Innovations in high throughput manufacturing of uniform emulsions and capsules

Membrane emulsification has been widely used in the manufacture of uniform soft and hard spherical particles. It is used to create uniform emulsion droplets whose sizes can be closely controlled. A disperse liquid phase is pressurised to permeate into the pores of a membrane, forming droplets in a drop-by-drop manner in a continuous phase on the other side of the membrane. The droplets formed are detached by applying well controlled detachment forces, which are result from the cross-flow of the continuous phase over the membrane surface, or the rotation of the membrane in the continuous phase. These two technologies are called cross-flow and rotating membrane emulsification, respectively. This paper presents examples of uniform complex spheres, sized from sub-micrometers to a few hundred micrometers, prepared using a pilot scale cross-flow membrane emulsification rig and a bentchtop rotating reactor. Emulsion stabilisation strategies vary from using small molecular surfactants, nanoparticles to surfactant free interfacial polymerisation. The examples demonstrate the advantages and versatility in formulation and manufacture of precisely size- and structure-controlled products using membranes.     

Taylor vortices between almost cylindrical boundaries

Summary We consider a modified Taylor problem, with the fluid flowing between a rotating inner circular cylinder and an outer stationary surface whose radius is a constant plus a small and slowly varying function of the axial co-ordinate z. This variation is chosen in such a way that the flow is locally more unstable near z=0 than near z=±, so that Taylor vortices appear more readily near z=0. The theory is developed to show how vortices of strength varying with z develop as the speed of rotation is increased through a critical value which is a perturbation of the classical value. Wave number changes in the axial direction are also calculated.     

Development of an Imaging System and Its Application in the Study of Cutting Fluid Atomization in a Turning Process

Airborne inhalable particulates in the workplace can represent a significant health hazard, and one of the primary sources of particles is mist produced through the application of cutting fluids in machining operations. One of the principal mechanisms associated with cutting fluid mist formation is atomization. Atomization is studied by applying cutting fluid to a rotating workpiece such as found in a turning process. In order to properly study the atomization mechanism, an imaging system was developed. This system extends the size measurement range typically achievable with aerosol sampling devices to include larger particles. Experimental observations reveal that workpiece rotation speed and cutting fluid flow rate have significant effects on the size of the droplets produced by the atomization mechanism. With respect to atomization, the technical literature describes models for fluid interaction with the rotating workpiece and droplet formation via drop, ligament, and film formation modes. Experimental measurements are compared with model predictions. For a range of rotation speeds and fluid application flow rates, the experimental data are seen to compare favorably with the model predictions.     

Travelling Taylor vortices in closed systems

Summary Travelling Taylor vortices between conical cylinders and a cone-cylinder combination are described. The flow results from a rotating inner cone and an outer shell at rest. Due to different centrifugal forces on the cone's surface one obtains a three-dimensional laminar basic flow and regions of subcritical and supercritical flows in the annulus. By some specific bifurcation sequences a rich variety of flow patterns occurs. The generated Taylor vortices can be steady or unsteady, toroidal or helical. Depending on different initial and boundary conditions, toroidal or helical vortices travel through a closed system. Furthermore, combinations of steady toroidal and unsteady helical vortices are possible. The influence of the governing parameters is discussed.     

Particle defects and related properties of metallic powders produced by plasma rotating electrode process

Flowability, particle size distribution and particle inner pore features for powders of Ti-6Al-4V, 316-steel, and Co-29Cr-6Mo alloys produced by plasma rotating electrode process (PREP) at various rotation speeds are analyzed by using scanning electron microscopy (SEM) and synchrotron X-ray computed tomography (CT). The results show that powder flowability is related to particle size distribution, surface morphology and dynamic friction coefficient of the alloy itself. This results in the higher powder flowability at low rotation speed than that at high rotation speed. Average particle size is roughly proportional to the square root of the reciprocal of rotation speed. In addition, particle size has an important effect on the particle porosity and the number faction of hollow powder in coarse powder is obviously larger than that in fine powder. Meanwhile, the alloy composition also plays a key role on porosity due to the various surface tension of alloys.     

3-mode Interactions with O(2) Symmetry and a Model for Taylor-Couette flow

We analyse the bifurcations of a general ordinary dififerential equation where is equivariant under an action of the group O(2) on. The equation represents the most general nonlinear local interaction of three O(2)-symmetric modes:a steady-state mode with mode-number k, and two periodic (Hopf) modes with mode-numbers l and m. The parameter λ is a bifurcation parameter, and α₁, α₂are unfolding parameters that split the individual modes apart. The system is assumed to be in Birkhoff normal form, so that f also commutes with an action of the 2-torus T². We discuss the existence and stability of bifurcating branches and how these break the O(2) × T² symmetry.Depending on the precise mode-numbers k l m we find up to 31 symmetry classes of possible solutions including six that combine all three modes, and thus cannot be found in any 2-mode interaction. We also discuss the possible occurrence of Sacher-Naimark torus bifurcations, providing a further 10 solution types, and 'slow drift'bifurcations.

This 10-dimensional system can occur generically in O(2)-symmetric bifurcation problems having two extra parameters, and in principle is applicable to a wide range of physical systems. The discussion here is motivated by the observed pattern formation in the Taylor–Couette system, the flow of a fluid contained between coaxial rotating cylinders. It arises by seeking a 'hidden organizing centre' that combines two previous mode-interaction models of this system: a 6-dimensional Hopf–steady-state model due to Chossat and looss (1985) and Golubitsky and Stewart (1986), and an 8-dimensional Hopf–Hopf model due to Chossat, Demay and looss (1987). We interpret the general results on the 10-dimensional system in the context of Taylor–Couette flow, giving schematic pictures of the associated flow patterns. The model incorporates almost all of the observed non-chaotic flows in the Taylor–Couette experiment into a single finite-dimensional dynamical system. It predicts the possible occur- rence of four new flow patterns (corresponding to four of the six possible solutions that combine all three modes). Theseform invariant 3-tori, and may be described as superimposed twisted vortices, superimposed wavy vortices, and two types of twisted wavy vortices. Possible torus bifurcations from states in the 10-dimensional model include various modulated spirals, three types of modulated twisted vortices, three types of modulated wavy vortices, modulated superimposed spirals, modulated interpenetrating spirals, modulated superimposed ribbons, and modulated interpenetrating ribbons. However, whether any of these new states and torus bifurcations can actually occur in Taylor–Couette flow at suitable parameter values, and if so whether they can occur stably, depend upon more detailed numerical calculations than we have performed     

Symmetric and asymmetric Taylor vortex flow in spherical gaps

Summary The rotationally symmetric flow between two concentric rotating spheres is investigated both theoretically and experimentally. The non-uniqueness of the supercritical flow exhibits three different modes with zero, one and two Taylor vortices in each hemisphere. These modes are realized by different accelerations of the inner sphere from the state at rest. A initial value code, based on a finite difference method, is used for the numerical simulation. The existence regions of the different supercritical flows are connected with symmetric and asymmetric transitions. It is found, that a steady state can exist asymmetric with respect to the equator. The flow is analyzed by plotting the size of the Taylor vortices, the depending variables , ,V, the velocity distributions and the torque. A comparison between theory and experiments for the observed modes of flow is given.     

乳状液制备新工艺——膜乳化过程实验研究

用膜乳化系统制备了Ｏ／Ｗ型乳状液,考察了乳化时间、平均膜孔径、壁面剪应力、膜两侧压差和乳化剂等因素对乳化效果的影响．实验显示,分散相液滴平均直径不随乳化时间而变化;在此条件下,该直径约是膜平均孔径的５～１２倍．随着连续相一侧壁面剪应力的增大液滴平均直径减小,但当壁面剪应力大到一定值后,减小的幅度变得很小．增大膜平均孔径和膜两侧压差都将增加分散相透过膜的通量．此外,乳化剂分子的吸附速度越快,分散相液滴平均直径越小．     

Particle Separation in an Annular Converging Channel with an Inner Rotating Permeable Baffle

The relation between the separation efficiency of solid particles and the stability of the helical flow of a viscous fluid in a converging channel with an inner rotating permeable cylindrical baffle has been studied. The profiles of the axial and tangential velocities and the separation efficiency of solid particles have been calculated based on the numerical solution of a system of equations describing the hydrodynamics of two-phase media. Analysis of the obtained solutions shows that vortices having an effect on particle separation can appear in the converging channel. Moreover, the larger the size of the converging annular channel, the earlier a loss of stability occurs. It has been found that the formation of vortices is impossible for some flow regimes and, as a result of fluid flow stabilization, the fraction of particles settled on the permeable cylindrical baffle decreases. It has been shown that those regime parameters at which a helical flow exists should be selected for the development of combined action units involving filtering and the separation of the solid dispersed phase.     

Phase slip solutions in magnetically modulated Taylor–Couette flow

We numerically investigate Taylor–Couette flow in a wide-gap configuration, with \({r_i/r_o=1/2}\), the inner cylinder rotating, and the outer cylinder stationary. The fluid is taken to be electrically conducting, and a magnetic field of the form \({B_z\approx(1 + \cos(2\pi z/z_0))/2}\) is externally imposed, where the wavelength \({z_0=50(r_o-r_i)}\). Taylor vortices form where the field is weak, but not where it is strong. As the Reynolds number measuring the rotation rate is increased, the initial onset of vortices involves phase slip events, whereby pairs of Taylor vortices are periodically formed and then drift outward, away from the midplane where \({B_z=0}\). Subsequent bifurcations lead to a variety of other solutions, including ones both symmetric and asymmetric about the midplane. For even larger Reynolds numbers, a different type of phase slip arises, in which vortices form at the outer edges of the pattern and drift inward, disappearing abruptly at a certain point. These solutions can also be symmetric or asymmetric about the midplane and co-exist at the same Reynolds number. Many of the dynamics of these phase slip solutions are qualitatively similar to previous results in geometrically ramped Taylor–Couette flows.     

Numerical methods for two-fluid hydrodynamics: Application to the Taylor vortex flow of superfluid helium II

We describe the numerical method which we have developed to solve for the first time the fully nonlinear HVBK equations. These equations generalise Landau's two fluid model to take into account the presence of quantised vortices. We apply the method to investigate the flow pattern of helium II between rotating concentric cylinders (Taylor vortex flow) at increasing Reynolds numbers. We compare the results against classical Taylor vortex flow.     

Transition from Taylor vortices to cross-flow instabilities

Summary We present experimental results of fluid flow instabilities between different rotating surfaces. We start withcounter-rotating Taylor vortices between two coaxial cylinders. We go over to rotating cones with increasing apex angle. Due to the growing cross-flow we finally end up with spiral vortices allrotating in the same direction between a rotating disk and a housing. Figure 13 gives a complete survey of these results. We discuss the transition from one vortex system to the other in detail.Dedicated to Prof. Dr. Dr. h. c. mult. S. Wittig on the occasion of his 60th birthday     

Flow visualization studies of vortices

An actual vortex in the Kármán vortex street downstream of a circular cylinder has a core of finite dimension which increases downstream. The circulation of the vortex is nearly constant. The ratiob/a which is 0.281 according to the theory of Kármán, grows from 0.2 to 0.4 in the near wake. In the flow about a circular cylinder rotating in a uniform flow, a Kármán vortex street, Görtler-type vortices and Taylor vortices are generated at the same time. In the flow about a circular cylinder impulsively started with a constant velocity, the primary twin vortices behind the cylinder induce secondary twin vortices near the separation point. At the beginning of the motion, the separation does not occur even though a reverse flow is observed in the boundary layer. Mutual slip-through of a pair of vortex rings was achieved by increasing the Reynolds number. A vortex ring rebounds from a plane surface due to the separation of the flow on the surface induced by the vortex ring, and the secondary vortex ring is formed from the separated shear layer.     

Stability of power law fluid flow between rotating cylinders

The centrifugal instability of power law fluid flow when the fluid fills the gap between two rotating concentric cylinders of infinite length is addressed. The instability of the circular Couette flow is determined via linear stability analysis. In the narrow gap case, the critical Taylor number is determined analytically, while in the general gap case, a finite-difference numerical method is employed. The results are shown to be in agreement with existing theoretical and experimental findings. The super-critical flow is investigated by means of a weakly non-linear analysis method. The Taylor-vortex flow (the secondary stable flow) is obtained. The instability of this flow is determined as we present the critical Taylor number when the Taylor vortices begin to exhibit a waviness in the azimuth     

Segregation behavior of particles with Gaussian distributions in the rotating drum with rolling regime

The mixing and segregation of granular materials are essential to provide valuable insights and references for practical industrial production. In this paper, the segregation behaviors of particles with Gaussian distributions and 40% filling level in the rotating drum with rolling regime were numerically studied by the discrete element method. The effects of rotation speed and particle size parameter λ (size ratio of the largest versus smallest particles) on the segregation behavior (mixing index, segregation rate), flow characteristics (particle velocity and trajectory, gyration degree and radius, particle size distributions) and the microscopic properties (collision, contact force, axial diffusion, and kinetic energy) of granular systems were systematically investigated. The results show that the segregation rate and degree of particles with Gaussian distributions gradually increase with the increase of the rotation speed and particle size parameter λ. The radial and axial segregation patterns become more obvious with the increase of λ. And the variation of the flow characteristics of particles with different sizes in the same system is also inconsistent. The microscopic properties of Gaussian-dispersed particles change with the rotation speed and λ. The rapid radial segregation depends on the larger pores existed in the granular system, which leads to a gradual increase of the axial dispersion coefficient of large particles and a gradual decrease of the axial dispersion coefficient of small particles.     

Characteristics and atomization behavior of Ti-6Al-4V powder produced by plasma rotating electrode process

In the present research, the characteristics and atomization behavior of Ti-6Al-4V powders produced by plasma rotating electrode process (PREP) with different rotation speeds were investigated. Three kinds of particles in the as-PREPed powders are observed: spherical particles, satellite particles and irregular particles. The mean particle size of the PREP powder decreases and its distribution becomes narrower gradually with increasing rotation speed. PREP powder at higher rotation speed demonstrates lower fractions of both satellite particles and irregular particles. By observing the residual electrode tip, it is considered that the irregular particles with corner or flat shape are possibly caused by the tearing of liquid film under the action of centrifugal force and shear force during the atomization process.     

Shear controllable synthesis of barium sulfate particles using lobed inner cylinder Taylor-Couette flow reactor

A novel lobed inner cylinder assembled in Taylor-Couette flow reactor (LTC) has been adopted to synthesize barium sulfate particles. The fluid dynamics that affects synthesis of particles using both the LTC and the classical Taylor-Couette flow reactor (CTC) was investigated through CFD modelling and experiments. The results have demonstrated that the Taylor vortices and turbulence induced shear rate distribution in the reactors have a significant influence on the final particle size distribution. The narrower shear rate distribution in the LTC is beneficial to the synthesis of particles with smaller size. The local turbulence intensification in the intra-Taylor vortices in the LTC effectively reduces the low shear strain regions. A strong correlation between the synthesized particle size and the local turbulent dissipation rate is existing. Shear induced by small turbulent eddies can inhibit particle growth. The LTC can be used for effectively shear controllable synthesis of particles.     

旋转填充床中反溶剂重结晶法制备超细硫酸沙丁胺醇实验研究

本文在旋转填充床中用反溶剂重结晶方法对硫酸沙丁胺醇原料药品进行了细化.研究了结晶温度、反溶剂与硫酸沙丁胺醇水溶液流量比、旋转填充床转速等操作参数对硫酸沙丁胺醇颗粒大小及收率的影响.实验结果表明,采用较低的结晶温度、较大流量比和较大旋转填充床转速可以得到粒度小于500nm的硫酸沙丁胺醇颗粒.     

Rotating Inclined Cylinder and the Effect of the Tilt Angle on Vortices

We study numerically some possible vortex configurations in a rotating cylinder that is tilted with respect to the rotation axis and where different numbers of vortices can be present at given rotation velocity. In a long cylinder at small tilt angles the vortices tend to align along the cylinder axis and not along the rotation axis. We also show that the axial flow along the cylinder axis, caused by the tilt, will result in the Ostermeier-Glaberson instability above some critical tilt angle. When the vortices become unstable the final state often appears to be a dynamical steady state, which may contain turbulent regions where new vortices are constantly created. These new vortices push other vortices in regions with laminar flow towards the top and bottom ends of the cylinder where they finally annihilate. Experimentally the inclined cylinder could be a convenient environment to create long lasting turbulence with a polarization which can be adjusted with the tilt angle.     

Stability of a thin viscous fluid film flowing down a rotating non-uniformly heated inclined plane

A thin viscous liquid film flowing down a rotating non-uniformly heated inclined plane is investigated. It is assumed that the rotation is small and the region of investigation is very far from the axis of rotation, so that the centrifugal force has a dominant role in the instability of the investigated region. Therefore, we have derived a Benney-like free surface evolution equation on the basis of a long-wave (small wave number) approximation and not included the Coriolis effects in the expansion of the dependent variables. Further, a linear and a weakly nonlinear study have been carried out. The linear study reveals that the growth of linear perturbation is independent of the Rossby number Ro, that is invariant with the Coriolis effect, while the linear phase speed c _r depends on Ro as well as on the Taylor number Ta. It also reveals that as Ta increases the stable zone decreases, and the influence of Ta is stronger for greater inclination of the rotating inclined plane. Again, it is found that the Marangoni number Mn has similar qualitative (destabilizing) behavior as Ta, but the destabilizing behavior of Ta is more at high Mn than at low Mn. The relation between the parameters Ta and Ro gives a unified parameter Ta_rot, which reflects the effect of rotation, and we found that the linear phase speed c _r first decreases with Ta_rot up to a critical value and then increases with Ta_rot. This is due to the fact that the Coriolis force is dominant at very small rotation, while for relatively large rotation the centrifugal force dominates the flow field. The weakly nonlinear study reveals that the effect of rotation appears in the form of both Coriolis and centrifugal force into the growth of finite amplitude perturbations in contrast to the growth of the infinitesimal perturbations where the rotation arrives in the form of centrifugal force only. Also, it plays significant role in the different stability zones, amplitudes of sub/super critical disturbances and nonlinear phase speed.