Couette Device Research Articles

Design Considerations and Flow Characteristics for Couette-Type Blood-Shear Devices

Cardiovascular prosthetic devices, stents, prosthetic valves, heart-assist pumps, etc., operate in a wide regime of flows characterized by fluid dynamic flow structures, laminar and turbulent flows, unsteady flow patterns, vortices, and other flow disturbances. These flow disturbances cause shear stress, hemolysis, platelet activation, thrombosis, and other types of blood trauma, leading to neointimal hyperplasia, neoatherosclerosis, pannus overgrowth, etc. Couette-type blood-shearing devices are used to simulate and then clinically measure blood trauma, after which the results can be used to assist in the design of the cardiovascular prosthetic devices. However, previous designs for such blood-shearing devices do not cover the whole range of flow shear, Reynolds numbers, and Taylor numbers characteristic of all types of implanted cardiovascular prosthetic devices, limiting the general applicability of clinical data obtained by tests using different blood-shearing devices. This paper presents the key fluid dynamic parameters that must be met. Based on this, Couette device geometric parameters such as diameter, gap, flow rate, shear stress, and temperature are carefully selected to ensure that the device’s Reynolds numbers, Taylor number, operating temperature, and shear stress in the gap fully represent the flow characteristics across the operating range of all types of cardiovascular prosthetic devices. The outcome is that the numerical data obtained from the presented device can be related to all such prosthetic devices and all flow conditions, making the results obtained with such shearing devices widely applicable across the field. Numerical simulations illustrate that the types of flow patterns generated in the blood-shearing device meet the above criteria.

Experimental and mechanism study on wax deposit dissolution characteristics by light crude oil

During the sequential transportation of waxy crude oil and light oil, the previous formed wax deposits on the pipe wall will dissolve by light oil, which brings risks to the flow safety of the pipeline. This paper adopted a Couette wax deposit dissolution experimental device to systematically study the effects of dissolution duration, oil temperature, rotation speed and wax deposit properties on the dissolution characteristics of wax deposits. It is found that the dissolution of wax deposits is a process that starts quickly and then slows down. Moreover, the wax content of wax deposit also decreased during the dissolution process. The wax deposit dissolution process is mainly divided into five stages such as diffusion of wax molecules from wax deposit to the light oil and from bottom layer deposit to the wax deposit-oil interface, dissolution of wax crystal particles, weakening of wax deposit structural strength, and shear stripping of wax deposits. Finally, an empirical model of wax deposit dissolution was established and the undetermined parameters were fitted based on experimental data. The prediction results have good prediction accuracy with the experimental values.

Growth of Floc Structure and Subsequence Compaction into Smaller Granules through Breakup and Rearrangement of Aluminum Flocs in a Constant Laminar Shear Flow.

We have constructed an outer-cylinder-rotating Couette device for high-speed shear flow in laminar flow conditions and visualized the structure formation and subsequent rearrangement of PACl (flocculant made of aluminum hydroxide gel) and kaolinite flocs by visible light imaging. In a previous report, we analyzed the case of relatively low shear rate (G-value = 29 1/s) and confirmed that the flocculation process could be separated into two stages: a floc growth stage and a breakup/rearrangement stage. Once the large bulky flocs that reached the maximum size appeared, they rearranged and densified through structural fracture and rearrangement. In this report, this process was further investigated by conducting experiments under two different high shear rates (58 and 78 1/s) at which breakup and rearrangement became more pronounced, and three different aluminum kaolinite ratios (ALT ratios) that were over and under the optimum dosage (neutralization point by Zeta potential). Visualization results confirmed that, during the growth stage, the flocculation rate could be approximated by a scaling relationship between floc size and elapsed time, which depended on the ALT ratio. After reaching the maximum size, the floc rapidly became compact and dense following adsorption of the gel, incorporating fine fragments from erosion breakup. The over and under dosages created a lot of fragments of erosion breakup, but less so in the optimum dosage. In the optimum ALT ratio, fragments did not remain because they were incorporated into the flocs and densified, and the floc size was thought to be maintained. The floc circularity distribution peaked at around 0.6 and 1, suggesting that the flocs were spherical in shape due to erosion breakup.

Cohesive bond strength of marine aggregates and its role in fragmentation

Marine aggregates are one of the main contributors to carbon sequestration in the deep sea through the gravitational settling of biogenic particles formed from the photosynthetic products of phytoplankton. The formation of large particles due to aggregation processes has been the focus of studies in the past, but recent findings on the spatio-temporal distribution of particles suggests that the fragmentation of aggregates plays an important role in aggregate dynamics. Here, we assessed the yield strength of aggregates derived from natural planktonic communities in order to analyze the cohesive bond strength and further understand fragmentation. The experimental approach was designed around the use of a Couette device, which produces a constant laminar shear flow of water. Aggregates were found to have a higher yield strength (~289 ± 64 nN) during phases of nutrient depletion than those of mineral particles such as montmorillonite. Based on an estimated cohesive bond strength of 96 nN a numerical model to predict the temporal variation of aggregate size was created. The output of this model indicates that cohesive bond strength is a major determinant of the size of aggregates in motion. Our findings suggest that the dynamics of marine aggregates are greatly influenced by cohesive bond strength and the role in fragmentation.

The Effect of Temperature on the Size and the Deposition of Asphaltene Particles

Summary The deposition of asphaltene as a main component of crude oil is considerably affected by temperature. Despite the studies on influencing factors on deposition and size of asphaltene particles, no experimental research was previously conducted on the simultaneous impact of temperature on asphaltene particle size and deposition. In this study, the asphaltene deposit mass was measured within a Couette device at various temperatures ranging between 20 and 65°C under a constant angular velocity. Furthermore, the asphaltene particle size was simultaneously measured to investigate the relationship between deposition mass and asphaltene particle size and also to validate the concept of critical particle size. A digital microscope was used to measure the size of unstable asphaltene particles in oil. Asphaltene solubility and oil viscosity were measured to understand the deposition mechanisms. The analysis of microscopic images indicated that larger asphaltene particles are produced at higher temperatures. Although the total mass of the deposit was decreased with temperature, the deposition fraction, defined as mass fraction of total unstable asphaltene particles that deposit, was increased. Higher fraction of deposition was found for larger particles that is in contradiction to the previously introduced critical particle size concept. Additionally, the effect of solubility was found to be dominant in comparison with viscosity from the point of view of the total mass of the deposit. For the oil sample investigated in this study, a 45°C increase in temperature reduced the total mass of the deposit by 46.84%.

Variable viscosity effects on unsteady MHD reactive third-grade fluid with asymmetric convective cooling within porous Couette device

The principal motive of this study is to present a detailed account of the impact of both flow and energy profile of a time-dependent, incompressible, reactive third-grade fluid having low electrical conductivity besides variable viscosity through a porous channel accompanied by asymmetric cooling at the walls. The highly coupled equation of motion and energy manifested as non-linear partial differential equations are represented as algebraic equations using an implicit finite difference scheme and solved numerically by implementing the damped-Newton method. The solution obtained is eventually simulated using MATLAB and the resulting graphs representing the influence of non-dimensional parameters on the flow field and temperature field are discussed thoroughly. It is noted that an increase in γ values enhances non-Newtonian fluid properties which result in the thickening of the fluid and consequently fall in fluid velocity. An increase in reaction parameter and variable viscosity values remarkably enhances viscous heating source terms and contributes to the overall rise in fluid temperature. It is also observed that due to the nature of coupling of the source terms, for the majority of the non-dimensional parameters, there is a simultaneous increase or decrease in the momentum and energy profile of the fluid.

A simple model of a turbulent Couette flow, and its application to drag reduction scaling

An accurate model of a turbulent flow in a Couette device, where an effect of secondary flows induced by centripetal forces on a flow field is negligibly small, is developed and validated by experimental data found in open literature. An applicability of a laboratory Couette device for scaling turbulent drag reduction in a pipe flow is analysed. A method of drag reduction scaling, based on using only flow parameters on a solid wall, is suggested and illustrated by calculation examples. A drag reduction effect on the dimensionless torque, applied to the Couette device rotor, is illustrated by a computational example. An approach to scaling the drag reduction effect in hydraulically smooth as well as in rough wall pipes by using experimental data obtained in a Couette device is formulated.

A mathematical model for assessing shear induced bleeding risk

PurposeThe objective of this study is to develop a bleeding risk model for assessing device-induced bleeding risk in patients supported with blood contact medical devices (BCMDs). MethodsThe mathematical model for evaluating bleeding risk considers the effects of shear stress on von Willebrand factor (vWF) unfolding, high molecular weight multimers-vWF (HMWM-vWF) degradation, platelet activation and receptor shedding and platelet-vWF binding ability. Functions of the effect of shear stress on the above factors are fitted/employed and solved by the Eulerian transport equation. An axial flow-through Couette device and two clinical VADs which are HeartWare Ventricular Assist Device (HVAD) and HeartMate II (HM II) blood pump were employed to perform the simulation to evaluate platelet receptor shedding (GPIbα and GPIIb/IIIa), loss of HWMW-vWF, platelet-vWF binding ability and bleeding risk for validating the accuracy of our model. ResultsThe platelet-vWF binding ability after being subjected to high shear region in the axial flow-through Couette device predicted by our bleeding model was highly consistent with reported experimental data. As indicated by our CFD simulation results in the axial flow-through Couette device, it can find that an increase in shear stress led to a decrease in the adhesion ability of platelets on vWF, while the binding ability of vWF with platelets first increase and then decrease as shear stress elevates gradually beyond a threshold. The factor of exposure time can enhance the effect of shear stress. Additionally, the shear-induced bleeding risk predicted by our model increases with increasing shear stress and exposure time in an axial flow-through Couette device. As indicated by our numerical model, the bleeding risk in HVAD was higher than HMII, which is highly consistent with the meta-analysis based on clinical statistics. Our simulation investigations in these two clinical VADs also found that HVAD caused a higher rate of platelet receptor shedding and lower damage to HWMW-vWF than HeartMate II. The high shear stress generated in the narrow and turbulent regions of both VADs was the underlying cause of device-induced bleeding. ConclusionIn this study, the shear-induced bleeding risk predicted by our bleeding model in axial flow-through Couette device and two clinical VADs is consistent or highly correlated with experimental and clinical findings, which proves the accuracy of our bleeding model. Our bleeding model can be used to aid the development of new BCMDs with improved functional characteristics and biocompatibility, and help to reduce risk of device-induced adverse events in patients.

Food aeration: Effect of the surface-active agent type on bubble deformation and break-up in a viscous Newtonian fluid: From single bubble to process-scale

Two continuous whipping devices, a rotor–stator (RS) and a narrow angular gap unit (NAGU), were used to produce aerated food with a 25% (v/v) gas fraction target. The liquid phase was a Newtonian model-solution containing 2% (w/w) of either whey proteins (WPC), sodium caseinate (SCN), or tween 20 (TW20). Strong differences emerged regarding gas incorporation and bubble size as a function of process parameters: namely, rotation speed and residence time. To improve understanding of the results obtained at pilot-scale, a second investigation consisting in the observation of the deformation and break-up of single gas bubbles has been undertaken using successively a Couette device and an impeller close to NAGU. For proteins, the observation of single bubble deformation and break-up showed that bubble break-up occurred by tip-streaming above a well-defined critical Capillary number Cac of 0.27 and 0.5 for SCN and WPC, respectively, whereas no break-up was observed with TW20 even though Ca reached 10. The poor foaming ability obtained with TW20 could be explained by a poor break-up mechanism, promoting coalescence and gas plugs at high shear instead of gas incorporation. Conversely, protein promote tip-streaming as the major break-up mechanism at low shear rate, explaining why rotation speed is not a key process parameter. Differences observed between SCN and WPC can be attributed to diffusion limitation for SCN when a much larger surface area is generated during aeration.

Shear-banding fluid(s) under time-dependent shear flows. Part I: Spatiotemporal dynamics

We report on the response of semidilute shear-banding wormlike micelles to time-dependent flow protocols such as step stress and shear startup. We use global rheology coupled with direct optical visualizations in the Taylor–Couette flow to provide a detailed 2D description of the spatiotemporal dynamics of the shear banding flow under imposed stress. We compare these dynamics to their extensively studied counterpart under an imposed shear rate. We show that, for a given asymptotic state, the onset of banding is delayed and the transients are longer when the stress is used as a control parameter. The way the banding structure is built up strongly depends on the control parameter. In the two cases, secondary flows develop on top of the shear-banding instability: after shear startup, the interface between bands is formed in the bulk of the system and migrates inward to its stationary position in the gap of the Taylor–Couette device, before being destabilized due to elastic instability; under creep flow, the interface between bands forms at the inner wall and becomes wavy while it is still migrating outward to its steady position, leading to permanent rearrangements of the flow structure until a steady state is reached, potentially explaining longer transients. We also outline the possible mechanical signature of the onset of shear banding in terms of shape of the bulk mechanical signals, which is the subject of Part II of this work [Briole et al., J. Rheol., 65, 1201–1217 (2021)].

Dilatancy-driven secondary flows in dense granular materials

Abstract

A model of droplet breakup in a turbulent flow for a high dispersed phase holdup

A model of droplet breakup during formation of a dense emulsion in a turbulent flow is developed. Droplet fluctuation velocities, eventually causing breakup, are determined using the kinetic theory of granular media. For model validation, an experimental Couette device is employed. The dispersed and continuous phases are deionized water and mineral oil, respectively. Droplet coalescence is suppressed by a surfactant. A series of experiments is conducted for different Couette device rotation speeds and water holdups. For identification of the major droplet breakup model parameter, the critical Weber number, droplet dispersion in the Couette device is modelled by CFD-population balance A-MuSiG method implemented into the developer’s version of the Simcenter STAR-CCM+® commercial code. A good agreement between the computational and experimental data is obtained for the dispersed phase holdups in the range of 10–30%, commonly encountered in production logging of oil and water producing wells.

Branch-chain criticality and thermal explosion of Oldroyd 6-constant fluid for a generalized Couette reactive flow

This study examines Oldroyd 6-constant fluid and thermal explosion branch-chain criticality of a reactive flow in a generalized Couette device. With material consumption assumption, the reactive fluid is assumed to be actively exothermic, and the exchange of heat within the system is greater than the ambient heat exchange. Compared to the diffusion coefficient, the nondimensioned momentum and energy balance fields are influenced by a thermal Grashof number, non-Newtonian term, pressure gradient, branch-chain reaction order, and reaction initiation rate. The weighted residual collocation method is used to analytically obtain solutions to the dimensionless temperature and velocity equations as well as the bifurcation slice branch-chain solutions. The results are graphically presented, and it is revealed that a decrease in the fluid material terms will assist in managing the excessive heat generated by reaction initiation rate, and Frank Kamenetskii term. Also, a rise in the reaction branch order and reaction initiation rate can lead to system thermal runaway. Moreover, for industrial processes as obtained from the study, reactive non-Newtonian Oldroyd 6-constant fluid is thermally stable than reactive Newtonian fluid.

Investigation of Nucleation under High-Shear Conditions for a Pharmaceutical Compound in an Unseeded System

The effect of in situ high energy mixing on primary nucleation of an active pharmaceutical compound (ABT-089) has been investigated by measuring the induction time for 1, 5, and 140 mL scales via different shear-inducing mechanisms, namely, magnetic stirrer, Couette device, and high-shear rotor–stator mixer known as wet-mill in pharmaceutical industry. Experiments performed on previously untested scale and equipment show that the onset time of nucleation decreases with an increase in average energy input per unit volume of the solution (i.e., specific energy input) as previously reported (Liu, J.; Svard, M.; Rasmuson, Å.C. Influence of Agitation on Primary Nucleation in Stirred Tank Crystallizers, Cryst. Growth Des. 2015, 15, 4177–4184). The variability in the induction time is found to decrease with an increase in volume and specific energy input. Studies at different scales are compared using the Rasmuson (Liu, J.; Svard, M.; Rasmuson, ÅC. Influence of Agitation on Primary Nucleation in Stirred Tank Crystallizers, Cryst. Growth Des. 2015, 15, 4177–4184) approach based on the classical nucleation theory. It is shown that the effect of specific energy input can be adequately described by the kinetic term “A” or pre-exponential factor within the classical nucleation theory framework because the critical free-energy term appears to be constant for the same scale. A semiempirical correlation specific to ABT-089 is proposed between the energy input to a system and the average onset of primary nucleation for each of the means of shear induction. The generic approach presented in this work can be used as part of the overall development strategy to scale-up and scale-down crystallization experiments by estimating the specific energy input or the corresponding tip speed requirement to induce primary nucleation within a specified time range. However, given the practical limitations on the amount of data that can be generated and used to develop such correlations, appropriate caution is necessary in defining the scope of their applicability.

Modulated Rotating Waves in the Magnetised Spherical Couette System

We present a study devoted to a detailed description of modulated rotating waves (MRW) in the magnetized spherical Couette system. The set-up consists of a liquid metal confined between two differentially rotating spheres and subjected to an axially applied magnetic field. When the magnetic field strength is varied, several branches of MRW are obtained by means of three dimensional direct numerical simulations (DNS). The MRW originate from parent branches of rotating waves (RW) and are classified according to Rand's (Arch. Ration. Mech. Anal 79:1-37, 182) and Coughling & Marcus (J. Fluid Mech. 234:1-18,1992) theoretical description. We have found relatively large intervals of multistability of MRW at low magnetic field, corresponding to the radial jet instability known from previous studies. However, at larger magnetic field, corresponding to the return flow regime, the stability intervals of MRW are very narrow and thus they are unlikely to be found without detailed knowledge of their bifurcation point. A careful analysis of the spatio-temporal symmetries of the most energetic modes involved in the different classes of MRW will allow in the future a comparison with the HEDGEHOG experiment, a magnetized spherical Couette device hosted at the Helmholtz-Zentrum Dresden-Rossendorf.

Couette shearing device for the investigation of shear-induced damage of the primary hemostasis by left ventricular assist devices.

Continuous-flow left ventricular assist devices have evolved from short-time therapy into permanent or so-called destination therapy. One complication in long-term usage is bleeding, which is presumably attributed to shear-induced interference of left ventricular assist devices with the coagulation system. The influence of dynamic shear stresses on primary hemostasis by single or multiple passes through left ventricular assist devices was investigated. A novel Couette-type shearing device, especially fitted to simulate left ventricular assist devices with highly dynamic and repetitive stresses, was developed. To evaluate the clotting ability of the blood and thus the bleeding tendency, the closure time of the platelet function analyzer (PFA-100®, Dade Behring, Marburg, Germany) was used. The relationship of the PFA-100 closure time was fitted to measurement points with shear stress and exposure time as parameters. 76 samples of human blood collected from four different healthy donors in sodium-citrate anticoagulant solution were tested, including 20 control samples. A damage model according to the power law approach could be developed. A linear correlation of shear stress and exposure time to the PFA-100 closure time could be determined. In addition, a model was developed to calculate the increase in the PFA closure time on the basis of shear stress over time curves. With the shearing device, half-sine-wave-shaped shear stress patterns relevant to rotary blood pumps can be achieved with very good repeatability. The proposed damage model could be used to compare and optimize left ventricular assist devices under development. The tests showed a significant decrease in coagulability after only a few repetitions.

Modelling dispersion of immiscible fluids in a turbulent Couette flow

AbstractDispersion of immiscible fluids in a Couette device, in which the inner cylinder rotates whereas the outer one is immobile, is modelled. The developer's version of the STARCCM+ commercial CFD code is employed for simulations. The CFD‐population balance technique, recently implemented into the code, is a basis for the computations. The Reynolds stress turbulence model along with the Daly and Harlow transport model are employed for modelling two‐dimensional axisymmetric flow field. Formation of a stable emulsion (no coalescence) is considered. Computational results are compared with experimental data available in the literature. A low‐rate coalescence is formally introduced for accurately fitting these data. Effects of both the Couette device height and the inner to outer radius ratio on droplet size distributions are also studied using the STAR‐CCM+ CFD code. Different physical phenomena influencing the dispersion process are discussed.

Comb-like Polyoctadecyl Acrylate (POA) Wax Inhibitor Triggers the Formation of Heterogeneous Waxy Oil Gel Deposits in a Cylindrical Couette Device

In real crude-oil pipelines, the formed wax deposits could be heterogeneous along the radial or axial directions. However, studies on this aspect are scarce. In this paper, the effect of the polyoctadecyl acrylate (POA) wax inhibitor on the wax deposition of 10 wt % model waxy oil was investigated with the aid of an in-house wax deposition device, differential scanning calorimetry test, high-temperature gas chromatography–Fourier transform infrared analysis, and microscopic observation. The results showed that adding POA in the model waxy oil greatly modifies the morphology of precipitated wax crystals, thus greatly changing the wax deposition behavior of the oil. For oil sample 1 (without POA), the precipitated wax crystals (needle-like) more easily form porous network structures, causing the formation of a thick and porous wax deposit with relatively low WAT, wax conten,t and critical carbon number (CCN). With the increase of POA concentration (oil samples 2–5), the precipitated wax crystals become more...

Study of Continuous Rheological Measurements in Drilling Fluids

Abstract Drilling an oil well involves using drilling fluids that perform cleaning and cooling functions, but that most importantly maintain the fluids of the geological formation contained by hydraulic pressure. A fundamental role in predicting the hydraulic pressure of the well consists of monitoring the fluid’s rheological behavior. This paper summarizes an ongoing effort to measure, by evaluating the performance of two online viscometers, drilling fluids’ rheological behavior in real time. One online method proposes a modified Couette system. The other consists of a standard pipe viscometer with default modeling. The performances of the online devices were compared with an offline method - a Couette device commonly used in oilfields as a benchmark. For Newtonian fluids, agreement between the rheological behaviors was found for all instruments, validating the methodology proposed. For non-Newtonian fluids, there were divergences, which were investigated and their probable causes determined to be the following: homogeneity, slippage effects, and interaction in the fluid/gap interfaces. A case study demonstrated that these divergences were not significant during the prediction of hydraulic pressure, meaning that the methodology proposed has the potential to improve overall drilling performance.

An Eulerian-Eulerian formulation of suspension rheology using the finite volume method

We have adapted a well-known constitutive model formulated by Morris and Boulay (1999) that describes the stress tensor for a mixture of particles in a Newtonian liquid into a two-phase finite-volume solver. The two-phase model treats each phase with a separate continuity and momentum equation that splits the stress of the constitutive model between the two phases, with the particle pressure applied only to the particle phase in addition to source terms related to the drag of particles in the fluid. We compare the resulting model using a variety of NMR experiments, considering the flow of neutrally buoyant monodisperse particles at low Reynolds number in the following geometries: 2D simple shear flow in a Couette device, axisymmetric and 3D pressure driven flow down a pipe and in a 2D and 3D asymmetric channel bifurcation. We find excellent agreement with velocity and volume fraction profiles in all of the comparisons with experimental data without much further numerical fitting beyond the original suspension stress model.