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Showing papers on "Fluid dynamics published in 2002"


Journal ArticleDOI
TL;DR: In this article, two computer codes, TOUGH2 and FLAC3D, are linked and jointly executed for coupled thermal-hydrologic-mechanical (THM) analysis of multiphase fluid flow, heat transfer, and deformation in fractured and porous rock.

771 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present a simulation of the transition and free-molecular regime of pressure-driven liquid flow in a shear-driven and separated liquid flow model.
Abstract: Basic Concepts and Technologies * Governing Equations and Slip Models * Shear-Driven and Separated Micro Flows * Pressure-Driven Micro Flows: Slip Flow Regime * Pressure-Driven Flows: Transition and Free- Molecular Regimes * Thermal Effects in Micro Scales * Prototype Applications of Gas Micro Flows * Electrokinetically-Driven Liquid Micro Flows * Numerical Methods for Continuous Simulation * Numerical Methods for Atomistic Simulation

612 citations


Journal ArticleDOI
TL;DR: The critical shear stress and shear rate to observe deviations from predictions using the no-slip boundary condition increased nearly exponentially with increasing roughness and diverged at approximately 6 nm rms roughness.
Abstract: A controversial point in fluid dynamics is to distinguish the relative importance of surface roughness and fluid-surface intermolecular interactions in determining the boundary condition. Here hydrodynamic forces were compared for flow of Newtonian fluids past surfaces of variable roughness but similar, poorly wetted, surface chemistry. The critical shear stress and shear rate to observe deviations from predictions using the no-slip boundary condition increased nearly exponentially with increasing roughness and diverged at $\ensuremath{\approx}6$ nm rms roughness. We conclude that local intermolecular interactions dominated when the surface was very smooth, but roughness dominated otherwise. This quantifies the limits of both ideas.

568 citations


Journal ArticleDOI
TL;DR: This work proves existence of weak solutions and gives a complete analysis of a finite element scheme which allows a simulation of the coupled problem to be uncoupled into steps involving porous media and fluid flow subproblems.
Abstract: The transport of substances back and forth between surface water and groundwater is a very serious problem. We study herein the mathematical model of this setting consisting of the Stokes equations in the fluid region coupled with the Darcy equations in the porous medium, coupled across the interface by the Beavers--Joseph--Saffman conditions. We prove existence of weak solutions and give a complete analysis of a finite element scheme which allows a simulation of the coupled problem to be uncoupled into steps involving porous media and fluid flow subproblems. This is important because there are many "legacy" codes available which have been optimized for uncoupled porous media and fluid flow.

552 citations


Book
12 Aug 2002
TL;DR: In this article, the authors discuss the fluid-dynamic type equations derived from the Boltzmann equation as its asymptotic behavior for small mean free path and the boundary conditions that describe the behavior of the gas in the continuum limit.
Abstract: In this series of talks, I will discuss the fluid-dynamic-type equations that is derived from the Boltzmann equation as its the asymptotic behavior for small mean free path. The study of the relation of the two systems describing the behavior of a gas, the fluid-dynamic system and the Boltzmann system, has a long history and many works have been done. The Hilbert expansion and the Chapman–Enskog expansion are well-known among them. The behavior of a gas in the continuum limit, however, is not so simple as is widely discussed by superficial understanding of these solutions. The correct behavior has to be investigated by classifying the physical situations. The results are largely different depending on the situations. There is an important class of problems for which neither the Euler equations nor the Navier–Stokes give the correct answer. In these two expansions themselves, an initialor boundaryvalue problem is not taken into account. We will discuss the fluid-dynamic-type equations together with the boundary conditions that describe the behavior of the gas in the continuum limit by appropriately classifying the physical situations and taking the boundary condition into account. Here the result for the time-independent case is summarized. The time-dependent case will also be mentioned in the talk. The velocity distribution function approaches a Maxwellian fe, whose parameters depend on the position in the gas, in the continuum limit. The fluid-dynamictype equations that determine the macroscopic variables in the limit differ considerably depending on the character of the Maxwellian. The systems are classified by the size of |fe− fe0|/fe0, where fe0 is the stationary Maxwellian with the representative density and temperature in the gas. (1) |fe − fe0|/fe0 = O(Kn) (Kn : Knudsen number, i.e., Kn = `/L; ` : the reference mean free path. L : the reference length of the system) : S system (the incompressible Navier–Stokes set with the energy equation modified). (1a) |fe − fe0|/fe0 = o(Kn) : Linear system (the Stokes set). (2) |fe − fe0|/fe0 = O(1) with | ∫ ξifedξ|/ ∫ |ξi|fedξ = O(Kn) (ξi : the molecular velocity) : SB system [the temperature T and density ρ in the continuum limit are determined together with the flow velocity vi of the first order of Kn amplified by 1/Kn (the ghost effect), and the thermal stress of the order of (Kn) must be retained in the equations (non-Navier–Stokes effect). The thermal creep[1] in the boundary condition must be taken into account. (3) |fe − fe0|/fe0 = O(1) with | ∫ ξifedξ|/ ∫ |ξi|fedξ = O(1) : E+VB system (the Euler and viscous boundary-layer sets). E system (Euler set) in the case where the boundary is an interface of the gas and its condensed phase. The fluid-dynamic systems are classified in terms of the macroscopic parameters that appear in the boundary condition. Let Tw and δTw be, respectively, the characteristic values of the temperature and its variation of the boundary. Then, the fluid-dynamic systems mentioned above are classified with the nondimensional temperature variation δTw/Tw and Reynolds number Re as shown in Fig. 1. In the region SB, the classical gas dynamics is inapplicable, that is, neither the Euler

501 citations


01 Jan 2002
TL;DR: In this article, the authors discuss the fluid-dynamic type equations derived from the Boltzmann equation as its asymptotic behavior for small mean free path and the boundary conditions that describe the behavior of the gas in the continuum limit.
Abstract: In this series of talks, I will discuss the fluid-dynamic-type equations that is derived from the Boltzmann equation as its the asymptotic behavior for small mean free path. The study of the relation of the two systems describing the behavior of a gas, the fluid-dynamic system and the Boltzmann system, has a long history and many works have been done. The Hilbert expansion and the Chapman–Enskog expansion are well-known among them. The behavior of a gas in the continuum limit, however, is not so simple as is widely discussed by superficial understanding of these solutions. The correct behavior has to be investigated by classifying the physical situations. The results are largely different depending on the situations. There is an important class of problems for which neither the Euler equations nor the Navier–Stokes give the correct answer. In these two expansions themselves, an initialor boundaryvalue problem is not taken into account. We will discuss the fluid-dynamic-type equations together with the boundary conditions that describe the behavior of the gas in the continuum limit by appropriately classifying the physical situations and taking the boundary condition into account. Here the result for the time-independent case is summarized. The time-dependent case will also be mentioned in the talk. The velocity distribution function approaches a Maxwellian fe, whose parameters depend on the position in the gas, in the continuum limit. The fluid-dynamictype equations that determine the macroscopic variables in the limit differ considerably depending on the character of the Maxwellian. The systems are classified by the size of |fe− fe0|/fe0, where fe0 is the stationary Maxwellian with the representative density and temperature in the gas. (1) |fe − fe0|/fe0 = O(Kn) (Kn : Knudsen number, i.e., Kn = `/L; ` : the reference mean free path. L : the reference length of the system) : S system (the incompressible Navier–Stokes set with the energy equation modified). (1a) |fe − fe0|/fe0 = o(Kn) : Linear system (the Stokes set). (2) |fe − fe0|/fe0 = O(1) with | ∫ ξifedξ|/ ∫ |ξi|fedξ = O(Kn) (ξi : the molecular velocity) : SB system [the temperature T and density ρ in the continuum limit are determined together with the flow velocity vi of the first order of Kn amplified by 1/Kn (the ghost effect), and the thermal stress of the order of (Kn) must be retained in the equations (non-Navier–Stokes effect). The thermal creep[1] in the boundary condition must be taken into account. (3) |fe − fe0|/fe0 = O(1) with | ∫ ξifedξ|/ ∫ |ξi|fedξ = O(1) : E+VB system (the Euler and viscous boundary-layer sets). E system (Euler set) in the case where the boundary is an interface of the gas and its condensed phase. The fluid-dynamic systems are classified in terms of the macroscopic parameters that appear in the boundary condition. Let Tw and δTw be, respectively, the characteristic values of the temperature and its variation of the boundary. Then, the fluid-dynamic systems mentioned above are classified with the nondimensional temperature variation δTw/Tw and Reynolds number Re as shown in Fig. 1. In the region SB, the classical gas dynamics is inapplicable, that is, neither the Euler

501 citations


Patent
05 Sep 2002
TL;DR: In this article, a fluid from a fluid source, a surgical device which provides energy and the fluid to the tissue, and a control mechanism which changes a flow rate of fluid provided from the surgical device and changes a rate of energy provided by the surgeon.
Abstract: Medical devices, methods and systems for treating tissue are provided. An exemplary system comprises a fluid from a fluid source, a surgical device which provides energy and the fluid to the tissue and a control mechanism which changes a flow rate of fluid provided from the surgical device and changes a rate of energy provided from the surgical device. The fluid flow rate changes between at least two non-zero flow rates and the energy rate changes between at least two non-zero energy rates. An exemplary method comprises providing a fluid from a fluid source, providing a surgical device which provides energy and the fluid to the tissue, and changing a flow rate of fluid provided from the surgical device with a change in a rate of energy provided from the surgical device. Exemplary devices comprise a tip portion configured to provide energy and a fluid to a tissue.

465 citations


Journal ArticleDOI
TL;DR: In this paper, a finite element analysis, employing a specialised computational fluid dynamics package, is used to simulate the fluid flow, and thus dispersion of reinforcement material in a molten matrix alloy during stirring.

454 citations


Journal ArticleDOI
TL;DR: In this paper, the authors considered a capacitvely coupled radio frequency discharge plasma generator, where the plasma is generated on the surface of a dielectric circuit board with electrode strips on the top and bottom.
Abstract: Modeling of fluid dynamics and the associated heat transfer induced by plasma between two parallel electrodes is investigated. In particular, we consider a capacitvely coupled radio frequency discharge plasma generator, where the plasma is generated on the surface of a dielectric circuit board with electrode strips on the top and bottom. The electrodes have a thickness of 100 μm, which is comparable to the height of the boundary layer. The regime considered is that the electron component is in the non-equilibrium state, and the plasma is nonthermal. Overall, due to the ion and large fluid particle interaction, the pressure is higher in the downstream of the electrode, causing the velocity structure to resemble that of a wall jet. Parameters related to the electrode operation, including the voltage, frequency, and free stream speed are varied to investigate the characteristics of the plasma-induced flow. Consistent with the experimental observation, the model shows a clear dependence of the induced jet velocity on the applied voltage and frequency. The heat flux exhibited a similar dependence on the strength of the plasma. The present plasma-induced flow concept can be useful for thermal management and active flow control.

436 citations


Journal ArticleDOI
TL;DR: Experimental observations of the fluid flow profile obtained by superimposing images of particle movement in a plane normal to the electrode surface are presented and good agreement is found between the numerical and experimental streamlines.
Abstract: The application of a nonuniform ac electric field to an electrolyte using coplanar microelectrodes results in steady fluid flow. The flow has its origin in the interaction of the tangential component of the nonuniform field with the induced charge in the electrical double layer on the electrode surfaces. Termed ac electro-osmosis, the flow has been studied experimentally and theoretically using linear analysis. This paper presents experimental observations of the fluid flow profile obtained by superimposing images of particle movement in a plane normal to the electrode surface. These experimental streamlines demonstrate that the fluid flow is driven at the surface of the electrodes. Experimental measurements of the impedance of the electrical double layer on the electrodes are also presented. The potential drop across the double layer at the surface of the electrodes is calculated numerically using a linear double layer model, and also using the impedance of the double layer obtained from experimental data. The ac electro-osmotic flow at the surface of the electrodes is then calculated using the Helmholtz-Smoluchowski formula. The bulk fluid flow driven by this surface velocity is numerically calculated as a function of frequency and good agreement is found between the numerical and experimental streamlines.

404 citations


Journal ArticleDOI
TL;DR: In this paper, the efficacy of large-eddy simulation (LES) with wall modeling for complex turbulent flows is assessed by considering turbulent boundary-layer flows past an asymmetric trailing edge.
Abstract: The efficacy of large-eddy simulation (LES) with wall modeling for complex turbulent flows is assessed by considering turbulent boundary-layer flows past an asymmetric trailing-edge. Wall models based on turbulent boundary-layer equations and their simpler variants are employed to compute the instantaneous wall shear stress, which is used as approximate boundary conditions for the LES. It is demonstrated that, as first noted by Cabot and Moin [Flow Turb. Combust. 63, 269 (2000)], when a Reynolds-averaged Navier–Stokes type eddy viscosity is used in the wall-layer equations with nonlinear convective terms, its value must be reduced to account for only the unresolved part of the Reynolds stress. A dynamically adjusted mixing-length eddy viscosity is used in the turbulent boundary-layer equation model, which is shown to be considerably more accurate than the simpler wall models based on the instantaneous log law. This method predicts low-order velocity statistics in good agreement with those from the full LES with resolved wall-layers, at a small fraction of the original computational cost. In particular, the unsteady separation near the trailing-edge is captured correctly, and the prediction of surface pressure fluctuations also shows promise.

Journal ArticleDOI
TL;DR: In this article, an analysis of the propagation of a penny-shaped hydraulic fracture in an impermeable elastic rock is presented, where the fracture is driven by an incompressible Newtonian fluid injected from a source at the center of the fracture.

Journal ArticleDOI
TL;DR: A dedicated minimization-based motion estimator based on an integrated version of the continuity equation of fluid mechanics, which is compatible with large displacements and associated with an original second-order div-curl regularization.
Abstract: In this paper, we address the problem of estimating and analyzing the motion of fluids in image sequences. Due to the great deal of spatial and temporal distortions that intensity patterns exhibit in images of fluids, the standard techniques from computer vision, originally designed for quasi-rigid motions with stable salient features, are not well adapted in this context. We thus investigate a dedicated minimization-based motion estimator. The cost function to be minimized includes a novel data term relying on an integrated version of the continuity equation of fluid mechanics, which is compatible with large displacements. This term is associated with an original second-order div-curl regularization which prevents the washing out of the salient vorticity and divergence structures. The performance of the resulting fluid flow estimator is demonstrated on meteorological satellite images. In addition, we show how the sequences of dense motion fields we estimate can be reliably used to reconstruct trajectories and to extract the regions of high vorticity and divergence.

Journal ArticleDOI
TL;DR: In this paper, a three-dimensional model was developed to simulate the fluid dynamics, heat transfer and phase change that occur when a molten metal droplet falls onto a flat substrate.

Patent
07 Oct 2002
TL;DR: A non-linear flow restrictor that limits the maximum flow rate in a medical aspiration system (10) was proposed in this article to generate nonlinear effects in the fluid, which may define a pressure versus flowrate curve that has a flat portion where the flowrate does not increase with an increase in pressure.
Abstract: A non-linear flow restrictor (50) that limits the maximum flowrate in a medical aspiration system (10). The flow restrictor (50) changes the direction of fluid flow to generate non-linear effects in the fluid. This creates a non-linear relationship between the pressure within the system and the flowrate of the fluid. The non-linear relationship may define a pressure versus flowrate curve that has a flat portion where the flowrate does not increase with an increase in pressure.

Journal ArticleDOI
TL;DR: In this paper, the concept of enhancing parabolic convective heat transfer by reducing the intersection angle between velocity and temperature gradient is reviewed and extended to elliptic fluid flow and heat transfer situation.

Journal ArticleDOI
TL;DR: In this paper, a theoretical model for the prediction of pressure drop in a Newtonian fluid flowing through highly porous, isotropic metallic foams is presented, based on a rigorous assumption of piece-wise plane Poiseuille flow and a simplistic geometrical model, and shows promise to accurately predict the hydrodynamic conditions in both the Darcy and Forchheimer regimes.

Journal ArticleDOI
TL;DR: In this article, the specific features of fluid flow through multiplate micro-channel reactors are examined by an approximate pressure drop model whose validity is confirmed through comparison with more detailed finite-volume calculations.
Abstract: Velocity and residence time distributions play a crucial role in the performance of microreactors for chemical synthesis. The specific features of fluid flow through multiplate microchannel reactors are examined by an approximate pressure drop model whose validity is confirmed through comparison with more detailed finite-volume calculations. The model results allow for determination of the influence of the geometrical characteristics of the microchannel structures on the flow distributions and are used to optimize the reactor design for maximum flow uniformity.

Journal ArticleDOI
TL;DR: In this paper, the steady-state Poiseuille flow of a simple fluid in carbon nanopores under a gravitylike force is simulated using a realistic empirical many-body potential model for carbon.
Abstract: Steady-state Poiseuille flow of a simple fluid in carbon nanopores under a gravitylike force is simulated using a realistic empirical many-body potential model for carbon. Building on our previous study of slit carbon nanopores we show that fluid flow in a nanotube is also characterized by a large slip length. By analyzing temporal profiles of the velocity components of particles colliding with the wall we obtain values of the Maxwell coefficient defining the fraction of molecules thermalized by the wall and, for the first time, propose slip boundary conditions for smooth continuum surfaces such that they are equivalent in adsorption, diffusion, and fluid flow properties to fully dynamic atomistic models.

Journal ArticleDOI
TL;DR: In this paper, a multi-block LBE method for viscous flow computations is proposed. But it requires high resolution near the body and/or there is a far-field boundary.
Abstract: Compared to the Navier–Stokes equation-based approach, the method of lattice Boltzmann Equation (LBE) offers an alternative treatment for fluid dynamics. The LBE method often employs uniform lattices to maintain a compact and efficient computational procedure, which makes it less efficient to perform flow simulations when there is a need for high resolution near the body and/or there is a far-field boundary. To resolve these difficulties, a multi-block method is developed. An accurate, conservative interface treatment between neighboring blocks is adopted, and demonstrated that it satisfies the continuity of mass, momentum, and stresses across the interface. Several test cases are employed to assess accuracy improvement with respect to grid refinement, the impact of the corner singularity, and the Reynolds number scaling. The present multi-block method can substantially improve the accuracy and computational efficiency of the LBE method for viscous flow computations. Copyright © 2002 John Wiley & Sons, Ltd.

Journal ArticleDOI
TL;DR: In this article, a three-dimensional laser-keyhole welding model is developed, featuring the self-consistent evolution of the liquid/vapor (L/V) interface together with full simulation of fluid flow and heat transfer.
Abstract: A three-dimensional laser-keyhole welding model is developed, featuring the self-consistent evolution of the liquid/vapor (L/V) interface together with full simulation of fluid flow and heat transfer. Important interfacial phenomena, such as free surface evolution, evaporation, kinetic Knudsen layer, homogeneous boiling, and multiple reflections, are considered and applied to the model. The level set approach is adopted to incorporate the L/V interface boundary conditions in the Navier-Stokes equation and energy equation. Both thermocapillary force and recoil pressure, which are the major driving forces for the melt flow, are incorporated in the formulation. For melting and solidification processes at the solid/liquid (S/L) interface, the mixture continuum model has been employed. The article consists of two parts. This article (Part I) presents the model formulation and discusses the effects of evaporation, free surface evolution, and multiple reflections on a steady molten pool to demonstrate the relevance of these interfacial phenomena. The results of the full keyhole simulation and the experimental verification will be provided in the companion article (Part II).

Journal ArticleDOI
TL;DR: In this article, the authors show that the threshold propagation distance at which stress drop starts to dominate over frictionally induced stress drop is proportional to the square root of hydraulic diffusivity times the elapsed time.
Abstract: [1] The heat generated in a slip zone during an earthquake can raise fluid pressure and thereby reduce frictional resistance to slip. The amount of fluid pressure rise depends on the associated fluid flow. The heat generated at a given time produces fluid pressure that decreases inversely with the square root of hydraulic diffusivity times the elapsed time. If the slip velocity function is crack-like, there is a prompt fluid pressure rise at the onset of slip, followed by a slower increase. The stress drop associated with the prompt fluid pressure rise increases with rupture propagation distance. The threshold propagation distance at which thermally induced stress drop starts to dominate over frictionally induced stress drop is proportional to hydraulic diffusivity. If hydraulic diffusivity is 0.02 m2/s, estimated from borehole samples of fault zone material, the threshold propagation distance is 300 m. The stress wave in an earthquake will induce an unknown amount of dilatancy and will increase hydraulic diffusivity, both of which will lessen the fluid pressure effect. Nevertheless, if hydraulic diffusivity is no more than two orders of magnitude larger than the laboratory value, then stress drop is complete in large earthquakes.

Journal ArticleDOI
TL;DR: In this article, a 3D spatially unsplit implementation of the piecewise parabolic (PPM) method is presented for the explicit Eulerian finite difference computation of shock capturing problems involving multiple resolved material phases in three dimensions.

Journal ArticleDOI
TL;DR: In this paper, the authors performed a computational study of spatially evolving three-dimensional planar turbulent jets utilizing direct numerical simulation and found that the large scale in the flow field adjust slowly to variations in the local mean velocity gradients, the small scales adjust rapidly.
Abstract: Turbulent plane jets are prototypical free shear flows of practical interest in propulsion, combustion and environmental flows. While considerable experimental research has been performed on planar jets, very few computational studies exist. To the authors' knowledge, this is the first computational study of spatially evolving three-dimensional planar turbulent jets utilizing direct numerical simulation. Jet growth rates as well as the mean velocity, mean scalar and Reynolds stress profiles compare well with experimental data. Coherency spectra, vorticity visualization and autospectra are obtained to identify inferred structures. The development of the initial shear layer instability, as well as the evolution into the jet column mode downstream is captured well.The large- and small-scale anisotropies in the jet are discussed in detail. It is shown that, while the large scales in the flow field adjust slowly to variations in the local mean velocity gradients, the small scales adjust rapidly. Near the centreline of the jet, the small scales of turbulence are more isotropic. The mixing process is studied through analysis of the probability density functions of a passive scalar. Immediately after the rollup of vortical structures in the shear layers, the mixing process is dominated by large-scale engulfing of fluid. However, small-scale mixing dominates further downstream in the turbulent core of the self-similar region of the jet and a change from non-marching to marching PDFs is observed. Near the jet edges, the effects of large-scale engulfing of coflow fluid continue to influence the PDFs and non-marching type behaviour is observed.

Journal ArticleDOI
TL;DR: In this article, a hydraulically driven fracture propagating in an impermeable, linear elastic medium is analyzed, where the fracture is driven by injection of an incompressible, viscous fluid with power-law rheology and behaviour index n⩾ 0.
Abstract: This paper analyses the problem of a hydraulically driven fracture, propagating in an impermeable, linear elastic medium. The fracture is driven by injection of an incompressible, viscous fluid with power-law rheology and behaviour index n⩾0. The opening of the fracture and the internal fluid pressure are related through the elastic singular integral equation, and the flow of fluid inside the crack is modelled using the lubrication theory. Under the additional assumptions of negligible toughness and no lag between the fluid front and the crack tip, the problem is reduced to self-similar form. A solution that describes the crack length evolution, the fracture opening, the net fluid pressure and the fluid flow rate inside the crack is presented. This self-similar solution is obtained by expanding the fracture opening in a series of Gegenbauer polynomials, with the series coefficients calculated using a numerical minimization procedure. The influence of the fluid index n in the crack propagation is also analysed. Copyright © 2002 John Wiley & Sons, Ltd.

Book
01 Jan 2002
TL;DR: The Navier-Stokes System in Domians with Cylindrical Outlets to infinity (Konstantin Pileckas) and periodic homogenization problems in Incompressible Fluid Equations (Carlos Conca and M.R. Vanninathan).
Abstract: Preface On the Contact Topology and Geometry of Ideal Fluids (Robert Christ) Shock Reflection in Gas Dynamics (Denis Serre) The Mathematical Theory of the Incompressible Limit in Fluid Dynamics (Steven Schochet) Local Regularity Theory of Navier-Stokes Equations (Gregory Seregin) On the Influence of the Earth's Rotation on Geophysical Flows (Isabelle Gallagher and Laure Saint-Raymond) The Foundations of Oceanic Dynamics and Climate Modelling (George R. Sell) Mathematical Properties of the Solutions to the Equations Governing the Flow of Fluids with Pressure and Shear Rate Dependent Viscosities (Josef Malek and K.R. Rajagopal) Navier-Stokes System in Domians with Cylindrical Outlets to Infinity (Konstantin Pileckas) Periodic Homogenization Problems in Incompressible Fluid Equations (Carlos Conca and M. Vanninathan) Author Index Subject Index

Journal ArticleDOI
TL;DR: The observed flow rates for small h are larger than theoretical expectations, implying significant slip at the walls, and values of the slip length are estimated.
Abstract: We describe studies of the pressure driven flow of several classical fluids through lithographically produced channels in which one dimension, the channel height h, is in the micron or nanometer size range. The measured flow rates are compared with theoretical predictions assuming no-slip boundary conditions at the walls of the channel. The results for water agree well with this prediction for h as small as 40 nm (our smallest channels). However, for hexane, decane, hexadecane, and silicone oil we find deviations from this theory when h is reduced below about 100 nm. The observed flow rates for small h are larger than theoretical expectations, implying significant slip at the walls, and values of the slip length are estimated. The results are compared with previous experimental and theoretical work.

Patent
28 Aug 2002
TL;DR: In this paper, the authors present a method and apparatus for controlling fluid flow with pressure gradient fluid control, where passive fluid flow barriers are used to act as valves, thereby allowing the flow of fluids through flow paths to be regulated so as to allow fluids to be introduced via a single channel and subsequently split into multiple channels.
Abstract: Methods and apparatus are presented for controlling fluid flow with pressure gradient fluid control. Passive fluid flow barriers may be used to act as valves, thereby allowing the flow of fluids through flow paths to be regulated so as to allow fluids to be introduced via a single channel (50) and subsequently split into multiple channels (58, 60). Flow through flow paths can be regulated to allow a series of sister wells (51-53) or chambers to all fill prior to the fluid flowing beyond any one of the sister wells (51-53) or chambers. Each flow path may have multiple segments (66-69), at least one of which is designed to balance the pressure drops of the flow paths to provide uniform flow of fluids through the flow paths. The configurations of the wells (51-53) may be modified by adding vents or flow dividers to enhance fluid flushing and gas removal capability.


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the fluid dynamics of high-speed (500 m/s) small size (200 μm in diameter) droplet impact on a rigid substrate.
Abstract: We are investigating the fluid dynamics of high-speed (500 m/s) small size (200 μm in diameter) droplet impact on a rigid substrate. Utilizing a high-resolution axisymmetric solver for the Euler equations, we show that the compressibility of the liquid medium plays a dominant role in the evolution of the phenomenon. Compression of the liquid in a zone defined by a shock wave envelope, very high velocity lateral jetting, and expansion waves in the bulk of the medium are the most important mechanisms identified, simulated, and discussed. Comparisons of computationally obtained jetting inception times with analytic results show that agreement improves significantly if the radial motion of liquid in the compressed area is taken into account.