbly drag reduction are to the best of our knowledge, not completely understood 1 . Consequently, it is still non straightforward to extrapolate results obtained for small scale models to large scale ship’s hull model. Moreover, a bubble injection system that is appropriate for a typical ship’s hull and a specific velocity range can be no more fitted when it is carried out for a different ship hull and/or other velocity ranges 2 . Therefore, there is still a need to develop theoretical research and applied experiments oriented to a better understanding of bubbly drag reduction.
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Experimental and numerical investigation on mixing and axial dispersion in Taylor-Couette flow patterns

Experimental and numerical investigation on mixing and axial dispersion in Taylor-Couette flow patterns

Rudman (1998) found that the Sc value reached an asymp- totic value of 0.155 as Re increases, indicating that in wavy vortex flow beyond a certain limit of the rotation speed the axial dispersion varies very weakly. However, our results show that the modulation of the wavy flow with additional frequen- cies (MWVF) can influence the dispersion significantly. The dispersion based Schmidt number can go below the asymp- totic value given by Rudman. This could be explained by the characteristics of this flow discussed earlier in Section 3.1 . The modulation increases the interactions between vortices which enhances axial dispersion and reduces Sc .
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Effect of bubble’s arrangement on the viscous torque in bubbly Taylor- Couette flow

Effect of bubble’s arrangement on the viscous torque in bubbly Taylor- Couette flow

IV. CONCLUSIONS The research developed in this paper explores and studies the interactions between the dispersion of the bubbles, coherent motion and viscous torque in a Taylor-Couette flow. Bubbles of diameter 0.05d to 0.125d (d being the gap width) were injected, for very small void fraction (α  0.23%). Two mixtures of water-glycerol were used, covering the ranges of Re numbers up to turbulent flow with persistence of the Taylor vortices. Several experimental techniques have been developed, a torquemeter was used to measure the global torque applied to the inner cylinder, while a video recording of bubble trajectories was used to determine the Eulerian distribution of the gas-phase in a meridian plane (void fraction distribution and gas- phase averaged axial and radial velocity distributions). In order to take into account the specificity of the Taylor-Couette configuration, a specific image processing procedure has been applied on bubble trajectories, to limit the depth of field and the contribution of azimuthal motion of the bubbles to the determination of apparent radial position and radial velocity component. Our study maps for the first time, the void fraction and the gas-phase averaged velocity in a bubbly Taylor-Couette flow.
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A photosynthetic rotating annular bioreactor (Taylor–Couette type flow) for phototrophic biofilm cultures

A photosynthetic rotating annular bioreactor (Taylor–Couette type flow) for phototrophic biofilm cultures

In their natural environment, the structure and functioning of microbial communities from river phototrophic biofilms are driven by biotic and abiotic factors. An understanding of the mechanisms that mediate the community structure, its dynamics and the biological succession processes during phototrophic biofilm development can be gained using laboratory-scale systems operating with controlled parameters. For this purpose, we present the design and description of a new prototype of a rotating annular bioreactor (RAB) (TayloreCouette type flow, liquid working volume of 5.04 L) specifically adapted for the cultivation and investigation of phototrophic biofilms. The innovation lies in the presence of a modular source of light inside of the system, with the biofilm colonization and development taking place on the stationary outer cylinder (onto 32 removable poly- ethylene plates). The biofilm cultures were investigated under controlled turbulent flowing conditions and nutrients were provided using a synthetic medium (tap water supple- mented with nitrate, phosphate and silica) to favour the biofilm growth. The hydrodynamic features of the water flow were characterized using a tracer method, showing behaviour corresponding to a completely mixed reactor. Shear stress forces on the surface of plates were also quantified by computer simulations and correlated with the rotational speed of the inner cylinder. Two phototrophic biofilm development experiments were performed for periods of 6.7 and 7 weeks with different inoculation procedures and illumination intensities. For both experiments, biofilm biomasses exhibited linear growth kinetics and produced 4.2 and 2.4 mg cm 2 of ash-free dry matter. Algal and bacterial community
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Experimental investigation of mixing and axial dispersion in Taylor–Couette flow patterns

Experimental investigation of mixing and axial dispersion in Taylor–Couette flow patterns

Abstract The flow and mixing in a Taylor–Couette device have been characterized by means of simultaneous particle image velocimetry and planar laser-induced fluorescence (PLIF) measurements. Concentration of a passive tracer measurements was used to investigate mixing efficiency for different flow patterns (from steady Taylor vortex flow to modulated wavy vortex flow, MWVF). Taylor–Couette flow is known to evolve toward turbulence through a sequence of flow instabilities. Macroscopic quantities, such as axial dis- persion and mixing index, are extremely sensitive to internal flow structures. PLIF measurements show clear evidences of different transport mechanisms including intravortex mixing and tracer fluxes through neighboring vortices. Under WVF and MWVF regimes, intravortex mixing is controlled by chaotic advection, due to the 3D nature of the flow, while intervortex transport occurs due to the presence of waves between neighboring vortices. The combination of these two mechanisms results in enhanced axial dispersion. We show that hysteresis may occur between consecutive regimes depending on flow history, and this may have a significant effect on mixing for a given Reynolds number.
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