Laminar Flow Profile Research Articles

PSE를 이용한 익형 위 경계층 안정성 해석

경계층 안정성 방정식인 PSE를 이용하여 익형 표면에 형성되는 경계층의 안정성 해석을 수행하였다. 압축성 비점성 유동 해석으로 경계층 가장자리 조건을 얻고, 일반좌표계에서의 압축성 경계층 방정식을 4차 정확도로 계산하여 층류 경계층 유동장을 얻었다. 층류 경계층 데이터를 PSE의 입력으로 하여 안정성 해석을 수행하고 교란의 증폭률을 얻어 안정성 특성을 고찰 하였다. 마하수 0.5의 NACA0012 및 HSNLF(1)-0213 익형에 대한 해석을 수행하여 교란 주파수에 따른 증폭률 및 위치에 따른 교란의 진폭 분포 특성을 파악하였다. 익형의 윗면과 아랫면에서 받음각에 따른 안정성 특성을 각각 증폭률의 크기와 주파수 범위에 대해 분석하였다. 또한 중립안정성 곡선, 마하수에 따른 안정성 특성을 살펴보았으며 익형의 종류에 따른 안정성 특성 차이를 분석하였다. In this study, stability analysis of boundary layers on airfoils is performed by using parabolized stability equations(PSE). Boundary layer edge conditions are obtained by compressible inviscid flow calculations. Mean velocity and temperature profiles of the laminar boundary layer are obtained by solving compressible boundary layer equations in generalized curvilinear coordinates with fourth order accuracy in the wall normal direction. Laminar mean flow profiles are used as input data for PSE to investigate growth rates of disturbances and stability characteristics. For the cases of boundary layer on NACA0012 and HSNLF(1)-0213 airfoils at Mach number 0.5, growth rates with respect to disturbance frequencies and profiles of disturbance amplitude are investigated. The effect of angle of attack on stability characteristics are examined at both upper and lower surfaces. The neutral stability curves, effect of Mach number and effect of airfoil section shapes are also analyzed.

Transverse diffusion of laminar flow profiles – a generic method for mixing reactants in capillary microreactor

The capillary is an attractive format for integrated microanalyses, which start with the injection of separate reactants into the capillary and their mixing inside the capillary. Due to the nonturbulent nature of flow inside the capillary, mixing reactants in a generic way is a challenging task. Three approaches have been suggested as a solution: mixing by electrophoresis, mixing by longitudinal diffusion, and, most recently, mixing by transverse diffusion of laminar flow profiles (TDLFP). This is the first review on TDLFP, describing: (i) the physical basis of the method, (ii) its theory, (iii) analytical and numerical solutions for the calculation of concentration profiles of mixed reactants, (iv) up-to-date applications, and (v) problems to be solved and future directions.

Linear blood pump: First results of a lab version with carbonic surface

In order to combine membrane and rotating related principle we propose a new concept for a blood pump that is not in need of membranes or rotating properties, but mimic the displacement of an inlet valve against an outlet valve as it is also part of the natural cardiac cycle (see Figure). A linear induction motor creates a gradient depending displacement which refers to some extent to the velocity field of rotational pumps. In addition, the new concept allows refinement of all blood- contact surfaces with carbon or ceramics combined with a nearly laminar flow profile. After development of different steering modes, we built a lab-version with a nearly fully carbonised blood contact surface (see figure). In mock-circulation we tested hemodynamic and electrical parameters like pump volume, pressure curves, efficacy and regulation properties. Depending on pre- and afterload and energy consumption of between 2 to 40 Watts pumping volume ranged from 1 to 15l/min at 80 to 250mmHg systolic pressure and a frequency of 10 to 200 beats per minute. These pre-liminary data make a small, effective and powerfull system for construction of blood pump devices feasible.

Kinetic capillary electrophoresis-based affinity screening of aptamer clones

DNA aptamers are single stranded DNA (ssDNA) molecules artificially selected from random-sequence DNA libraries for their specific binding to a certain target. DNA aptamers have a number of advantages over antibodies and promise to replace them in both diagnostic and therapeutic applications. The development of DNA aptamers involves three major stages: library enrichment, obtaining individual DNA clones, and the affinity screening of the clones. The purpose of the screening is to obtain the nucleotide sequences of aptamers and the binding parameters of their interaction with the target. Highly efficient approaches have been recently developed for the first two stages, while the third stage remained the rate-limiting one. Here, we introduce a new method for affinity screening of individual DNA aptamer clones. The proposed method amalgamates: (i) aptamer amplification by asymmetric PCR (PCR with a primer ratio different from unity), (ii) analysis of aptamer–target interaction, combining in-capillary mixing of reactants by transverse diffusion of laminar flow profiles (TDLFP) and affinity analysis using kinetic capillary electrophoresis (KCE), and (iii) sequencing of only aptamers with satisfying binding parameters. For the first time we showed that aptamer clones can be directly used in TDLFP/KCE-based affinity analysis without an additional purification step after asymmetric PCR amplification. We also demonstrated that mathematical modeling of TDLFP-based mixing allows for the determination of K d values for the in-capillary reaction of an aptamer and a target and that the obtained K d values can be used for the accurate affinity ranking of aptamers. The proposed method does not require the knowledge of aptamer sequences before screening, avoids lengthy (3–5 h) purification steps of aptamer clones, and minimizes reagent consumption to nanoliters.

Mathematical Model for Mixing Reactants in a Capillary Microreactor by Transverse Diffusion of Laminar Flow Profiles

Transverse diffusion of laminar flow profiles (TDLFP) was recently suggested as a generic approach for mixing reactants inside a capillary microreactor. Conceptually, solutions of reactants are injected inside the capillary by high pressure as a series of consecutive plugs. Because of the laminar nature of the flow inside the capillary, the nondiffused plugs have parabolic profiles with predominantly longitudinal interfaces between the plugs. After the injection, the reactants are mixed by transverse diffusion across the longitudinal interfaces. TDLFP-based mixing is still in its infancy as only the principle was proved. Here, we develop the theory of TDLFP and introduce a dimensionless parameter, York number, which can be used in predicting the quality of TDLFP-based mixing. The theory uses a single simplifying assumption that the longitudinal diffusion is negligible; this assumption is readily satisfied. We then develop a numerical model of TDLFP and use it to simulate the concentration profiles of three reactants mixed by TDLFP in the capillary. The correlation between the York number and quality of mixing is analyzed. Two ways of improving the quality of TDLFP-based mixing are suggested and studied: (i) increasing the longitudinal interface between the plugs by a long last plug of a solvent and (ii) "shaking" the injected reactants by a series of alternating negative and positive pressure pulses. The developed theory and computational simulation of TDLFP will stimulate the practical use of capillary microreactors.

“Inject-Mix-React-Separate-and-Quantitate” (IMReSQ) Method for Screening Enzyme Inhibitors

Many regulatory enzymes are considered attractive therapeutic targets, and their inhibitors are potential drug candidates. Screening combinatorial libraries for enzyme inhibitors is pivotal to identifying hit compounds for the development of drugs targeting regulatory enzymes. Here, we introduce the first inhibitor screening method that consumes only nanoliters of the reactant solutions and is applicable to regulatory enzymes. The method is termed inject-mix-react-separate-and-quantitate (IMReSQ) and includes five steps. First, nanoliter volumes of substrate, candidate inhibitor, and enzyme solutions are injected by pressure into a capillary as separate plugs. Second, the plugs are mixed inside this capillary microreactor by transverse diffusion of laminar flow profiles. Third, the reaction mixture is incubated to form the enzymatic product. Fourth, the product is separated from the substrate inside the capillary by electrophoresis. Fifth, the amounts of the product and substrate are quantitated. In this proof-of-principle work, we applied IMReSQ to study inhibition of recently cloned protein farnesyltransferase from parasite Entamoeba histolytica. This enzyme is a potential therapeutic target for antiparasitic drugs. We identified three previously unknown inhibitors of this enzyme and proved that IMReSQ could be used for quantitatively ranking the potencies of inhibitors.

HIGH-TEMPERATURE SOLAR CHEMICAL REACTORS FOR HYDROGEN PRODUCTION FROM NATURAL GAS CRACKING

This study deals with the thermal cracking of natural gas for the coproduction of hydrogen and carbon black from concentrated solar energy without CO2 emission. A laboratory-scale solar reactor (1 kW) was tested and modeled successfully. It consists of a tubular graphite receiver directly absorbing solar radiation, in which a mixture of Ar and CH4 flows. A temperature increase or a gas flow rate decrease results in chemical conversion increase. Methane conversion higher than 75% was obtained. Reaction occurred near the wall where temperature is maximal and gas velocity is minimal due to the laminar flow profile. The work focused also on the design of a medium-scale tubular solar reactor (10 kW) based on the indirect heating concept. A reactor model including gas hydrodynamics and heat and mass transfers coupled to the chemical reaction was developed in order to predict the reactor performances. Temperature and species concentration profiles and final chemical conversion were quantified. According to the results, temperature was uniform in the tubular reaction zone and the predicted chemical conversion was 65%, neglecting the catalytic effect of carbon particles.

Comment on “Pinched Flow Fractionation: Continuous Size Separation of Particles Utilizing a Laminar Flow Profile in a Pinched Microchannel”

[First paragraph] In a recent paper Yamada et al. propose the novel concept of "pinched flow fractionation" (PFF) for the continuous size separation and analysis of particles in microfabricated lab-on-a-chip devices. In their description of the basic principle they claim that especially the width of the pinched and broadened segments will affect theseparation performance. In the following we comment on the physics behind this statement.

Steady states and linear stability analysis of precipitation pattern formation at geothermal hot springs

A dynamical theory of geophysical precipitation pattern formation is presented and applied to irreversible calcium carbonate (travertine) deposition. Specific systems studied here are the terraces and domes observed at geothermal hot springs, such as those at Yellowstone National Park, and speleothems, particularly stalactites and stalagmites. The theory couples the precipitation front dynamics with shallow water flow, including corrections for turbulent drag and curvature effects. In the absence of capillarity and with a laminar flow profile, the theory predicts a one-parameter family of steady state solutions to the moving boundary problem describing the precipitation front. These shapes match the measured shapes near the vent at the top of observed travertine domes well. Closer to the base of the dome, the solutions deviate from observations and circular symmetry is broken by a fluting pattern, which we show is associated with capillary forces causing thin film break-up. We relate our model to that recently proposed for stalactite growth, and calculate the linear stability spectrum of both travertine domes and stalactites. Lastly, we apply the theory to the problem of precipitation pattern formation arising from turbulent flow down an inclined plane and identify a linear instability that underlies scale-invariant travertine terrace formation at geothermal hot springs.

Free Flow Acoustophoresis: Microfluidic-Based Mode of Particle and Cell Separation

A novel method, free flow acoustophoresis (FFA), capable of continuous separation of mixed particle suspensions into multiple outlet fractions is presented. Acoustic forces are utilized to separate particles based on their size and density. The method is shown to be suitable for both biological and nonbiological suspended particles. The microfluidic separation chips were fabricated using conventional microfabrication methods. Particle separation was accomplished by combining laminar flow with the axial acoustic primary radiation force in an ultrasonic standing wave field. Dissimilar suspended particles flowing through the 350-microm-wide channel were thereby laterally translated to different regions of the laminar flow profile, which was split into multiple outlets for continuous fraction collection. Using four outlets, a mixture of 2-, 5-, 8-, and 10-microm polystyrene particles was separated with between 62 and 94% of each particle size ending up in separate fractions. Using three outlets and three particle sizes (3, 7, and 10 microm) the corresponding results ranged between 76 and 96%. It was also proven possible to separate normally acoustically inseparable particle types by manipulating the density of the suspending medium with cesium chloride. The medium manipulation, in combination with FFA, was further used to enable the fractionation of red cells, platelets, and leukocytes. The results show that free flow acoustophoresis can be used to perform complex separation tasks, thereby offering an alternative to expensive and time-consuming methods currently in use.

Microvascular Branching as a Determinant of Blood Flow by Intravital Particle Imaging Velocimetry

The effects of microvascular branching on blood flow were investigated in vivo by microscopic particle imaging velocimetry (micro-PIV). We use micro-PIV to measure blood flow by tracking red blood cells (RBC) as the moving particles. Velocity flow fields, including flow pulsatility, were analyzed for the first four branching orders of capillaries, postcapillary venules and small veins of the microvascular network within the developing avian yolksac at embryonic day 5 (E5). Increasing volumetric flowrates were obtained from parabolic laminar flow profiles as a function of increasing vessel diameter and branching order. Maximum flow velocities increased approximately twenty-fold as the function of increasing vessel diameter and branching order compared to flow velocities of 100 - 150 micron/sec in the capillaries. Results from our study will be useful for the increased understanding of blood flow within anastomotic, heterogeneous microvascular networks.

Continuous flow separations in microfluidic devices

Biochemical sample mixtures are commonly separated in batch processes, such as filtration, centrifugation, chromatography or electrophoresis. In recent years, however, many research groups have demonstrated continuous flow separation methods in microfluidic devices. Such separation methods are characterised by continuous injection, real-time monitoring, as well as continuous collection, which makes them ideal for combination with upstream and downstream applications. Importantly, in continuous flow separation the sample components are deflected from the main direction of flow, either by means of a force field (electric, magnetic, acoustic, optical etc.), or by intelligent positioning of obstacles in combination with laminar flow profiles. Sample components susceptible to deflection can be spatially separated. A large variety of methods has been reported, some of these are miniaturised versions of larger scale methods, others are only possible in microfluidic regimes. Researchers now have a diverse toolbox to choose from and it is likely that continuous flow methods will play an important role in future point-of-care or in-the-field analysis devices.

Cell lysis inside the capillary facilitated by transverse diffusion of laminar flow profiles (TDLFP)

Chemical cytometry studies the molecular composition of individual cells by means of capillary electrophoresis or capillary chromatography. In one of its realizations an intact cell is injected inside the capillary, the plasma membrane is disrupted to release the cellular contents into the separation buffer, and, finally, the molecules of interest are separated and detected. The solubilization of the plasma membrane with a surfactant is a simple and efficient way of achieving cell lysis inside the capillary. To facilitate cell lysis by a surfactant the cell has to be contacted with the surfactant inside the capillary. We recently introduced a generic method for mixing solutions inside the capillary termed transverse diffusion of laminar flow profiles (TDLFP). In this work, we propose that TDLFP can facilitate efficient cell lysis inside the capillary. Conceptually, a short plug of the surfactant is injected by pressure prior to cell injection. The cell is then injected by pressure within a plug of the physiological buffer. Due to the parabolic profiles of pressure-driven laminar flows the interface between the plug of the surfactant and that of the physiological buffer is predominantly longitudinal. Transverse diffusion mixes the surfactant with the physiological buffer, which leads to surfactant's contact with the cell and subsequent cell lysis. Here, we demonstrate that the proposed concept is valid. TDLFP-facilitated cell lysis by a short plug of the surfactant allows us to exclude the surfactant from the run buffer, and, hence, facilitates modes of separation, which are incompatible with the surfactant's presence in the run buffer. In addition to cell lysis, TDLFP will be used to mix the cellular components with labeling reactants, affinity probes, inhibitors, etc. We foresee that the generic nature and enabling capabilities of TDLFP will speed up the maturation of chemical cytometry into a practical bioanalytical tool.

Oscillations in the Gas Channels - The Forgotten Player in Impedance Spectroscopy in Polymer Electrolyte Fuel Cells B. Modeling the Wave

A two-dimensional, steady-state impedance model is presented, rigorously derived from continuum mechanics and conservation laws. The model will reflect unique features of the local impedance response of air-fed PEFCs. Oxygen concentration oscillations originatingfrom the modulated ac current are not confined to the GDL by allowing for a non-zero amplitude at the GDL-channel interface. Therefore, the propagation of oxygen concentration oscillations within the cathodic gas flow becomes possible. To describe the oscillating oxygen concentration field within air-fed PEFC channels during impedance spectroscopy measurements, the fluid dynamics within the channel is approximated by a laminar flow profile. For the sake of simplicity, electrode reactions are assumed to obey Tafel's law. The concentration wave within the channels will be characterized, and the bearings on measurable impedances will be analyzed.

Selective sample recovery of DEP-separated cells and particles by phaseguide-controlled laminar flow

The selective recovery of particles is demonstrated after separation with dielectrophoretic (DEP) forces. Particles are separated based on their size using the so-called cage-speed separation protocol. A two-lane laminar flow enables the selective recovery of the particles. In order to prevent hydrostatic pressure flow, liquid reservoirs are absent. The sample liquid is thus replaced with air during recovery. Phaseguides are introduced in the system to control the liquid–air interface, so that the two-lane laminar flow profile is preserved.

Stabilization of two-phase octanol/water flows inside poly(dimethylsiloxane) microchannels using polymer coatings

In this paper we present our first results on the realization of stable water/octanol, two-phase flows inside poly(dimethylsiloxane) (PDMS) microchannels. Native PDMS microchannels were coated with high molecular weight polymers to change the surface properties of the microchannels and thus stabilize the laminar flow profile. The polymers poly(2-hydroxyethyl methacrylate), poly(vinyl pyrrolidone), poly(ethylene oxide), poly(ethylene glycol), and poly(vinyl alcohol) were assessed for their quality as stabilization coatings after deposition from flowing and stationary solutions. Additionally, the influence of coating the microchannels homogeneously with a single kind of polymer or heterogeneously with two different polymers was investigated. From the experimental observations, it can be concluded that homogeneous polymer coatings with poly(2-hydroxyethyl methacrylate) and poly(vinyl pyrrolidone) led to the effective stabilization of laminar water/octanol flows. Furthermore, heterogeneous coatings led to two-phase flows which had a better-defined and more stable interface over long distances (i.e., 40-mm-long microchannels). Finally, the partitioning of fuchsin dye in the coated microchannels was demonstrated, establishing the feasibility of the use of the polymer-coated PDMS microchannels for determination of logP values in laminar octanol/water flows.

Channel, tube, and Taylor–Couette flow of complex viscoelastic fluid models

We show how to formulate two-point boundary value problems to compute laminar channel, tube, and Taylor–Couette flow profiles for some complex viscoelastic fluid models of differential type. The models examined herein are the Pom-Pom Model [McLeish and Larson 42:81–110, (1998)] the Pompon Model [Ottinger 40:317–321, (2001)] and the Two Coupled Maxwell Modes Model (Beris and Edwards 1994). For the two-mode Upper-Convected Maxwell Model, we calculate analytical solutions for the three flow geometries and use the solutions to validate the numerical methodology. We illustrate how to calculate the velocity, pressure, conformation tensor, backbone orientation tensor, backbone stretch, and extra stress profiles for various models. For the Pom-Pom Model, we find that the two-point boundary value problem is numerically unstable, which is due to the aphysical non-monotonic shear stress vs shear rate prediction of the model. For the other two models, we compute laminar flow profiles over a wide range of pressure drops and inner cylinder velocities. The volumetric flow rate and the nonlinear viscoelastic material properties on the boundaries of the flow geometries are determined as functions of the applied pressure drop, allowing easy analysis of experimentally measurable quantities.

Turbulent flow as a cause for underestimating coronary flow reserve measured by Doppler guide wire

BackgroundDoppler-tipped coronary guide-wires (FW) are well-established tools in interventional cardiology to quantitatively analyze coronary blood flow. Doppler wires are used to measure the coronary flow velocity reserve (CFVR). The CFVR remains reduced in some patients despite anatomically successful coronary angioplasty. It was the aim of our study to test the influence of changes in flow profile on the validity of intra-coronary Doppler flow velocity measurements in vitro. It is still unclear whether turbulent flow in coronary arteries is of importance for physiologic studies in vivo.MethodsWe perfused glass pipes of defined inner diameters (1.5 – 5.5 mm) with heparinized blood in a pulsatile flow model. Laminar and turbulent flow profiles were achieved by varying the flow velocity. The average peak velocity (APV) was recorded using 0.014 inch FW. Flow velocity measurements were also performed in 75 patients during coronary angiography. Coronary hyperemia was induced by intra-coronary injection of adenosine. The APV maximum was taken for further analysis. The mean luminal diameter of the coronary artery at the region of flow velocity measurement was calculated by quantitative angiography in two orthogonal planes.ResultsIn vitro, the measured APV multiplied with the luminal area revealed a significant correlation to the given perfusion volumes in all diameters under laminar flow conditions (r2 > 0.85). Above a critical Reynolds number of 500 – indicating turbulent flow – the volume calculation derived by FW velocity measurement underestimated the actual rate of perfusion by up to 22.5 % (13 ± 4.6 %). In vivo, the hyperemic APV was measured irrespectively of the inherent deviation towards lower velocities. In 15 of 75 patients (20%) the maximum APV exceeded the velocity of the critical Reynolds number determined by the in vitro experiments.ConclusionDoppler guide wires are a valid tool for exact measurement of coronary flow velocity below a critical Reynolds number of 500. Reaching a coronary flow velocity above the velocity of the critical Reynolds number may result in an underestimation of the CFVR caused by turbulent flow. This underestimation of the flow velocity may reach up to 22.5 % compared to the actual volumetric flow. Cardiologists should consider this phenomena in at least 20 % of patients when measuring CFVR for clinical decision making.

Nonequilibrium Capillary Electrophoresis of Equilibrium Mixtures (NECEEM): A Novel Method for Biomolecular Screening

Nonequilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) is a new separation-based affinity method. It has kinetic capabilities exceeding those of surface plasmon resonance (SPR) and does not require immobilization of molecules on the surface. Another distinctive feature of NECEEM is that--if it is combined with an advanced method for the mixing solutions inside a capillary, termed transverse diffusion of laminar flow profiles (TDLFP)--it requires only nanoliter volumes of solutions. The proven applications of NECEEM to biomolecular screening include 1) measuring kinetic and thermodynamic parameters of protein-ligand interactions, 2) quantitative affinity analyses of proteins and hybridization analyses of DNA and RNA, and 3) selection of binding ligands from combinatorial libraries. NECEEM is easy to automate and parallelize. Because of its simplicity and analytical power, NECEEM has the potential to become a workhorse in studies of biomolecular interactions. The author reviews theoretical bases of NECEEM and its applications to biomolecular screening.

Modeling of flow dynamics in laminar aerosol flow tubes

Flow behaviour in laminar aerosol flow tubes was investigated using a Computational Fluid Dynamics (CFD) model. Since these flow tubes are typically operated at low gas velocity, even small temperature gradients produce convection currents strong enough to interfere with laminar flow. This results in recirculation, causing the residence times of aerosol particles to be poorly defined. The situation is exacerbated when temperature inversions are present, or when the flow direction and temperature are changed simultaneously. We analyzed several characteristic flow tube configurations to define the range of experimental conditions that will ensure a laminar flow profile with minimal recirculation. For a laminar flow situation, we evaluated the extent of diffusion-controlled exchange between aerosol and the flow tube wall.