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Plug Flow (plug + flow)

Distribution by Scientific Domains
Chemistry66%

Terms modified by Plug Flow

  • plug flow reactor
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    Selected Abstracts

    Optimization of Operating Temperature for Continuous Immobilized Glucose Isomerase Reactor with Pseudo Linear Kinetics

    ENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 5 2004
    N.M. Faqir
    Abstract In this work, the optimal operating temperature for the enzymatic isomerization of glucose to fructose using a continuous immobilized glucose isomerase packed bed reactor is studied. This optimization problem describing the performance of such reactor is based on reversible pseudo linear kinetics and is expressed in terms of a recycle ratio. The thermal deactivation of the enzyme as well as the substrate protection during the reactor operation is considered. The formulation of the problem is expressed in terms of maximization of the productivity of fructose. This constrained nonlinear optimization problem is solved using the disjoint policy of the calculus of variations. Accordingly, this method of solution transforms the nonlinear optimization problem into a system of two coupled nonlinear ordinary differential equations (ODEs) of the initial value type, one equation for the operating temperature profile and the other one for the enzyme activity. The ODE for the operating temperature profile is dependent on the recycle ratio, operating time period, and the reactor residence time as well as the kinetics of the reaction and enzyme deactivation. The optimal initial operating temperature is selected by solving the ODEs system by maximizing the fructose productivity. This results into an unconstrained one-dimensional optimization problem with simple bounds on the operating temperature. Depending on the limits of the recycle ratio, which represents either a plug flow or a mixed flow reactor, it is found that the optimal temperature of operation is characterized by an increasing temperature profile. For higher residence time and low operating periods the residual enzyme activity in the mixed flow reactor is higher than that for the plug flow reactor, which in turn allows the mixed flow reactor to operate at lower temperature than that of the plug flow reactor. At long operating times and short residence time, the operating temperature profiles are almost the same for both reactors. This could be attributed to the effect of substrate protection on the enzyme stability, which is almost the same for both reactors. Improvement in the fructose productivity for both types of reactors is achieved when compared to the constant optimum temperature of operation. The improvement in the fructose productivity for the plug flow reactor is significant in comparison with the mixed flow reactor. [source]

    Shape of isolated bubble in intermittent flows in a horizontal pipe

    HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 5 2007
    Gu Hanyang
    Abstract An experimental study on the shape of a single bubble similar to those observed in a horizontal plug/slug flow was performed using visual observation and conductance probes. The results indicated that the shapes of the bubble nose and the bubble body depend on the Froude number defined by gas/liquid mixture velocity, whereas the shape of the back region of the bubble depends on both the Froude number and bubble length. The photographic images showed that the structural feature of the bubble head is related to the motion characteristics of the bubble. The transition from plug flow to slug flow occurs when the tail of the bubble changes from a staircase to hydraulic jump pattern with the increasing of the Froude number and bubble length. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(5): 276, 285, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20161 [source]

    Using Rheology to Achieve Co-Extrusion of Cement-Based Materials with Graded Cellular Structures

    INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2008
    Yunbo Chen
    Co-extrusion involves simultaneous extrusion of multiple layers and can be used to produce functionally graded materials whose layers have different properties. Rheological control is vital for successful co-extrusion. During extrusion, flow in the barrel and die land in a ram extruder should be plug-like, while the paste should be sheared and uniformly elongated in the die entry region. In the barrel of the extruder, the paste flow velocity field was inferred by direct observation of the paste left in the barrel, and evidence for plug flow in the barrel was seen only at low-extrudate velocities. In the die land, the Benbow nonlinear model was employed to assess the paste flow behavior, and plug flow was achieved only when the shear stress applied to the paste by the die land wall was smaller than its yield stress. For co-extrusion, a simple method using thin-walled tubes was found to be effective to prepare layered feedrods. Functionally graded cellular structures of cement-based materials were successfully co-extruded by using a low-extrudate velocity when the paste had decreasing shear viscosity from inner to outer layers. [source]

    Mass transport and flow regimes in centrifugal partition chromatography

    AICHE JOURNAL, Issue 8 2002
    L. Marchal
    Centrifugal partition chromatography (CPC) is a support-free liquid,liquid separation process that depends for efficiency on the behavior of the two liquid phases. Hydrodynamics of phases was studied according to flow rate and centrifugal acceleration, using a transparent column and a stroboscopic video system. For the heptane-methanol two-phase system, three main flow regimes,stuck film, oscillating sheet, and atomization,are observed, highlighting the coriolis acceleration effect as well as the influence of the column shape. Mass transport in the CPC column is modeled by a plug flow with axial dispersion and mass transfer with a stagnant volume. Model parameters (residence time, Péclet number, partition ratio, and mass-transfer coefficient) are fitted on solute residence-time distribution. Off-column dispersion is an important source of peak broadening in CPC, whereas its irregular geometry provides a plug flow for mobile phase. Importance of flow pattern on mass transfer is demonstrated. CPC interest for preparative applications is confirmed. [source]

    Near Wall Studies of Pulp Suspension Flow Using LDA

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2006
    A. Johan Pettersson
    Abstract A detailed study of the flow behaviour in the near wall region of pulp suspensions up to 4.7% have been performed using Laser Doppler Anemometry (LDA) in pipe flow. Axial mean velocity profiles show a distinct plug flow and an increase of the plug region as the flow rate decreases and fibre concentration increases. An attempt is made to relate the LDA data-rate to fibre concentration, which indicates a dilution region at 1-2 mm from the wall that is larger than the annulus region. The dilution region increases with increasing flow rate, decreasing concentration and when using longer pulp fibres. On a réalisé une étude détaillée du comportement d'un écoulement dans la région proche de la paroi de suspensions de pâte jusqu'à 4,7 %, en utilisant l'anémométrie laser Doppler (LDA) dans une conduite. Les profils de vitesse axiale moyens montrent un écoulement piston distinct et une augmentation de la région piston lorsque le débit diminue et la concentration de fibres augmente. Une tentative est faite pour relier les données de vitesse LDA à la concentration de fibres, qui indique une région de dilution à 1-2 mm de la paroi plus grande que l'espace annulaire. La région de dilution augmente avec l'augmentation du débit, la diminution de la concentration et l'utilisation de fibres de pâtes plus longues. [source]

    Selectivity, Hydrodynamics and Solvent Effects in a Monolith Cocurrent Downflow Contactor (CDC) Reactor

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
    Mike Winterbottoma
    Abstract The liquid phase hydrogenation of 2-butyne-1,4-diol (B) to cis-2-butene-1,4,-diol (C) was studied in a Monolith (CDC) Reactor. The effect of temperature, pressure, different solvents and gas and liquid feed rates on reaction rate and selectivity was determined. RTD measurements were made under different hydrodynamic conditions. The liquid flow was largely laminar with evidence of a stagnant wall film. Selectivity to C was observed to increase with hydrogen pressure and approaches 1 at high superficial gas velocities and conversion of B (>95%) as plug flow is approached. The flow regime was of influence on selectivity and kinetics, which was described by a dual site Langmuir-Hinshelwood mechanism. L'hydrogénation en phase liquide du butyne-2-diol-1,4 B en cis-butène-2-diol-1,4 C a été étudiée dans un réacteur à monolithe (CDC). On a déterminé l'effet de la température, de la pression, des différents solvants et des vitesses d'alimentation de gaz et de liquide sur la vitesse de réaction et la sélectivité. Des mesures de distribution de temps de séjour ont été effectuées pour différentes conditions hydrodynamiques. L'écoulement du liquide est largement laminaire avec un film de paroi stagnant évident. On a observé que la sélectivité pour C augmentait avec la pression de l'hydrogène et s'approchait de 1 à des vitesses de gaz superficielles élevées et à conversion de B élevée (>95%) quand l'écoulement piston devient piston. Le régime d'écoulement a une influence sur la sélectivité et la cinétique, et celle-ci est bien décrite par un mécanisme à site double de Langmuir-Hinshelwood. [source]

    Pressure Drop in Liquid-liquid Two Phase Horizontal Flow: Experiment and Prediction

    CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2005
    D. P. Chakrabarti
    Abstract The present study is aimed at an investigation of the pressure drop characteristics during the simultaneous flow of a kerosene-water mixture through a horizontal pipe of 0.025,m diameter. Measurements of pressure gradient were made for different combinations of phase superficial velocities ranging from 0.03,2,m/s such that the regimes encountered were smooth stratified, wavy stratified, three layer flow, plug flow and oil dispersed in water, and water flow patterns. A model was developed, which considered the energy minimization and pressure equalization of both phases. [source]

    CFD Modeling of a Bubble Column Reactor Carrying out a Consecutive A , B , C Reaction

    CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 4 2004
    J.M. van Baten
    Abstract In this paper, we develop a CFD model for describing a bubble column reactor for carrying out a consecutive first-order reaction sequence A , B , C. Three reactor configurations, all operating in the homogeneous bubbly regime, were investigated: (I) column diameter DT = 0.1 m, column height HT = 1.1 m, (II) DT = 0.1 m, HT = 2 m, and (III) DT = 1 m, HT = 5 m. Eulerian simulations were carried out for superficial gas velocities UG in the range of 0.005,0.04 m/s, assuming cylindrical axisymmetry. Additionally, for configurations I and III fully three-dimensional transient simulations were carried out for checking the assumption of cylindrical axisymmetry. For the 0.1 m diameter column (configuration I), 2-D axisymmetric and 3-D transient simulations yield nearly the same results for gas holdup ,G, centerline liquid velocity VL(0), conversion of A, ,A, and selectivity to B, SB. In sharp contrast, for the 1 m diameter column (configuration III), there are significant differences in the CFD predictions of ,G, VL(0), ,A, and SB using 2-D and 3-D simulations; the 2-D strategies tend to exaggerate VL(0), and underpredict ,G, ,A, and SB. The transient 3-D simulation results appear to be more realistic. The CFD simulation results for ,A and SB are also compared with a simple analytic model, often employed in practice, in which the gas phase is assumed to be in plug flow and the liquid phase is well mixed. For the smaller diameter columns (configurations I and II) the CFD simulation results for ,A are in excellent agreement with the analytic model, but for the larger diameter column the analytic model is somewhat optimistic. There are two reasons for this deviation. Firstly, the gas phase is not in perfect plug flow and secondly, the liquid phase is not perfectly mixed. The computational results obtained in this paper demonstrate the power of CFD for predicting the performance of bubble column reactors. Of particular use is the ability of CFD to describe scale effects. [source]