Particle-size and velocity measurements in flowing conditions using dynamic light scattering

The noninvasive optical technique of dynamic light scattering (DLS) is routinely used to characterize dilute and transparent submicrometer particle dispersions in laboratory environments. A variety of industrial and biological applications would, however, greatly benefit from on-line monitoring of dispersions under flowing conditions. We present a model experiment to study flowing dispersions of polystyrene latex particles of varying sizes under varying flow conditions by using a newly developed fiber-optic DLS probe. A modified correlation function proposed in an earlier study is applied to the analysis of extracting the size and velocity of laminar flowing particulate dispersions. The complementary technique of laser Doppler velocimetry is also used to measure the speed of moving particles to confirm the DLS findings.     

Fiber-Optic Sensor for Web Velocity Measurement

The design and development of a new fiber-optic sensor for measuring the velocity of a continuous material (also called a web) in material processing systems is described. The development of the proposed sensor is based on the dual beam laser Doppler velocimetry technique and the unique properties of different types of optical fibers. The developed sensor is capable of measuring the true web transport velocity as opposed to the existing methods which infer web transport velocity based on the roller angular speed. Since the sensor design utilizes fibers, signal processing can be performed away from the measurement area, and as a result the sensor can be used in harsh environments within the web processing line. The proposed sensor has been constructed and experiments have been conducted on an experimental web platform. The performance of the sensor is evaluated for a range of web velocities and different web materials. Sensor design, its construction, and a representative sample of the results are presented and discussed.     

New technique for measuring low fiber-optic attenuation usingdouble square-law detection

A new technique for precision measurement of low fiber-optic attenuation has been developed using double square-law characteristics in a subcarrier lightwave detection system. It magnifies the effect of a small attenuation four times and a 0.01 dB change in optical attenuation produces a 0.04 dB change in electrical attenuation. The present system is capable of measuring attenuation changes less than 0.01 dB with system resolution 0.001 dB     

Stagnant vortex flow

With the aid of the vorticity transport equation it is shown that in inviscid, incompressible, axially symmetric vortex flow the axial vorticity component near the axis of the vortex approaches zero if the axial velocity component approaches a stagnation point, and vice versa, the axial vorticity component is increased, if the axial flow is accelerated. This result, obtained in earlier investigations by simplifying the momentum equations for the neighborhood of the axis of the vortex, is already contained in the vorticity transport equation as formulated by von Helmholtz in 1858. In laminar flow, with viscous forces acting near the stagnation point, the angular velocity does not necessarily vanish with the axial velocity component. These questions are discussed in the following.     

Numerical investigations of laminar flow characteristics in helically finned pipes

The laminar flow in a helically finned pipe has been considered. The steady solutions have been obtained by numerical integration of the Navier-Stokes equations formulated in a cylindrical coordinate system. Three-dimensional fins have been embedded in the structured mesh as immersed boundaries. A helical fin generates a swirling flow which exhibits a helical symmetry. In the presence of a single fin, the circumferential velocity turned out to increase both with fin height and fin angle. The core region with high axial velocity is shifted away from the pipe axis. High levels of axial vorticity caused by the fin-induced swirl are observed in the vicinity of the tip of the fin whereas substantial vorticity of opposite sign is produced in the wall-layer near the suction side of the fin. In the presence of two fins with the same pitch, i.e., a double helix, the symmetry about a diametrical plane gave rise to a keyhole-shaped axial velocity distribution. The drag coefficient was increased by all the fin configurations considered when compared to regular pipe flow at the same Reynolds number.     

An effect of sudden circumferential strain on the laminar boundary layer on a rotating cylinder in an axial flow

Summary The laminar boundary layer which develops on a rotating thin cylinder fitted with an aft-section rotating with an angular velocity different from that of a fore-section is examined numerically. This problem concerns a relaxation process of the boundary layer subjected to a sudden circumferential rate of strain. Two methods are adopted: one is to regard the flow on the aft-cylinder as perturbations of that on the fore-section, and the other is to approximate the discontinuous change in the angular velocity by the cumulative normal distribution function. It is shown that the flow fields are largely influenced by the degree of favorable pressure gradient produced in the boundary layer. Especially, in case of flow passing onto the aft-section with a smaller angular velocity, adverse pressure gradient is induced immediately after the junction between two cylinders, and when the degree of the discontinuity is increased, flow separation can be provoken.With 11 Figures     

Unsteady mixed convection flow of a thermomicropolar fluid on a long thin vertical cylinder

The unsteady laminar mixed convection boundary layer flow of a thermomicropolar fluid over a long thin vertical cylinder has been studied when the free stream velocity varies with time. The coupled nonlinear partial differential equations with three independent variables governing the flow have been solved numerically using an implicit finite difference scheme in combination with the quasilinearization technique. The results show that the buoyancy, curvature and suction parameters, in general, enhance the skin friction, heat transfer and gradient of microrotation, but the effect of injection is just opposite. The skin friction and heat transfer for the micropolar fluid are considerably less than those for the Newtonian fluids. The effect of microrotation parameter is appreciable only on the microrotation gradient. The effect of the Prandtl number is appreciable on the skin friction, heat transfer and gradient of microtation.     

Analytical solution of combined electroosmotic/pressure driven flows in two-dimensional straight channels: finite Debye layer effects

Analytical results for the velocity distribution, mass flow rate, pressure gradient, wall shear stress, and vorticity in mixed electroosmotic/pressure driven flows are presented for two-dimensional straight channel geometry. We particularly analyze the electric double-layer (EDL) region near the walls and define three new concepts based on the electroosmotic potential distribution. These are the effective EDL thickness, the EDL displacement thickness, and the EDL vorticity thickness. We show that imposing Helmholtz-Smoluchowski velocity at the edge of the EDL as the velocity matching condition between the EDL and the bulk flow region is incomplete under spatial bulk flow variations across the finite EDL. However, the Helmholtz-Smoluchowski velocity can be used as the appropriate slip velocity on the wall. We discuss the limitations of this approach in satisfying the global conservation laws.     

Multipole expansions in Stokes flow

Maxwell's theory of multipoles is extended from potential theory to Stokes flow field, and from spherical to spheroidal geometry. The expansion is based on an exterior integral representation of the velocity and the pressure field of Stokes flow as well as the appropriate fundamental solution. It is shown that the velocity field is expandable in terms of five different multipoles, four of which are weighted multipoles. On the other hand, the pressure as well as the vorticity field, have multipole expansions that involve only the non-weighted multipoles. In fact, a more general result is demonstrated according to which the pressure and the vorticity are given as the scalar and the vector invariants of the same harmonic dyadic field. The importance of the multipole expansion for the velocity and the pressure field is well known, and it refers both to the theoretical understanding of the flow, as well as to practical applications and numerical implementations.     

Differential low-coherence interferometry for <Emphasis Type="Italic">in situ</Emphasis> diagnostics of transparent structures

We describe and demonstrate a new differential method capable of measuring the profiles of transparent structures. Based on fiber-optic low-coherence interferometry and possessing a high noise immunity, the proposed technique can be used for the noncontact in situ diagnostics of microstructures under extremal conditions.     

Monochromatic heterodyne fiber-optic profile sensor for spatially resolved velocity measurements with frequency division multiplexing

Investigating shear flows is important in technical applications as well as in fundamental research. Velocity measurements with high spatial resolution are necessary. Laser Doppler anemometry allows nonintrusive precise measurements, but the spatial resolution is limited by the size of the measurement volume to approximately 50 microm. A new laser Doppler profile sensor is proposed, enabling determination of the velocity profile inside the measurement volume. Two fringe systems with contrary fringe spacing gradients are generated to determine the position as well as the velocity of passing tracer particles. Physically discriminating between the two measuring channels is done by a frequency-division-multiplexing technique with acousto-optic modulators. A frequency-doubled Nd:YAG laser and a fiber-optic measuring head were employed, resulting in a portable and flexible sensor. In the center of the measurement volume of approximately 1-mm length, a spatial resolution of approximately 5 microm was obtained. Spatially resolved measurements of the Blasius velocity profile are presented. Small velocities as low as 3 cm/s are measured. The sensor is applied in a wind tunnel to determine the wall shear stress of a boundary layer flow. All measurement results show good agreement with the theoretical prediction.     

High throughput assay of diffusion through Cx43 gap junction channels with a microfluidic chip

This paper describes a microfluidic-based assay capable of measuring gap-junction mediated dye diffusion in cultured cells. The technique exploits multistream laminar flow to selectively expose cells to different environments, enabling continuous loading of cells in one compartment while monitoring, in real time, dye diffusion into cells of a neighboring compartment. A simple one-dimensional diffusion model fit to the data extracted the diffusion coefficient of four different dyes, 5-(6)-carboxyfluorescein, 5-chloromethylfluorescein, Oregon green 488 carboxylic acid, and calcein. Different inhibitors were assayed for their ability to reduce dye coupling. The chip can screen multiple inhibitors in parallel in the same cell preparation, demonstrating its potential for high throughput. The technique provides a convenient method to measure gap junction mediated diffusion and a screen for drugs that affect gap junction communication.     

Fiber-optic strain-displacement sensor employing nonlinear buckling

A new class of intrinsic fiber-optic strain-displacement sensors based on the precisely controlled nonlinear buckling of optical fibers and the resulting optical bend loss is introduced. A multimode fiber version of the sensor is described that exhibits a sensing range convenient for many structural monitoring applications (<100 nm to several millimeters), linear response over a wide range of displacements, and excellent repeatability. It is extremely simple to fabricate and employs inexpensive optoelectronics. A high-temperature version of the sensor is capable of operation at temperatures as high as 600 degrees C.     

Stability of Laminar and Turbulent Flow of Superfluid 4He at mK Temperatures Around an Oscillating Microsphere

The flow of superfluid helium around a vibrating microsphere is investigated at temperatures between 1 K and 25 mK. At small oscillation amplitudes pure potential flow is observed, the linear drag force on the sphere being determined only by ballistic quasiparticle scattering below 0.7 K with phonons contributing exclusively below 0.5 K. At larger oscillation amplitudes a strongly nonlinear drag force gives evidence of stable turbulent flow if at least 0.6 pW are transferred from the sphere to the turbulent superfluid. In an intermediate range of amplitudes (or driving forces) both flow patterns are unstable and intermittent switching between both is observed below 0.5 K. We have recorded time series of this switching phenomenon at constant drives and temperatures lasting up to 36 hours. We have made a statistical analysis of the times series by means of reliability theory. The lifetime of the turbulent phases grows with increasing drive and diverges at a critical value (or at least becomes unmeasurably long). Stability of the laminar phases in the intermediate regime depends on the excess velocity of the sphere above the critical velocity. Metastable laminar phases are observed above the critical velocity having a mean lifetime limited to 25 minutes by natural background radioactivity which occasionally produces local vorticity due to ionization of the liquid. Finally, it is suggested that the breakdown of potential flow belongs to the class of “system failure” experiments which is well known in reliability testing and whose statistical properties are described by extreme-value theory. PACS numbers: 67.40.Vs, 47.27.Cn.     

Counting signal processing and counting level normalization techniques of polarization-insensitive fiber-optic Michelson interferometric sensors

A counting signal processing technique of the fiber-optic interferometric sensor is proposed. The technique is capable of counting the numbers of the maximum and minimum of the output interferometric signal in a specific time duration, and it can be used as the basis to distinguish the sensing phase signal. It can also be used as a signal detector on applications such as intrusion detection. All sensors are subject to aging of the optical components and bending loss, and therefore the output signal of each sensor may vary with time. We propose a counting level normalization technique to compensate for these variations and to obtain the correct counting numbers.     

Conveying of Solid Particles in Newtonian and Non-Newtonian Carriers

This article deals with the effect of slurry composition and volumetric concentration on the flow behavior of slurries containing fine-grained and coarse-grained particles. Fluidic fly and bottom ash slurries and sand slurries were experimentally investigated. Kaolin slurries with and without a peptizing agent were used as the carrier liquid for the sand slurries to compare the effect of Newtonian and non-Newtonian carriers. The study revealed a time-dependent yield pseudo-plastic behavior of fluidic fly and fly/bottom ash slurries and the possibility of substantial reduction of the flow resistance by mechanical treatment or by the arrangement of particle size distribution. The flow behavior of fluidic ash slurries can be approximated by the Bulkley-Herschel model in the laminar region. In the turbulent region, the Wilson or Slatter models can be used. The effect of the size distribution of the sand slurry on the hydraulic gradient depends on the flow velocity. The coarse sand slurry reaches a higher hydraulic gradient than the fine sand slurry: the difference decreases with growing velocity. The highly concentrated sand-kaolin slurries show non-Newtonian behavior. When the carrier kaolin slurry is peptized, the hydraulic gradient in the laminar region becomes markedly lower, and the favorable effect vanishes in the transitional and turbulent regions. The addition of small amounts of kaolin favorably affects the flow behavior of the sand slurry.     

A theoretical and experimental analysis of the received signal fromdisturbed blood flow

A theoretical and experimental study of the received ultrasonic signal from calibrated stenotic flow phantoms is presented. A finite element analysis of the velocity profile for 30, 50, and 80% stenoses provides a basis for the study of the experimental results. High-resolution images of the returned signal obtained from a unique experimental system and a high volume concentration of scatterers are then presented. The authors show that in the presence of 30 and 50% stenoses, particularly for the low velocities which would be associated with diastole, the duration of the signal correlation increases in a region which is distal to the stenosis and near the vessel walls, rather than the expected decrease. This results from the decrease in the mean velocity and velocity spread within this region. In the presence of high velocities associated with systolic flow, the magnitude of the reverse flow component increases as does the peak velocity in the center of the vessel. These changes produce an increase in the radial velocity gradient, a shift in the gradient peak, and a decrease in the correlated signal interval in comparison with laminar flow. Thus, the spatial variation in the mean velocity and velocity gradient, and spatial variation in the signal correlation can be used to detect the change in the flow profile     

AN OPTICAL METHOD FOR CONTINUOUSLY MEASURING FLOW VELOCITY AND COMPOSITION OF A MIXTURE OF POWDERS

A new method for continuously measuring flow velocity and composition of a mixture of powders in solid mixing equipment is proposed in this paper. This method uses an optical technique combining the image sensor anemometer of reflected light system and an image fiber inserted directly into the flowing powders' bed. From experiments for demonstration of this method, it is found that the flow velocity and the composition of the powder mixture in the mixer can be measured accurately and with high precision by applying this method.     

Infrared single-mode fiber-optic Fourier-transform spectrometry and double Fourier interferometry

An infrared single-mode fiber-optic Fourier-transform spectrometer constructed for the demonstration of the technique is described, in which beam splitting and beam combining are performed with fiber-optic directional couplers and the optical path difference scan is generated by stretching fibers. Experiments done with this fiber-optic Fourier-transform spectrometer are presented. A spectral resolution of 1328 at 2.2 μm can be achieved. The experimental results show the feasibility of fiber-optic Fourier-transform spectrometry and double Fourier interferometry.     

Vorticity evolution mechanism in near‐field of a transverse jet

Abstract

Flow structure and vorticity evolution processes in the near field of an elevated jet in a crossflow are experimentally studied in a wind tunnel. The instantaneous and time‐averaged flow field characteristics are observed and measured by using a flow visualization technique and a high‐speed Particle Image Velocimeter (PIV). Time histories of the instantaneous velocity of the vortical flows in the shear‐layer are recorded by a hot‐wire anemometer and a high‐speed data acquisition system in order to analyze the frequency characteristics of the traveling coherent structure in the shear‐layer. Experiments are performed between two different jet‐to‐crossflow momentum flux ratios R = 0.08 and 0.56, which are selected from two regimes with different kinds of flow patterns at a fixed crossflow Reynolds number 2051. The behaviors and mechanisms of the vortical flow structure and the vorticity evolution mechanisms appear to be distinct in different flow regimes. By analyzing the pictures of the smoke flow visualization and the instantaneous vorticity contour maps, two kinds of vorticity evolution mechanisms, “shear‐induced vortices” and “swing‐induced vortices”, can be identified in the shear‐layer evolving from the jet exit. The time‐averaged velocity field and vorticity properties are also discussed in this paper.