Couette-type Flow Research Articles

Dough processing in a Couette-type device with varying eccentricity: Effect on glutenin macro-polymer properties and dough micro-structure

Dough mixing involves a combination of different deformation flows, e.g. shear and elongation. The complicated nature of mixing process makes it difficult to understand dough processing at a mechanistic level. A new Couette device allowed the effects of shear flow on the physical properties of glutenin macro-polymer (GMP) and micro-structure formation of the dough to be studied. Steady shear deformation using concentric Couette-type flow did not decrease GMP content or size of glutenin particles. Confocal scanning laser microscopy revealed the formation of interconnected gluten domains indicating the development of a gluten network. In an eccentric Couette configuration the results depended on the degree of eccentricity. A higher degree of eccentricity and a longer processing time led to considerable reduction in GMP content and size of glutenin particles. The micro-structural change in the narrow gap regions of the eccentric cell occurred early in processing, leading to a break up of large protein domains, and a microscopically more homogeneous dough. Transient high shear flow led to elongation and break up of the macroscopic gluten network. In low shear regions of the eccentric cell (wider gap settings), reformation or aggregation of protein domains was observed. Thus, the gluten aggregation–break up mechanisms are strongly influenced by the local flow profile in a conventional mixer. The impact of different types of shear flow must be taken into account in the design of dough mixers.

Influence of shear flow on the preparation of polymer layered silicate nanocomposites

In this paper the influence of melt-processing on the final polymer/layered silicate nanocomposite morphology is discussed. In particular the role of shear forces on the transformation of the original large clay agglomerates is of interest. Several polymer nanocomposites were prepared by melt-extrusion, involving polycaprolactone, poly(ethylene oxide), polyamide-12 or polyamide-6 as the matrix polymer. The nanocomposite morphology was characterised by X-ray diffraction and transmission electron microscopy and the clay tactoid morphology with polarised optical microscopy and scanning electron microscopy. The development of the tactoid and nanocomposite morphology during melt-mixing under shear was studied time-resolved by optical microscopy in conjunction with a rheometer and synchrotron X-ray scattering together with a Couette type flow cell. The shear forces in the melt-preparation of polymer layered mineral nanocomposites facilitate the break-up of large-sized agglomerates, whereas the extent of further exfoliation of the mineral layers is determined by the compatibility between the polymer matrix and the mineral layers rather than by shear forces.

Using process intensification in the actinide processing industry

AbstractAll industrially significant actinides have hazards associated with their storage and handling. All are radioactive and potentially fissile which limits the amount of material that can be processed in a given unit operation to prevent a criticality accident. To protect workers from the radiation and direct exposure to these toxic elements, processing is done in remote‐handling facilities or within engineered barriers like glove boxes. Such facilities are expensive to build, operate, and maintain. Actinides also have high waste handling, storage and disposal costs due to their radioactivity and toxicity. These processing constraints make actinide processing an excellent candidate for process intensification as they are separated from undesirable fission products or purified to usable product. Using specially designed equipment that enhances the mixing and mass transfer or combining several unit operations in single unit are typical of process intensification. Annular centrifugal contactors are an excellent example of applying Taylor–Couette type flow to mix two immiscible fluids and then separating them centrifugally. Hence, two operations are combined in one unit.© 2003 Society of Chemical Industry

Scaling Law for Couette-Poiseuille Type Turbulent Flow and Study on 1/2 Power Law and Core Regions.

Direct numerical simulations of fully developed Couette-Poiseuille type turbulent flow are performed. The velocity law of this flow depends on the Reynolds number and two non-dimensional parameters of the shear stress gradient. We pay a particular attention to the effect of the shear stress gradient on the velocity distribution on the Couette-type flow. Computational results are dependent on the three non-dimensional parameters and are compared with theoretical laws and existing experimental data. The law of the mean velocity profile for Couette-Poiseuille type turbulent flow is considered in the regions characterized by 1/2-power law and velocity defect law. In particular, it is shown that the influence of turbulent diffusion from the opposite wall appears in the flow with large shear stress gradient and 1/2-power law is restricted to narrow region.

Turbulence Statistics of CouettePoiseuille Turbulent Flow. 1st Report. Turbulence Intensities.

Turbulence intensities in Couette·Poiseuille flow, developed between stationary and moving walls, have been measured by I-and X-type hot wires. The intensities in the wall region are affected by non-dimensional shear stress gradient parameter μ (≡u3*/av), but not by Reynolds number Re* (≡hu*/v). As|μ|decreases, distributions of streamwise and wall-normal turbulence intensities shift upward or downward from those of plane-Couette flow depending on the sign of μ. In the turbulent core region, turbulence intensities of Poiseuille-type flow distribute quite differently from that of Couette-type flow. The effective parameter in this region is β, but the effect of β on the turbulence intensities is obscured by the low Reynolds number effect.

Calculation of plane turbulent Couette-Poiseuille flows with a modified k-ε model

Suitable modifications to the k—ε model are proposed for the calculation of turbulent Couette-Poiseuille flows. In the case of pure Couette flow a logarithmic expression for the turbulent kinetic energy could be derived which is valid over the entire fully turbulent region. The basic idea for numerical computations is the deviation from the concept of constant c μ . In the case of Couette-type flows proper distributions of this model parameter could be found. In Poiseuille-type flows the application of an extended eddy-diffusivity approach for the turbulent shear stress leads to results which satisfactorily correspond to the measurements.

Shear Alignment of a Rhombohedral Mesh Phase in Aqueous Mixtures of a Long Chain Nonionic Surfactant

In a recent paper (Burgoyne, J.; Holmes, M. C.; Tiddy, G. J. T. J. Phys. Chem. 1995, 99, 6054) we showed that binary mixtures of the poly(oxyethylene) surfactant, nonaethylene glycol mono(11-oxa-14,18,22,26-tetramethylheptacosyl) ether (C30EO9), in 2H2O exhibited an extensive intermediate mesh phase between a higher temperature lamellar phase and a lower temperature hexagonal phase. Here, we present small angle neutron scattering results obtained from a sample of the hexagonal phase shear aligned in a couette type flow cell and then gently heated into the intermediate mesh phase. The scattering pattern shows a 6-fold symmetry of the (110) reflection and indicates that the structure of the phase is a six connected rhombohedral mesh with space group R3m. The unusual structure is explained by the competition between the need to reduce surface curvature on raising temperature because of decreasing head group hydration and the repulsive interaggregate head group overlap (HGO) interaction.

Mean Velocity Profiles of CouettePoiseuille-Type Turburent Flow.

Mean velocity profiles of Couette·Poiseuille-type turbulent flow developed between fixed and moving walls have been measured. The relevant parameters for the wall, 1/2-power and core region are μ(=μ3*/αν, where α=1/ρ·dτ/dy) and Re*'(=u*h'/ν), β'(=αh'/u2*) and Re*', and β(=αh/u2*) and Re* (=u*h/ν) respectively. The effects of these parameters on the velocity profiles in each region considered. Except for the core region of the Couette-type flow, each region has a reference wall. In the wall region, the wall law varies largely with μ but slightly with Re*'. Typically, the additive constant B of the logarithmic-velocity low (or Van-Driest damping factor A+) is shown to depend only on μ. The 1/2-power velocity law depends not only on β', as well known, but also Re*' under low Re conditions. In the core region, the normalized eddy viscosity εT/u*h' is constant irrespective of Re* and β for Poiseuille-type flow while it depends on both Re* and β for Couette-type flow. This indicates that the turbulent structures of the core region are quite different between Poiseuille-and Couette-type flows.

Viscous damping model for laterally oscillating microstructures

Viscous energy loss in oscillating fluid-film dampers that provide frictional shear for laterally-driven planar microstructures is investigated. It is found that Stokes-type fluid motion models viscous damping more accurately than Couette-type flow field. This paper characterizes the damping property of a fluid layer in terms of viscous energy dissipation, then derives analytic damping formulae for practical Q estimation. Theoretical Q-factors are compared to the experimental values, measured from surface-micromachined polysilicon resonators. Data reported by previous investigators are also analyzed and compared. The experimental results indicate that the Stokes-type damping model presents a more general damping treatment with better Q estimation, although discrepancies of 10 to 20% still remain between the estimated and measured Q. >

Plasma filtration in Couette flow membrane devices.

This report investigates the effects of transmembrane pressure (ptm), rotation speed, and membrane characteristics on the performance of a rotating membrane device for separating plasma from whole blood. This device consists of 58 cm2 polymeric membrane rotating at high speed (3,000-4,000 r/min) inside a concentric cylinder and produces a Couette type flow in a gap 0.9 mm thick. Blood enters tangentially at the top, exits tangentially at bottom, and plasma is collected by an axial duct. It is found that this device yields maximum filtration velocities (plasma filtration flux per unit area) in the range of 0.5-0.8 cm/min, which are 10-20 times larger than those obtained by using hollow fiber plasma filters. This high performance is not due to the effect of centrifugal forces on red blood cells but rather to the very high shear rates, on the order of 20,000 sec-1, generated in the gap by toroidal flow instabilities (Taylor vortices). When a 0.8 micron pore size Nuclepore (polycarbonate) membrane is used, the filtration velocity presents a narrow peak of 0.6 cm/min at ptm = 10 mm Hg at 3,000 r/min and decreases to 0.35 cm/min at larger ptm. With a 0.5-micron pore nylon membrane the filtration speed increases continuously with ptm and reaches a plateau of 0.5 cm/min.

Couette flow of rigid/hardening solids

Steady Couette-type flow of rigid/linear-hardening solids is investigated. Material behaviour is governed by the von-Mises flow rule. The general flow problem is reduced to a semi-coupled system of two partial differential equations. A few possible boundary conditions are suggested. An exact solution for the plane strain problem is derived. That solution is used, in conjunction with average stress boundary data, for simulating a simple Couette-type flow problem through a curved tube with a rectangular cross section. It is shown that wall friction induces plastic boundary layers into the material. The essential features of these boundary layers are discussed.

Flow Transition Criteria in a Journal Bearing

High speed Couette type flow was studied for small clearance ratios (C/R = 0.0055 and 0.0031). Water flow pattern visualiszations and torque measurements were performed. Results show that Taylor vortices occur at values predicted by theory, they precede turbulence effects and cause an increase in torque which depends on the clearance ratio. Transition between vortex and turbulent flow is gradual and appears to depend on the Taylor number. Taylor vortices can be found in plain bearings.

A generalized couette-type flow with variable viscosity

In the present paper, a study is made of liquid flow with variable viscosity in plane and annular channels, liquid being injected or sucked through their porous surfaces. The solution is obtained of the dynamic and thermal problems for the case in which the flow is caused by a longitudinal pressure gradient and motion of one of the channel surfaces.

Steady-State Flow of a Gelling Material Between Rotating Concentric Cylinders

In a previous paper the authors proposed constitutive equations for the analytical description of gelling incompressible materials. This set of equations is used to predict the steady-state Couette-type flow between concentric cylinders under relative rotation. The solution for the thixotropic material is given in terms of five material parameters accounting for the phenomena of “breakdown” and “recovery” in rigidity. Analysis shows that dependence of the solution on the loading history occurs if a certain inequality is satisfied by the five material parameters.

On the Flow Past a Sphere at Hypersonic Speed with a Magnetic Field

Heat Transfer and Recovery Factor in a Laminar Boundary Layer With Arbitrary Pressure Gradient and Wall Temperature Distribution BERNARD L E F U R 682 An Alternative Formulation of the Problem of Flutter in Real Fluids. W E N H W A C H U AND H. NORMAN ABRAMSON 683 Shock Waves and Dissipation in a Resonance Tube ASCHER H. SHAPIRO 684 a Generalized Porous-Wall Couette-Type Flow. . . . G. M. LILLEY 685 The Modified Goodman Diagram and Random Vibration. . H. C. SCHJELDERUP 686 Calculation by the Integral Method of the Effect of Fluid Injection Upon an Isothermal Boundary Layer MILTON M. K L E I N 686 Comments on On Slip-Flow Heat Transfer to a Flat Plate DONALD E. NESTLER 687 nr^HE CONSTANT DENSITY SOLUTION to the hypersonic inviscid flow past a sphere obtained by Lighthill has been extended to the case of a sphere with a radial magnetic field in a conducting fluid by Kemp. The solution obtained by Kemp uses the assumption that the magnetic Reynolds Number is small and, hence, the magnetic field induced by the flow is not considered. Since the flow is assumed to have constant density in the region behind the bow shock wave, the problem reduces to consideration of the effect of a ponderomotive force produced by the interaction of the magnetic field with the moving conducting fluid on the flow behind the bow shock wave. The author became interested in this problem in making an attempt to extend the Newtonian theory of hypersonic flow, reviewed by Hayes and Probstein, to the magnetic field problem. Unfortunately, the result obtained did not reduce to that of Kemp in the region of the stagnation point. The author, therefore, in trying to explain this anomaly, found it necessary to examine Kemp's solution in some detail. In doing this, it was found that result as given by Kemp is incorrect due to assumptions of analyticity of the functions concerned. Kemp chooses to obtain the solution for large density ratio across the shock wave using a simple Taylor expansion to span the region between the shock and body. That this approach is beset with dangers can be seen directly from the equations concerned. The type of difficulty encountered is that discussed by Lighthill where the first