Taylor-Couette Flow Research Articles

Sustainable drag reduction in Taylor-Couette flow using riblet superhydrophobic surfaces

Superhydrophobic surfaces (SHSs) have been proven effective in reducing frictional drag force in various flow conditions. However, at high flow speeds, the air plastron on these surfaces collapses, leading to a decline in their effectiveness. In this study, we investigated the frictional drag forces of various SHSs and their combination with surface patterns across a wide range of flow conditions (5.00×102 < Re < 1.12×105) by using an facile coating method. Our experiments involved incorporating a superhydrophobic coating on the inner cylinder of a custom-made Taylor-Couette apparatus, integrated with a rheometer to measure torque applied on the inner rotor as a function of rotational speed. As part of our research, we calculate the effective slip length to assess the drag reduction performance of coatings, revealing an effective slip length of around 63 µm on a flat SHS. Furthermore, we explore the combined effect of superhydrophobic coatings and triangular-shaped riblets on drag reduction in Taylor-Couette flow, comparing the performance of these surfaces based on the riblet’s sharpness and the Reynolds number. Our experimental results show a reduction in measured torque of up to 24 % and 48 % on a V-grooved SHS in laminar and turbulent flow, respectively. Longevity tests confirm that the designed surfaces maintain their superhydrophobicity and drag reduction performance under turbulent flow conditions. Overall, this work introduces a passive drag reduction strategy through surface design, which substantially mitigates the frictional drag force and demonstrating considerable potential for enhanced performance and increased efficiency of Taylor-Couette systems.

Zr-Doped High-Voltage Spinel LiNi0.5Mn1.5O4 Manufactured via the Coprecipitation Method.

Lithium nickel manganese oxide (LiNi0.5Mn1.5O4, LNMO) provides an elevated operating potential of 4.7 V and a theoretical capacity of 147 mAh g-1, without the need for expensive cobalt. Zr-doped LNMO was synthesized using the coprecipitation technique with Couette-Taylor flow. FE-SEM images and TEM SAED patterns revealed that Zr-doped LNMO formed truncated octahedral structures with exposed (100) crystal facets. When compared to undoped LNMO, Zr-doped LNMO exhibited superior electrochemical performance. Electrochemical evaluations showed that Zr0.1-LNMO achieved 85.9% rate capability at 10 C, significantly outperforming the 69.1% of bare LNMO. In addition, Zr0.1-LNMO exhibited high stability, maintaining 76.8% of the discharge capacity even after 100 cycles.

Ethanol Production Using Zymomonas mobilis and In Situ Extraction in a Capillary Microreactor

The bacterium Zymomonas mobilis is investigated as a model organism for the cultivation and separation of ethanol as a product by in situ extraction in continuous flow microreactors. The considered microreactor is the Coiled Flow Inverter (CFI), which consists of a capillary coiled onto a support structure. Like other microreactors, the CFI benefits from a high surface-to-volume ratio, which enhances mass and heat transfer. Compared to many other microreactors, the CFI offers the advantage of operating without internal structures, which are often used to ensure good mixing. The simplicity of the design makes the CFI particularly suitable for biochemical applications as cells do not get stuck or damaged by internal structures. Despite this simplicity, good mixing is achieved through flow vortices caused by Taylor and Dean vortices. The reaction system consists of two phases, in which the aqueous phase carries the bacterium and an oleyl alcohol phase is used to extract the ethanol produced. Key parameters for evaluation are bacteria growth and the amount of ethanol produced by the microorganism. The results show the suitability of the CFI for microbial production of valuable compounds. A maximum ethanol concentration of 1.26 g L−1 was achieved for the experiment in the CFI. Overall, the cultivation in the CFI led to faster growth of Z. mobilis, resulting in 25% higher ethanol production than in conducted batch experiments.

Efficient adsorption of antibiotics using MXene nanosheet delaminated by Taylor vortex flow

MXenes are emerging as a promising class of two-dimensional (2D) adsorbents suitable for various environmental applications. The present study explores the use of Ti3C2Tx MXene nanosheet, delaminated by Taylor vortex flow (TVF), namely d-MXene-CT, as an efficient adsorbent for fluoroquinolones (FQs). The TVF induced in the gap between two coaxial cylinders of the Couette-Taylor reactor enhances the delamination process, yielding larger and thinner MXene nanosheets with a specific surface area 12 fold higher than that of nanosheets delaminated by turbulent eddy flow (TEF), namely d-MXene-MT in a conventional mixing tank (MT) reactor. As a result, the d-MXene-CT exhibited superior adsorption performance, with removal capacity for ciprofloxacin (CIP) of 349 mg/g and for levofloxacin (LEV) of 290.51 mg/g, representing 40 ∼ 60 % improvement over d-MXene-MT (249 mg/g for CIP and 180.22 mg/g for LEV). The adsorption process follows the pseudo-second-order kinetics model and fits the Langmuir isotherm, indicating the involvement of a monolayer chemisorption mechanism. Further investigation revealed that the removal of CIP and LEV was mainly driven by electrostatic attraction between oxygen functionality of MXene and protonated nitrogen group of FQs. The study highlights the potential of d-MXene-CT as a promising adsorbent for treating (FQs) from contaminant water.

Torque and heat transfer characteristics in Taylor–Couette turbulence with an axially grooved cylinder

To describe the aerodynamic and thermal effects in the flow between the slotted stator and rotor of electric motors, we have conducted direct and large eddy simulations using the lattice Boltzmann method. The flow between the stator and rotor is influenced by turbulence and Taylor–Couette (TC) vortices. Axial grooves (slots) are incorporated either on the stationary outer cylinder or the rotating inner cylinder. These groove shapes and numbers are designed based on the groove geometry of drive motors used in commercial electric vehicles. The radius ratio of the TC flow configuration in this study is 0.955, and the simulated bulk Reynolds numbers reach up to 21000 which corresponds to the Taylor number of Ta=4.63×108. The characteristics of torque and heat transfer are analysed by comparing cases with and without grooves. Regardless of the groove placement, it is suggested that while the grooved surface effects are not significant on torque and heat transfer performance at Taylor numbers Ta≤107, where Taylor vortices are still evident, the effects become pronounced at Ta≥108 as the flow transitions to the ultimate regime.

Characterizing and predicting the partial slip subjected to variable gradients of velocity and pressure in eccentric micro-scale Taylor–Couette flows

In the context of eccentric micro-scale Taylor–Couette flow, variations in localized flow scales result in a non-uniform fluid–solid interface slip state, distinct from the typically studied uniform slip velocity distribution. This study introduces a boundary condition definition method aimed at characterizing partial slip states, complemented by a coupled iterative analysis system tailored to address this complexity. Key contributions include the development of a method for calculating the limiting shear stress, which considers local velocity gradients and pressures. Validation demonstrates that the locally derived slip state aligns more closely with Knudsen number distributions of local flow scales compared to traditional uniform slip models, and exhibits greater consistency with experimentally measured pressure distributions. Additionally, the study reveals that eccentric Taylor–Couette flow, characterized by significant variations in local flow scales and strong self-induced pressure effects, leads to complex distributions of local pressure, velocity gradients, and differences in local slip velocities. Specifically, the non-uniform distribution of local pressure gradients due to eccentricity results in partial slip occurring predominantly on the rotor in regions with positive pressure gradients, and on the stator in regions with negative pressure gradients. Furthermore, the variation in gap height exerts a greater influence on local slip compared to rotational speed and eccentricity ratio. Under certain conditions influenced by pressure gradients, the slip velocity on the rotor may exceed its tangential speed.

Study on Turbulent Taylor-Couette Flow with High Reynolds Number and Large Radius Ratio in High-Speed Canned Motor Pump Internals

Abstract The Taylor-Couette flow, a prevalent flow pattern in fluid machinery. This study investigates turbulent Taylor-Couette flow within the internal flow of a shield pump through numerical simulations. The study encompasses a range of radius ratios (0.934 to 0.977) and inner cylinder frequencies (50 to 383 Hz). Our findings reveal a significant positive correlation between torque magnitude and radius ratio within the studied parameter range. Additionally, an exponential relationship between non-dimensional torque and Taylor number was identified through fitting. Moreover, the study elucidates that larger radius ratios lead to an earlier transition to the final turbulent region with increasing Taylor numbers. Furthermore, detailed analysis of the flow field vortex structure demonstrates the profound influence of radius ratio on the number of Taylor vortices.

Time periodic solutions for the 2D Euler equation near Taylor-Couette flow

Time periodic solutions for the 2D Euler equation near Taylor-Couette flow

Investigation on the effect of vertical baffle plate on droplet size distribution and mixing efficiency in Taylor Reactor

The Taylor reactor is a dynamic mixer based on the principles of Taylor vortex flow. However, traditional Taylor reactors feature smooth inner and outer cylinder surfaces, presenting challenges in achieving uniform mixing and efficient mass transfer. These limitations do not meet the requirements of modern chemical processes for highly efficient mixing equipment. This article introduces a novel Taylor reactor equipped with vertical baffle plates, designed to overcome these challenges. A comprehensive methodology combining CFD-PBM and experimental techniques was employed to investigate both droplet size distribution and mixing performance in the annular gap. Compared to traditional designs, the new device demonstrates significantly lower COV at 0.018 and Sauter mean diameter at 38.3 μm. Optimal mixing efficiency is achieved at rotating Reynolds number (Re) of 1.17 × 105 and inlet Reynolds number (Rei) of 2.65 × 103. Numerical simulation results suggest that vertical baffles effectively enhance liquid-liquid interactions including collision, interface contact, and droplet residence time within the annular gap. Moreover, increased turbulent stress in the flow field contributes to greater vorticity, turbulence intensity, and turbulent kinetic energy resulting in smaller droplet sizes and improved mixing efficiency. These findings provide a theoretical foundation for hydraulic structural optimization design as well as widespread application of Taylor reactors.

Instabilities and particle-induced patterns in co-rotating suspension Taylor–Couette flow

The first experimental results on pattern transitions in the co-rotation regime (i.e. the rotation ratio $\varOmega = \omega _o/\omega _i &gt; 0$ , where $\omega _i$ and $\omega _o$ are the angular speeds of the inner and outer cylinders, respectively) of the Taylor–Couette flow (TCF) are reported for a neutrally buoyant suspension of non-colloidal particles, up to a particle volume fraction of $\phi = 0.3$ . While the stationary Taylor vortex flow (TVF) is the primary bifurcating state in dilute suspensions ( $\phi \leq ~0.05$ ), the non-axisymmetric oscillatory states, such as the spiral vortex flow (SVF) and the ribbon (RIB), appear as primary bifurcations with increasing particle loading, with an overall de-stabilization of the primary bifurcating states (TVF/SVF/RIB) being found with increasing $\phi$ for all $\varOmega \geq ~0$ . At small co-rotations ( $\varOmega \sim 0$ ), the particles play the dual role of stabilization ( $\phi &lt; 0.1$ ) and destabilization ( $\phi \geq ~0.1$ ) on the secondary/tertiary oscillatory states. The distinctive features of the ‘particle-induced’ spiral vortices are identified and contrasted with those of the ‘fluid-induced’ spirals that operate in the counter-rotation regime.

Methods for the Viscous Loss Calculation and Thermal Analysis of Oil-Filled Motors: A Review

Oil-filled motors (OFMs) are widely used in deep-sea exploration and oil well extraction. During motor operation, the rotor stirs the oil in the air gap, causing viscous loss. Viscous loss affects the temperature distribution inside the motor. Accurately calculating the viscous loss and temperature rise in OFMs can provide a basis for optimizing the motor’s structural design. Motor structural parameters, including the rotor’s outer diameter, air gap, and slot opening, have a significant impact on viscous loss. The working conditions of OFMs, such as rotor speed and environmental temperature, also affect viscous loss. The viscosity of hydraulic oil is highly influenced by temperature, and changes in viscosity can lead to changes in viscous loss. These changes in viscous loss, in turn, alter the temperature distribution. Therefore, the coupling relationship between viscous loss and temperature must be considered. Additionally, when Taylor vortices occur in the fluid, the surface roughness of the rotor also has a significant influence on viscous loss. Currently, both domestic and international research on viscous loss and thermal analysis struggle to simultaneously consider the coupling of viscous loss and the temperature field, rotor surface roughness, and the effect of motor structure. This paper summarizes the methods used in recent years for studying viscous loss and thermal analysis, and puts forward some suggestions for future research on the coupling of the OFM temperature field and viscous loss.

Optimising Flywheel Energy Storage Systems: The Critical Role of Taylor–Couette Flow in Reducing Windage Losses and Enhancing Heat Transfer

Amidst the growing demand for efficient and sustainable energy storage solutions, Flywheel Energy Storage Systems (FESSs) have garnered attention for their potential to meet modern energy needs. This study uses Computational Fluid Dynamics (CFD) simulations to investigate and optimise the aerodynamic performance of FESSs. Key parameters such as radius ratio, aspect ratio, and rotational velocity were analysed to understand their impact on windage losses and heat transfer. This study reveals the critical role of Taylor–Couette flow on the aerodynamic performance of FESSs. The formation of Taylor vortices within the airgap was examined, demonstrating their effect on temperature distribution and overall system performance. Through a detailed examination of the skin friction coefficient and Nusselt number under different conditions, this study identified a nonlinear relationship between rotor temperature and rotational speed, highlighting the accelerated temperature rise at higher speeds. The findings indicate that optimising these parameters can significantly enhance the efficiency of FESSs, reducing windage losses and improving heat transfer. This research provides valuable insights into the aerodynamic and thermal optimisation of FESSs, offering pathways to improve their design and performance. The results contribute to advancing guidelines for the effective implementation of FESSs in the energy sector, promoting more sustainable energy storage solutions.

On particle-modified velocity fields of particulate Taylor–Couette flow

Particulate Taylor–Couette flow of a particle-laden viscous fluid between two coaxial rotating cylinders is studied using a novel hydrodynamic model. With the volume fraction of particles as the dimensionless small parameter, explicit leading-order solutions are derived for the general case of dispersed particles heavier or lighter than the carrier fluid. It is shown that, unlike the classical azimuthal velocity field of a clear fluid without particles, dispersed particles generally have a radial velocity toward the outer or inner cylinder depending on the angular velocities and radii of the two cylinders and whether the particles are heavier or lighter than the carrier fluid, in qualitative agreement with some known results reported in literature on heavier or lighter particles, respectively. In some cases, such as the flow driven by rotating inner cylinder with a wider gap between the two cylinders and a moderate value of Stokes number of particles, our results predict the existence of a circular ring between two cylinders, which attracts or repels heavier or lighter particles that could have relevant physical implications. Beyond existing literature on the Taylor–Couette flow with neutrally buoyant particles, these results could offer new insight and useful explicit solutions to the Taylor–Couette flow with particles heavier or lighter than the carrier fluid.

Modeling of nonequilibrium effects in a compressible plasma based on the lattice Boltzmann method

A magnetohydrodynamic lattice Boltzmann method (MHD-LBM) model for a 2D compressible plasma based on the finite volume scheme is established. The double distribution D2Q17 discrete velocities are used to simulate the fluid field. The hyperbolic Maxwell equations, which satisfy the elliptic constraints of Maxwell's equations and the constraint of charge conservation, are used to simulate the electromagnetic field. The flow field and electromagnetic field are coupled to simulate a compressible plasma through the electromagnetic force and magnetic induction equations. Four typical cases, the Taylor vortex flow, strong blast, Orszag–Tang vortex, and one-dimensional Riemann problems, are simulated to validate the MHD-LBM model for a compressible plasma. It is found that shock waves widely exist in a compressible plasma, and strong nonequilibrium effects exist around each shock wave. The quantitative simulation for the Brio–Wu problem demonstrates that this model can easily obtain the physical characteristics of nonequilibrium effects at sharp interfaces (shock waves and detonation waves). The magnetic fields can affect the magnitudes to which the system deviates from its equilibrium state. The viscosity can increase the magnitudes to which the system deviates from its equilibrium state. Compared with existing compressible MHD, these results for nonequilibrium effects can provide mesoscopic physical insights into the flow mechanism of a shock wave in a supersonic plasma.

Bridging the Gap: Scaling up Processes for the Development of Li-Rich Mn-Rich Layered Oxides

As the global demand for more powerful and long-lasting energy storage solutions continues to grow, Li-rich Mn-rich layered oxides (LMR) emerges as a promising class of next-generation cathode materials for lithium-ion batteries. The LMR material stands out due to its impressive electrochemical specific capacity, surpassing 280 mAh g–1, along with a high discharge voltage exceeding 3.5 V. It also boasts a remarkable specific energy density close to 1000 Wh kg–1, all while maintaining a relatively lower cost.Current synthesis methods often rely on batch coprecipitation reactions followed by the calcination of precipitated Mn-rich precursors. However, the inherent challenges of batch reactions, particularly in terms of reproducibility and quality, prompt the exploration of more sophisticated approaches. Moreover, the transition from benchtop experiments to large-scale production introduces a distinct set of challenges. Parameters that work seamlessly on a smaller scale may not translate as effectively when producing the material at the kilogram scale. This scaling-up process involves navigating complexities such as chemical handling risks, and challenges related to reaction heat transfer and mixing efficiency. These factors collectively underscore the difficulties in achieving precise control over critical precursor characteristics, including primary and secondary particle size, morphology, tap density, and stoichiometry.In response to these challenges, this presentation will discuss an innovative approach. High-quality Li-rich Mn-rich materials are synthesized using continuous coprecipitation, facilitated by a pre-pilot scale Taylor Vortex Reactor (TVR) at the Materials Engineering Research Facility (MERF) in Argonne National Lab (ANL). This emerging synthesis technology offers a scalable solution for the production of high-quality cathode materials. This presentation will delve into the intricacies of the synthesis process, providing valuable insights into the relationship between the characteristics of the synthesized LMR precursors and their subsequent impact on cathode performance.

Cobalt recovery from spent lithium-ion batteries using a rotating cylindrical electrode reactor

Abstract The cobalt electrodeposition from a leaching containing cathode-powdery of spent laptop lithium-ion batteries (LIBs) of different commercial brands, collected from local laptop repair shops, was investigated. Citric acid (0.14 M) and hydrazine (0.1 M) were employed as complexing and reducing agents in the leaching during 24 h. Cobalt, manganese and nickel concentrations in the leachate, obtained by the flame method in an atomic absorption spectrometer, are reported. A rotating cylindrical electrode reactor which consists of a rotating open bottom as cathode and a static outer cylindrical as anode was employed. The numerical flow patterns and cathode velocities that induce the presence of Taylor vortices inside and/or outside the cathode were investigated. RANS equations with the standard k−ε turbulence model and enhanced wall treatment was used. Electrical power measurements were performed to validate simulations. Cyclic voltammetry experiments with synthetic solutions were applied to determine the reduction potential of cobalt (found in −1.2 V vs SCE). Subsequently, electrolysis experiments were carried out at predetermined cathode speeds (50, 75, and 125 rpm), imposing a working cathodic potential of −1.2 V versus SCE during 12 h. Experimental results indicate that the best cobalt recovery rates and current efficiency coincide with the presence of Taylor vortices both inside and outside the cathode, i.e., at 50 rpm. The peak performance in cobalt recovery and current efficiency was recorded at 49 % and 47.3 %, respectively. Finally, the deposits obtained from each electrolysis test were removed from the cathode and analyzed via energy dispersive spectroscopy. The range of purity of Co obtained in the electrodeposit film were between 56.75 % and 74.8 %.

Deracemization of sodium chlorate by hydrodynamic attrition of Taylor vortex flow

We investigated the deracemization of sodium chlorate in the unique hydrodynamic environment of Taylor vortex flow (TVF) in Couette-Taylor (CT) crystallizer. Our findings revealed a remarkable enhancement in the deracemization due to the effective hydrodynamic attrition of crystals, as compared to conventional mixing tank (MT) crystallizers utilizing the turbulent eddy flow (TEF). So, the deracemization of initial ee = 0 % in the CT crystallizer was significantly enhanced as increasing the rotation speed whereas the deracemization in the MT crystallizer occurred seldom with increase of agitation speed. Using the sparsely soluble solvent, it was demonstrated the TVF was much more effective for the hydrodynamic attrition of the crystals than the TEF. The deracemization depended not only on the flow intensity (viscous energy dissipation) but also the flow pattern. So, the TVF always produced the higher deracemization than the TEF at the same viscous energy dissipation. Also, the flow intensity and flow pattern significantly dictated the crystal agglomeration of homo-chiral (L-form and D-form) and hetero-chiral (L/D-form) forms during the deracemization. Our findings demonstrated the potential of the periodic TVF in the deracemization. The hydrodynamic attrition effect in the CT crystallizer provides a means to enhance enantiomeric purity and offers insights into the design of novel deracemization systems.

Elastically modulated wavy vortex flow

We investigate the transition pathway of low elasticity fluids (El=0.003−0.008) in a Taylor-Couette configuration using low-molecular-weight polyacrylamide (PAAM) and visualisation experiments in the Reynolds range from 0 to 300. We report here for the first time an elastically modified wavy vortex flow state with altered spectral and structural characteristics, that precedes the onset of the traditional (inelastic) Newtonian wavy instability. This new wavy regime is characterised by oscillations of both the inflow and outflow boundaries, associated with a weakening of the outflow regions due to low hoop stresses. The modification of the boundaries persists at higher Reynolds numbers, where the spectral characteristics are unaltered compared to the inelastic, Newtonian case. In addition, a hysteretic behaviour is observed for increasing elasticity, as instabilities are shifted towards lower critical Reynolds numbers, confirming the importance of even vanishing elasticity on the stability of Taylor-Couette flows. At higher fluid elasticity (El=0.06), the amplitude of inflows/outflows oscillations increases, and momentum is transferred axially between adjacent vortices, which may contribute to the emergence of Rotating Standing Waves.

Numerical simulation of evolution pattern of vortices in Taylor–Couette flow with three-lobe multiwedge clearance

Numerical simulation of evolution pattern of vortices in Taylor–Couette flow with three-lobe multiwedge clearance

High-order meshless global stability analysis of Taylor–Couette flows in complex domains

High-order meshless global stability analysis of Taylor–Couette flows in complex domains