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We investigate two-phase (oil and water) flow in head-on microfluidic devices, which consist of two identical channels as inlets and the “long leg” as a constriction channel leading to a wider outlet section. Over an exceptionally broad range of flow rates of 10-4–10 μl/min in 10–100 μm (hydraulic diameter) microchannels, corresponding to capillary numbers of 10-6–10-1, a two-phase flow map is presented. A rich flow behavior was found. The flow patterns observed were dripping, jetting, and threading. These phenomena are interpreted as caused by capillary instability, squeezing, and shearing by considering the contribution of different forces acting at the oil/water interface. This device provides us with a broad choice to generate droplets of different sizes and frequencies by modifying either the geometrical design or the flow rates. [ABSTRACT FROM AUTHOR]

The configurational entropy of interacting particles adsorbed on one-dimensional channels arranged in a triangular cross-sectional structure is studied by combining Monte Carlo simulation and thermodynamic integration method. Three different energies have been considered in the adsorption process: (1) εo, constant interaction energy between a monomer and an adsorption site; (2) wL, interaction energy between nearest-neighbor particles adsorbed along a single channel, and (3) wT, interaction energy between particles adsorbed across nearest-neighbor channels. Special attention is devoted to the case of repulsive transversal interactions (wT>0), for which a rich variety of ordered phases are observed in the adlayer, depending on the value of the parameters kBT/wT (being kB the Boltzmann constant) and wL/wT. The influence of each ordered structure on the configurational entropy of the adlayer has been analyzed and discussed in the context of the lattice-gas model. [ABSTRACT FROM AUTHOR]

In this work, we investigate the fully developed flow field of two vertically stratified fluids (one phase flowing above the other) in a curved channel of rectangular cross section. The domain perturbation technique is applied to obtain an analytical solution in the asymptotic limit of low Reynolds numbers and small curvature ratios (the ratio of the width of the channel to its radius of curvature). The accuracy of this solution is verified by comparison with numerical simulations of the nonlinear equations. The flow is characterized by helical vortices within each fluid, which are driven by centrifugal forces. The number of vortices and their direction of circulation varies with the parameters of the system (the volume fraction, viscosity ratio, and Reynolds numbers). We identify nine distinct flow patterns and organize the parameter space into corresponding flow regimes. We show that the fully developed interface between the fluids is not horizontal, in general, but is deformed by normal stresses associated with the circulatory flow. The results are especially significant for flows in microchannels, where the Reynolds numbers are small. Themathematical results in this paper include an analytical solution to two coupled biharmonic partial differential equations; these equations arise in two-phase, two-dimensional Stokes flows. [ABSTRACT FROM AUTHOR]

Passive particle focusing based on inertial microfluidics was recently introduced as a high-throughput alternative to active focusing methods that require an external force field to manipulate particles. In inertial microfluidics, dominant inertial forces cause particles to move across streamlines and occupy equilibrium positions along the faces of walls in flows through straight micro channels. In this study, we systematically analyzed the addition of secondary Dean forces by introducing curvature and show how randomly distributed particles entering a simple u-shaped curved channel are focused to a fixed lateral position exiting the curvature. We found the lateral particle focusing position to be fixed and largely independent of radius of curvature and whether particles entering the curvature are pre-focused (at equilibrium) or randomly distributed. Unlike focusing in straight channels, where focusing typically is limited to channel cross-sections in the range of particle size to create single focusing point, we report here particle focusing in a large cross-section area (channel aspect ratio 1:10). Furthermore, we describe a simple u-shaped curved channel, with single inlet and four outlets, for filtration applications. We demonstrate continuous focusing and filtration of 10 lm particles (with >90% filtration efficiency) from a suspension mixture at throughputs several orders of magnitude higher than flow through straight channels (volume flow rate of 4.25ml/min). Finally, as an example of high throughput cell processing application, white blood cells were continuously processed with a filtration efficiency of 78% with maintained high viability. We expect the study will aid in the fundamental understanding of flow through curved channels and open the door for the development of a whole set of bio-analytical applications. [ABSTRACT FROM AUTHOR]

A model for the underwater noise of whitecaps is presented and compared with the noise measured beneath plunging seawater laboratory waves. The noise from a few hundred hertz up to at least 80 kHz is assumed to be due to the pulses of sound radiated by bubbles formed within a breaking wave crest. The total noise level and its dependence on frequency are a function of bubble creation rate, bubble damping factor and an ‘acoustical skin depth’ associated with scattering and absorption by the bubble plume formed within the crest. Calculation of breaking wave noise is made using estimates of these factors, which are made independently of the noise itself. The results are in good agreement with wave noise measured in a laboratory flume when compensated for reverberation. A closed-form, analytical expression for the wave noise is presented, which shows a -11/6 power-law dependence of noise level on frequency, in good agreement with the -10/6 scaling law commonly observed in the open ocean. [ABSTRACT FROM AUTHOR]

A procedure is developed to detect the onset of interfacial instability in inclined film flows (with estimated accuracy better than 5%) and is used to show that the finite width of experimental channels stabilizes the undisturbed liquid film. Deviation from the classical prediction scales inversely with the product of channel width and sine of inclination angle, and for small inclinations and/or narrow channels is of the order of 100%. The effect is tentatively attributed to the influence of sidewalls on the traveling disturbances, which results in curved crestlines and transverse variation of wave characteristics. [ABSTRACT FROM AUTHOR]

Recent investigations by Monty et al. [J. Fluid Mech. 632, 431 (2009)] showed that important modal differences exist between channels/pipes and boundary layers, mainly in the largest energetic scales. In addition, Mathis et al. [J. Fluid Mech. 628, 311 (2009)] recently reported and quantified a nonlinear scale interaction in zero-pressure gradient turbulent boundary layers, whereby the large-scale motion amplitude modulates the small-scale motions. In this study, a comparison of this modulation effect of the streamwise velocity component is undertaken for all three flows for matched Reynolds number and measurement conditions. Despite the different large-scale phenomena in these internal and external wall-bounded flows, the results show that their amplitude modulation influence remains invariant in the inner region with some differences appearing in the outer region. [ABSTRACT FROM AUTHOR]

We have investigated shallow water flows through a channel with a contraction by experimental and theoretical means. The horizontal channel consists of a sluice gate and an upstream channel of constant width b0 ending in a linear contraction of minimum width bc. Experimentally, we observe upstream steady and moving bores/shocks, and oblique waves in the contraction, as single and multiple (steady) states, as well as a steady reservoir with a complex hydraulic jump in the contraction occurring in a small section of the bc/b0 and Froude number parameter plane. One-dimensional hydraulic theory provides a comprehensive leading-order approximation, in which a turbulent frictional parametrization is used to achieve quantitative agreement. An analytical and numerical analysis is given for two-dimensional supercritical shallow water flows. It shows that the one-dimensional hydraulic analysis for inviscid flows away from hydraulic jumps holds surprisingly well, even though the two-dimensional oblique hydraulic jump patterns can show large variations across the contraction channel. [ABSTRACT FROM AUTHOR]

Liquid/gas flows are experimentally investigated in 200 and 525 μm square microchannels made of glass and silicon. Liquid and gas are mixed in a cross-shaped section in a way to produce steady and homogeneous flows of monodisperse bubbles. Two-phase flow map and transition lines between flow regimes are examined. Bubble velocity and slip ratio between liquid and gas are measured. Flow patterns and their characteristics are discussed. Local and global dry out of the channel walls by moving bubbles in square capillaries are investigated as a function of the flow characteristics for partially wetting channels. Two-phase flow pressure drop is measured and compared to single liquid flow pressure drop. Taking into account the homogeneous liquid fraction along the channel, an expression for the two-phase hydraulic resistance is experimentally developed over the range of liquid and gas flow rates investigated. [ABSTRACT FROM AUTHOR]

The shallow water acoustic communication channel is characterized by strong signal degradation caused by multipath propagation and high spatial and temporal variability of the channel conditions. At the receiver, multipath propagation causes intersymbol interference and is considered the most important of the channel distortions. This paper examines the application of time-reversal acoustic (TRA) arrays, i.e., phase-conjugated arrays (PCAs), that generate a spatio-temporal focus of acoustic energy at the receiver location, eliminating distortions introduced by channel propagation. This technique is self-adaptive and automatically compensates for environmental effects and array imperfections without the need to explicitly characterize the environment. An attempt is made to characterize the influences of a PCA design on its focusing properties with particular attention given to applications in noncoherent underwater acoustic communication systems. Due to the PCA spatial diversity focusing properties, PC arrays may have an important role in an acoustic local area network. Each array is able to simultaneously transmit different messages that will focus only at the destination receiver node. [ABSTRACT FROM AUTHOR]

This paper aims to provide deeper insight into the suddenly contracted channel flow. The channels under investigation have a width of 18D, where D represents the channel height upstream of the step plane, and two contraction ratios: C=2 and 4. In the present three-dimensional finite volume analysis, the advective fluxes are discretized using an upwind scheme that provides a third-order accurate solution in uniform grid cases. For efficient calculation of field variables, working equations are solved separately based on the semi-implicit velocity-pressure coupling procedures. We exploit a theoretically appealing topological theory to determine lines of separation and reattachment, from which the pitchfork bifurcation flow can be identified in the contraction channel. To further elucidate the vortical details of the channel flow, we trace massless particles seeded in the flow, showing the spanwise spiraling flow motion. Emphasis is placed on flow phenomena in the upstream salient corner eddy and downstream tip corner eddy. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The influence of temperature-dependent viscosity on the flow along a channel with porous walls at different temperatures was analyzed. Numerical schemes were developed to solve the Navier–Stokes equation and the energy equation, coupled through the dependence of viscosity on temperature. Bifurcation diagrams are presented. Local analysis of the behavior of these bifurcations was also performed. The temporal and spatial stability of stationary solutions was studied by solving eigenvalue problems. The parameter space was explored and the regions where different stationary and periodic solutions appear are described. Periodic solutions obtained by solving the time-dependent problem are also presented. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present an extension of the existing continuum theory for sound wave propagation in dilute gases in “narrow” two-dimensional channels to arbitrary Knudsen numbers; the theory provides predictions for the wavelength and attenuation coefficient as a function of the oscillation frequency. A channel is considered narrow in the context of wave propagation when its height is much smaller than the characteristic diffusion length based on the wave frequency. This criterion is easily satisfied by small scale (transition-regime) channels for most frequencies of interest. Numerical simulations for a dilute monoatomic gas using the direct simulation Monte Carlo are used to verify the theoretical results. Good agreement is found between theory and simulation. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a numerical study of the two-dimensional solitary waves generated by a submerged body moving near the critical speed in a shallow water channel. Governing equations; Boundary conditions; Discretization and solution procedure; Validation; Variation of the submergence depth.

The changes in the configuration of a FENE bead-spring chain in a direct numerical simulation of turbulent channel flow and in some simple rheological flows are examined. Unraveling occurs both in uniaxial and shear flows, but the uniaxial flow is more effective. A vortex with a large rotation rate perpendicular to the principal strain of a uniaxial flow has only a minor retarding effect while a small rotation rate delays the unraveling substantially. In a turbulent flow, the chain unravels the most in the viscous sublayer, to about 90% of its fully extended length. It aligns at a 7° angle with the direction of mean flow. In the buffer zone, it unravels and coils up and takes different orientations at different times. Outside the wall region, the chain assumes a coiled configuration. The unraveling of the chain strongly depends on the relaxation time of the chain normalized with the wall shear rate, λ+. A value of λ+=10 exhibits strong unraveling while very weak unraveling is observed below λ+=1. [ABSTRACT FROM AUTHOR]

A steady, inviscid, incompressible, two-dimensional flow in a channel containing a vortex patch bounded by a vortex sheet is calculated numerically. The results cover a wide range of the channel width and the value of the jump in Bernoulli’s constant across the vortex sheet. An asymptotic theory is used to check the results for very narrow channels. A comparison with the solutions of the Navier–Stokes equations around an infinite array of circular cylinders [Fornberg, J. Fluid Mech. 225, 655 (1991)] is performed to check if the present flow can be used as a model for the wake. [ABSTRACT FROM AUTHOR]

Pneumatic actuation with multilayer soft lithography enables operation of up to thousands of valves in parallel using far fewer control lines. However, it is dependent on macroscopic switches and external pressure sources that require interconnects and limit portability. The authors present a more portable and multiplexed valve actuation strategy that uses a grid of mechanically actuated Braille pins to hydraulically, rather than pneumatically, deform elastic actuation channels that act as valves. Experimental and theoretical analyses show that the key to reliable operation of the hydraulic system is the use of nonvolatile ionic liquids as the hydraulic fluid. [ABSTRACT FROM AUTHOR]

This paper examines the rising motion of a layer of gas bubbles next to a vertical wall in a liquid in the presence of an upward flow parallel to the wall to help with the understanding of the fluid dynamics in a bubbly upflow in vertical channels. Only the region near the wall is simulated with an average pressure gradient applied to the domain that balances the weight of the liquid phase. The upward flow is created by the rising motion of the bubbles. The bubbles are kept near the wall by the lateral lift force acting on them as a result of rising in the shear layer near the wall. The rise velocity of the bubbles sliding on the wall and the average rise velocity of the liquid depend on three dimensionless parameters, Archimedes number, Ar, Eötvös number, Eo, and the average volume fraction of bubbles on the wall. In the limit of small Eo, bubbles are nearly spherical and the dependency on Eo becomes negligible. In this limit, the scaling of the liquid Reynolds number with Archimedes number and the void fraction is presented. A scaling argument is presented based on viscous dissipation analysis that matches the numerical findings. Viscous dissipation rates are found to be high in a thin film region between the bubble and the wall. A scaling of the viscous dissipation and steady state film thickness between the bubble and the wall with Archimedes number is presented. [ABSTRACT FROM AUTHOR]

Linear water wave theory suggests that wave patterns caused by a steadily moving disturbance are contained within a wedge whose half-angle depends on the depth-based Froude number FH. For the problem of flow past an axisymmetric pressure distribution in a finite-depth channel, we report on the apparent angle of the wake, which is the angle of maximum peaks. For moderately deep channels, the dependence of the apparent wake angle on the Froude number is very different to the wedge angle and varies smoothly as FH passes through the critical value FH = 1. For shallow water, the two angles tend to follow each other more closely, which leads to very large apparent wake angles for certain regimes. [ABSTRACT FROM AUTHOR]

Flow-noise resulting from oceanic turbulence and interactions with pressure-sensitive transducers can interfere with ambient noise measurements. This noise source is particularly important in low-frequency measurements (f<100 Hz) and in highly turbulent environments such as tidal channels. This work presents measurements made in the Chacao Channel, Chile, and in Admiralty Inlet, Puget Sound, WA. In both environments, peak currents exceed 3 m/s and pressure spectral densities attributed to flow-noise are observed at frequencies up to 500 Hz. At 20Hz, flow-noise exceeds mean slack noise levels by more than 50 dB. Two semi-empirical flow-noise models are developed and applied to predict flow-noise at frequencies from 20 to 500 Hz using measurements of current velocity and turbulence. The first model directly applies mean velocity and turbulence spectra while the second model relies on scaling arguments that relate turbulent dissipation to the mean velocity. Both models, based on prior formulations for infrasonic (f<20Hz) flow-noise, agree well with observations in Chacao Channel. In Admiralty Inlet, good agreement is shown only with the model that applies mean velocity and turbulence spectra, as the measured turbulence violates the scaling assumption in the second model. [ABSTRACT FROM AUTHOR]

Turbulent flows over a wavy wall are investigated in channels with a wavy bottom and a flat top with different channel heights. Flow structures are determined from proper orthogonal decompositions of velocity fields measured with particle image velocimetry. Three different channel heights are considered, which are characterized by blockage ratios β (half channel height to wave amplitude ratio) 3.3, 6.7, and 10. Measurements are evaluated at comparable Reynolds numbers (Re) around 10 000. Structural similarity of large-scale structures, which is valid at β = 6.7 and 10, no longer holds at β = 3.3. Furthermore, characteristic regions of flows over wavy walls exhibit different locations in the case of the smallest channel height. [ABSTRACT FROM AUTHOR]

Low probability of detection (LPD) communications are conducted at a low received signal-to-noise ratio (SNR) to deter eavesdroppers to sense the presence of the transmitted signal. Successful detection at intended receiver heavily relies on the processing gain achieved by employing the direct-sequence spread-spectrum (DSSS) technique. For scenarios that lack a sufficiently low SNR to maintain LPD, another metric, referred to as low probability of interception (LPI), is of interest to protect the privacy of the transmitted information. If covert communications take place in underwater acoustic (UWA) environments, then additional challenges are present. The time-varying nature of the UWA channel prevents the employment of a long spreading waveform. Furthermore, UWA environments are frequency-selective channels with long memory, which imposes challenges to the design of the spreading waveform. In this paper, a covert UWA communication system that adopts the DSSS technique and a coherent RAKE receiver is investigated. Emphasis is placed on the design of a spreading waveform that not only accounts for the transceiver structure and frequency-selective nature of the UWA channel, but also possesses a superior LPI. The proposed techniques are evaluated using both simulated and SPACE'08 in-water experimental data. [ABSTRACT FROM AUTHOR]

This paper proposes a single carrier (SC) receiver scheme with bandwidth-efficient frequency-domain equalization (FDE) for underwater acoustic (UWA) communications employing multiple transducers and multiple hydrophones. Different from the FDE methods that perform FDE on a whole data block, the proposed algorithm implements an overlapped-window FDE by partitioning a large block into small subblocks. A decision-directed channel estimation scheme is incorporated with the overlapped-window FDE to track channel variations and improve the error performance. The proposed algorithm significantly increases the length of each block and keeps the same number of training symbols per block, hence achieving better data efficiency without performance degradation. The proposed scheme is tested by the undersea data collected in the Rescheduled Acoustic Communications Experiment (RACE) in March 2008. Without coding, the 2-by-12 MIMO overlapped-window FDE reduces the average bit error rate (BER) over traditional SC-FDE schemes by 74.4% and 84.6% for the 400 m and 1000 m range systems, respectively, at the same data efficiency. If the same BER performance is required, the proposed algorithm has only 8.4% transmission overhead, comparing to over 20% overhead in other existing UWA OFDM and SC-FDE systems. The improved data efficiency and/or error performance of the proposed FDE scheme is achieved by slightly increased computational complexity over traditional SC-FDE schemes. [ABSTRACT FROM AUTHOR]

We present a microfluidic parallel circuit that directly compares the test channel of an unknown hydraulic resistance with the reference channel with a known resistance, thereby measuring the unknown resistance without any measurement setup, such as standard pressure gauges. Many of microfluidic applications require the precise transport of fluid along a channel network with complex patterns. Therefore, it is important to accurately characterize and measure the hydraulic resistance of each channel segment, and determines whether the device principle works well. However, there is no fluidic device that includes features, such as the ability to diagnose microfluidic problems by measuring the hydraulic resistance of a microfluidic component in microscales. To address the above need, we demonstrate a simple strategy to measure an unknown hydraulic resistance, by characterizing the hydraulic resistance of microchannels with different widths and defining an equivalent linear channel of a microchannel with repeated patterns of a sudden contraction and expansion. [ABSTRACT FROM AUTHOR]

Depth evolution and final deposits play a crucial role in the description of the dynamics of granular avalanches. This paper presents new and important results on the geometric deformation and measurements of avalanche depositions in laboratory granular flows and their comparisons with theoretical predictions through some benchmark problems for flows down curved and twisted channels merging into a horizontal plane. XY-table and analoglaser sensor are applied to measure geometries of deposited masses in the fanlike open transition and runout zones for different granular materials, different channel lengths, and different channel mouths in the runout zone. The model equations proposed by Pudasaini and Hutter [“Rapid shear flows of dry granular masses down curved and twisted channels,” J. Fluid Mech. 495, 193 (2003)] are used for theoretical prediction. We show that geometric parameters such as curvature, twist and local details of the channel play a crucial role in the description of avalanching debris and their deposits in the standstill. Asymmetric depositions and surface contours about the central line of the channel could not be produced and predicted by any other classical theories and available experiments in the literature as done in this paper. Such a role played by the geometrical parameters of the channel over physical parameters for the flow of granular materials down a general channel was not investigated before. It is demonstrated that the numerical simulations of the model equations and experimental observations are generally in good agreement. [ABSTRACT FROM AUTHOR]

Direct numerical simulation is used to investigate the nature of pressure fluctuations induced by surface roughness in a turbulent channel flow at Reτ=400 for three-dimensional periodic roughness elements, whose peaks overlap approximately 25% of the logarithmic layer. The three-dimensional roughness elements alter the pressure statistics significantly, compared to the corresponding smooth-wall flow, in both the inner and outer (core) regions of the channel. The direct consequence of roughness is an increased form drag, associated with more intense pressure fluctuations. However, it also alters the pressure fluctuations in the outer layer of the flow, and modifies the length scales defined by two-point correlations. We also find that the depth of the roughness sublayer defined by the pressure fluctuations is very different from that given by the large- and small-scale statistics from the velocity field. [ABSTRACT FROM AUTHOR]

In the present paper, a steady subsonic gas flow either in a circular micropipe or in a planar microchannel driven by pressure within the slip flow regime is studied theoretically by using a perturbation expansion method to solve compressible Navier-Stokes equations. The isothermal flow assumption used in previous theoretical studies is given up. High-order boundary conditions of velocity slip and temperature jump are adopted at the wall. The set of dimensionless governing equations with two small similarity parameters, namely, the ratio of height to length [variant_greek_epsilon], and the Knudsen number Kn, is approximated successively by using the perturbation expansions. The various cases such as [variant_greek_epsilon]«Kn2, [variant_greek_epsilon]∼Kn2, and [variant_greek_epsilon]∼Kn1.5 are studied in detail. Explicit analytical solutions for pressure, density, velocity, temperature, and mass flow rate are obtained up to order of O(Kn2). It is shown that the solution formulas for long channels ([variant_greek_epsilon]«Kn2) in lower order are in exact agreement with previous theoretical results. In particular, it is proved that the isothermal flow assumption is indeed reliable for relatively lower-order expansions. However, for higher-order expansions, the flow cannot be considered as isothermal, and the higher-order temperature correction is also given. The present high-order perturbation solutions can be applied even to a relatively shorter channel, and the results agree very well with those by the direct simulation Monte Carlo approach. [ABSTRACT FROM AUTHOR]

The results of numerous studies performed to date have shown that the performance of various hydraulic systems can be significantly improved by using curved conduit geometries instead of straight tubes. In particular, the formation of Dean vortices, which enhance the development of centrifugal instabilities, has been identified as a factor behind reducing the near-wall concentration buildup in particulate flow devices (e.g., in membrane filtration modules). Still, several issues regarding the effect of conduit curvature on local multidimensional phenomena governing fluid flow still remain open. A related issue is concerned with the impact that conduit geometry makes on the concentration distribution of a dispersed phase in two-phase flows in general, and in particulate flows (solid/liquid or solid/gas suspensions) in particular. It turns out that only very limited efforts have been made in the past to understand the fluid mechanics of such flows via advanced computer simulations. The purpose of this paper is to present the results of full three-dimensional (3D) theoretical and numerical analyses of single- and two-phase dilute particle/liquid flows in U-bend and helical curved conduits. The numerical analysis is based on computational fluid dynamics (CFD) simulations performed using a state-of-the-art multiphase flow computer code, NPHASE. The major issues discussed in the first part of the paper are concerned with the effect of curved/coiled geometry on the evolution of flow field and the associated wall shear. It has been demonstrated that the primary curvature (a common factor for both the U-bend and helix geometries) may cause a substantial asymmetry in the radial distribution of the main flow velocity. This, in turn, leads to a significant, albeit highly nonuniform, increase in the wall shear stress. Specifically, the wall shear around the outer half of tube circumference may become twice the corresponding value for a straight tube, and gradually decrease to the straight tube level when approaching the inner bend location. Another important issue is concerned with the effect of the length of the curved section and of the straight tube just upstream of the bend. Specifically, the discontinuity in curvature at the straight-to-curved transition location results in a localized change in the wall shear distribution around the tube circumference. On the other hand, if the curved tube is sufficiently long, such as in the case of a helix, the asymmetric velocity profile eventually reaches a fully developed pattern. The effect of nondimensional flow parameters, the Reynolds and Dean numbers, on the entry length along the curved helix geometry is also investigated in this paper. It is shown that the predicted developing length agrees well with the existing experimental data. The objective of the second part of the paper is to investigate the mutual interactions between the liquid flow and solid particles in particulate two-phase flows in both the U-bend and helical geometries. It is shown that particle inertia causes an increase in the wall shear. At the same time, two interesting aspects are shown of Dean vortices on particle concentration under the effect of gravity. One of them is the shift in the particle settling zone from the bottom of the horizontal (or nearly horizontal) tube toward the inner bend of the tube. The other, even more important, is a dramatic reduction in peak concentration with increasing Dean number. Both effects are important for equipment design and optimization in biotechnology and process industries. [ABSTRACT FROM AUTHOR]

Wave scattering over a sinusoidal bottom in the presence of an ambient current is investigated experimentally. Waves were generated in a flume with and without current and propagated over a patch of four sinusoidal bars before dissipating on a beach. A Doppler shift of the resonant Bragg frequency and an amplification of the wave reflection are observed in the presence of the current. Weak reflections over the beach are found to have a significant influence on the wave reflection over the bars. [ABSTRACT FROM AUTHOR]

Roughness features on the walls of a channel wall affect the pressure drop of a fluid flowing through that channel. This roughness effect can be described by (i) flow area constriction and (ii) increase in the wall shear stress. Replotting the Moody’s friction factor chart with the constricted flow diameter results in a simplified plot and yields a single asymptotic value of friction factor for relative roughness values of [variant_greek_epsilon]/D>0.03 in the fully developed turbulent region. After reviewing the literature, three new roughness parameters are proposed (maximum profile peak height Rp, mean spacing of profile irregularities RSm, and floor distance to mean line Fp). Three additional parameters are presented to consider the localized hydraulic diameter variation (maximum, minimum, and average) in future work. The roughness [variant_greek_epsilon] is then defined as Rp+Fp. This definition yields the same value of roughness as obtained from the sand-grain roughness [H. Darcy, Recherches Experimentales Relatives au Mouvement de L’Eau dans les Tuyaux (Mallet-Bachelier, Paris, France, 1857); J. T. Fanning, A Practical Treatise on Hydraulic and Water Supply Engineering (Van Nostrand, New York, 1877, revised ed. 1886); J. Nikuradse, “Laws of flow in rough pipes” [“Stromungsgesetze in Rauen Rohren,” VDI-Forschungsheft 361 (1933)]; Beilage zu “Forschung auf dem Gebiete des Ingenieurwesens,” Ausgabe B Band 4, English translation NACA Tech. Mem. 1292 (1937)]. Specific experiments are conducted using parallel sawtooth ridge elements, placed normal to the flow direction, in aligned and offset configurations in a 10.03 mm wide rectangular channel with variable gap (resulting hydraulic diameters of 325 μm–1819 μm with Reynolds numbers ranging from 200 to 7200 for air and 200 to 5700 for water). The use of constricted flow diameter extends the applicability of the laminar friction factor equations to relative roughness values (sawtooth height) up to 14%. In the turbulent region, the aligned and offset roughness arrangements yield different results indicating a need to further characterize the surface features. The laminar to turbulent transition is also seen to occur at lower Reynolds numbers with an increase in the relative roughness. [ABSTRACT FROM AUTHOR]

It is generally accepted that in simple microchannel flows the electrical double layer at walls is thin enough for "slip velocity" boundary conditions to be used with good approximation. Recent theoretical work by one of the authors has considered the limits of this approach in cases characterized by nonuniform liquid properties and complex channel geometries. In that work, the chemically reacting flow in an arbitrary channel geometry produced by electric potential and pressure differences with heat transfer and electrophoresis is considered. The present work undertakes a broad test of the model approach in a complex channel network geometry, in the case of nonreacting uniform-property liquid. Velocity is measured by particle tracking with correction for electrophoretic motion. Measured and predicted velocities in a three-dimensional experimental T-junction within a network of five channel segments are compared for three cases of steady flow including electrically driven flow, pressure-driven flow, and mixed pressure and electrical flow. All conditions of the experiment required to determine the flow uniquely have been measured. The computational methodology used combines local three-dimensional representation with overall circuit analysis of the channel network. Comparisons are found to be within the 5% experimental scatter of the velocity measurement method used. The work emphasizes the care required in fabrication, measurement, flow control, and numerical solution if prediction of actual fabricated devices is to be achieved. [ABSTRACT FROM AUTHOR]

We have investigated device performance for In0.7Ga0.3As and In0.53Ga0.47As metal-oxide-semiconductor transistors (MOSFETs) with and without InP barrier layer using atomic layer deposited Al2O3 gate dielectric. InP barrier layer was found to provide higher transconductance for both In0.7Ga0.3As and In0.53Ga0.47As MOSFETs, especially for In0.7Ga0.3As. In0.7Ga0.3As MOSFETs with InP barrier layer show much higher transconductance and lower subthreshold swing than other MOSFETs studied. These In0.7Ga0.3As MOSFETs exhibit high drive current of 98 mA/mm (L=20 μm), subthreshold swing of 106 mV/decade and maximum effective channel mobility of 4402 cm2/V s. [ABSTRACT FROM AUTHOR]

The performance and economics of turbines in a tidal array are largely dependent on the power per turbine, and so, approaches that can increase this power are crucial for the development of tidal energy. In this paper, we combine a two-scale partial array model and a one-dimensional channel model to investigate the effects of blockage, turbine arrangement, and channel dynamics on tidal turbines. The power per turbine is obtained as the product of two parameters: a power coefficient measuring the power acquired from the instantaneous flow and an environment coefficient showing the response of the channel to added drag. The results suggest that taking account of channel dynamics will decrease the predicted power and the optimal induction factor. The model also shows that when the number of turbines in a row is increased, the power per turbine may monotonically increase or decrease or attain a maximum value at a certain global blockage. These different results depend on two characteristic parameters of the channel: α and λD. Furthermore, we find that besides turbine density (blockage), the arrangement of the turbines should also be considered if we want to obtain an efficient array. Appropriate arrangements can enhance the performance of turbines in tidal channels although the beneficial effects will be partly offset by reduced velocities. The turbine arrangement also has an effect on the optimal global blockage at which the power attains its maximum value. As the rate of increase of the power per turbine from an array spanning the whole channel width to the optimal partial array diminishes with increasing blockage, the optimal global blockage will also decrease. [ABSTRACT FROM AUTHOR]