Showing papers on "Laminar flow reactor published in 2007"

Laminar Flame Speeds of Preheated iso-Octane/O2/N2 and n-Heptane/O2/N2 Mixtures

Abstract: Laminar flame speed measurements are carried out for premixed i so-octane/air and n-heptane/air mixtures under conditions of atmospheric pressure, equivalence ratios ranging from 0.7 to 1.4, and unburned mixture temperatures of 298, 360, 400, and 470 K using the counterflow flame technique. These experiments employ the digital particle image velocimetry technique to characterize the two-dimensional flow field upstream of the flame. As such, the reference stretch-affected flame speed and the imposed stretch rate can be simultaneously determined. By systematically varying the imposed stretch rate, the corresponding laminar flame speed is obtained by linearly extrapolating to zero stretch rate. In addition, the effect of nitrogen dilution level on the laminar flame speed is investigated by varying the nitrogen molar percentage in the oxidizer mixture from 78.5 to 80.5%. These results are further used for the determination of overall activation energies at different equivalence ratios. The experimental laminar flame speeds are subsequently compared with the computed values using two iso-octane reaction mechanisms and two n-heptane reaction mechanisms available in the literature, followed by discussion and sensitivity analysis.

A new approach to anodic substitution reaction using parallel laminar flow in a micro-flow reactor.

Abstract: We have developed a novel electrosynthetic system for anodic substitution reaction using a micro-flow reactor. This system enables nucleophilic reactions to overcome the restraints such as the oxidation potential of nucleophiles and the stability of carbocations by the combined use of ionic liquids as reaction media and the parallel laminar flow in the reactor.

Entropy generation analysis of fully developed laminar forced convection in a helical tube with uniform wall temperature

Abstract: In the present study, fully developed laminar flow and heat transfer in a helically coiled tube with uniform wall temperature have been investigated analytically. Expressions involving relevant variables for entropy generation rate contributed to heat transfer and friction loss, and total entropy generation rate have been derived. The effect of various flow and coil parameters like Reynolds number, curvature ratio, coil pitch, etc. on the entropy generation rate has been studied for two fluids- air and water. The results of the present study have been compared to the corresponding entropy generation values of straight pipe. Investigating the results, some optimum values for Reynolds number have been proposed and compared with the optimum Reynolds numbers of laminar flow inside a coiled tube subjected to constant heat flux boundary condition.

Modelling residence time distribution in chemical reactors : A novel generalised n-laminar model Application to supercritical CO2 and subcritical water tubular reactors

Abstract: A new two-parameter RTD model based on the one-parameter laminar flow model has been proposed. The model, ‘n-laminar model’, is defined in time domain and considers a generalization of the parabolic velocity profile across radial direction; its mathematical deduction is presented in text. The model has been validated for both supercritical and near critical CO2 and near critical H2O. It is shown how the proposed two-parameter model works much better than the classical models with one, two or even three parameters for both CO2 and H2O under near critical and supercritical conditions. A range of experiments at 10–30 MPa and 100–250 °C at different flowrates are presented. Traditional models, such as n-tanks in series or a combination of n-tanks with a plug flow resulted in a poor explanation of the behaviour in most cases with average errors over 100%. Laminar flow has shown the best results within all these classical models, with a mean average error of 50%. The proposed model predicts with an average error of less than 10–20%. Thus the generalization of the laminar flow to n-laminar is a significant improvement over traditional models. This model is the first successful attempt for the modelling of RTD curves at high pressures.

Investigation of the starting process in a Ludwieg tube

Abstract: The hypersonic Ludwieg tube Braunschweig (HLB) is a valve-controlled wind tunnel that has been designed for a Mach number of Ma = 5.9 and a Reynolds number range from 2.5 × 106 up to 2.5 × 107 1/m. The intermittent working principle implies an unsteady onset of flow, which leads to a delay of the time frame suitable for measurements as well as to heat loads different from steady flow conditions. This work numerically simulates the starting process. It determines whether the onset of flow leads to a significant temperature rise in the model surface which in turn impacts results gathered during measurement time. The flow field in the HLB is numerically rebuilt for two operating points including valve opening. The non-stationary flow around a hyperboloid/flare configuration in the test section is calculated for one operating point including surface heating. For laminar flow it is found that due to the short duration of the starting process no significant model heating affects results obtained during measurement time.

Laminar flow transitions in a 2D channel with circular spacers

Abstract: A computational fluid dynamics (CFD) model was used to simulate the flow in a narrow spacer-filled channel, which represents the longitudinal section of a spiral-wound module membrane. The flow was computed for different geometries and Reynolds numbers. Calculations show the presence of different flow patterns in the laminar regime. Equations describing the critical Reynolds numbers at which the transition between different patterns occur were derived. It is shown that the critical Reynolds number determines the point at which good mixing conditions are achieved without excessive pressure drop.

Hydrodynamics of the flow transition from a bubble column to an airlift-loop reactor

Abstract: The hydrodynamics of an airlift-loop reactor (ALR) and a bubble column (BC) were studied in the same reactor unit. When the liquid circulation in the ALR was impeded gradually in order to obtain a BC mode of operation, there was a transition flow regime inbetween that of the ALR-type flow and the BC-type flow. In the BC the heterogeneous flow was represented by an instationary circulatory flow pattern and characterized by a liquid circulation velocity. The liquid flow in the ALR was represented by a drift-flux model. In the transition flow regime, hydrodynamic calculations based on the plug-flow behavior of an ALR appeared to be valid up to a certain defined value of the total gas-liquid flow rate. To distinguish between BC and ALR flow characteristics, a simple criterion is proposed, qualifying that the distinction between both flow patterns is determined by the superficial liquid velocity and the liquid circulation velocity. If the latter velocity exceeds the superficial liquid velocity a hydrodynamic transition will occur from a uniform ALR type of flow to a heterogeneous BC type of flow. The criterion coincides with an empirical power law function in which the liquid velocity is given as a function of the gas velocity. The values of the power-law coefficients depended on the characteristics of the two-phase flow. The change in value cohered with the onset of a change in the flow pattern.

Influence of Gravity on Two‐Layer Laminar Flow in a Microchannel

Abstract: A microchannel forms a laminar flow if the fluid velocity is sufficiently slow It is important to clarify the effect of gravity on laminar flow, since several microsystems require side-by-side laminar flow, which does not possess an interfacial tension In this work, the influence of gravity on side-by-side laminar flow was quantitatively investigated using a computational fluid dynamics (CFD) simulation As a result, a dimensionless parameter related to side-by-side laminar flow interfacial tilting was derived Using this parameter, it was possible to estimate the interfacial tilting angle The results reported here will be useful for micro-device design for chemical analysis, mixing, and chemical reactions

Effect of Co-Axial Flow Velocity on Soot Formation in a Laminar Jet Diffusion Flame under Microgravity

Abstract: To examine the effect of low co-axial flow on soot formation in a laminar jet diffusion flame, microgravity experiments have been conducted. The tested co-axial flow velocity range is 0-7.3 cm/s, which is very difficult to provide on the ground because of suffering from the additional external flow induced by buoyancy force. The result showed that the soot formation characteristics were greatly affected by co-axial flow velocity at the low flow velocity range, that is, soot concentration increased with increase in the external flow velocity. According to the radial distributions, the effect of external flow velocity on the soot formation was prominent near the outer edge of visible flame. A comparison with numerical calculation suggested that the increase of soot concentration was caused by increased flame temperature in the area of low oxygen and fuel excess region.

Evaporation of multicomponent droplets.

Abstract: Water-soluble organic compounds constitute a significant fraction of the organic atmospheric aerosol (Saxena et al, 1995) These organic compounds participate in condensation and evaporation processes in the atmosphere Therefore thermodynamic data related to aerosol formation and growth are crucially needed for developing a truly predictive capability for anthropogenic effects on eg studies of climate change Previously, evaporation rates of a series of aqueous solution droplets containing water soluble organic compounds have been determined experimentally (Riipinen et al, 2006; Koponen et al, submitted) Experimental data were incorporated into a model for multicomponent condensational growth and/or evaporation of droplets in the atmosphere (Kulmala et al, 1991) In this study we have extended our goal to make an effort to measure evaporation rates of mixed particles Our first attempt is to measure evaporation of droplet containing succinic acid and sodium chloride Using a laminar flow chamber evaporation rates of droplets at the initial size 100 nm were measured at relative humidities above their crystallization relative humidity Experiments were performed at room temperature Vapor pressures will be determined from these experiments using a mass transfer model for evaporation of binary/ternary aerosol particles A more detailed description of the measurement set up and the model is presented in the paper Riipinen et, al, 2005 In Figure 1 evaporation rates of aqueous succinic acid and succinic acid NaCl droplets as a function of time are presented The initial sizes of the droplets after DMA were 100 nm, but only data obtained inside the laminar flow reactor (1060 s) the 3 and 6 points will be used in the modeling studies For pure succinic glutaric and malonic acids experimental and modeling studies are already done (Riipinen et al, 2006 and Koponen et al, submitted) and studies of the mixtures are in progress

Influence of reactant mixing in a laminar flow reactor: The case of gas reburning. 1. Experimental study

Abstract: An experimental work of the reburn process in a laminar flow reactor with two coaxial feeding streams has been performed, with the objective of analyzing the influence of reactant mixing in this reactive system. The ways of reaching different mixing conditions have been diverse: by means of changing the velocity ratio among the two streams through which reactants are fed into the reactor, and by introducing the reactants into the reactor through different conducts (fuel introduced through the inner stream and oxidant introduced through the outer stream and vice versa). Moreover, the influence of the main variables of the reburn processaverage residence time, temperature, and stoichiometryhas been studied under laminar flow conditions. In addition, the results achieved in the present work have been compared with data from the literature obtained from experiments conducted under ideal plug-flow reactor conditions. The results show an important influence of the reactant injection mode, which affects the rea...

Hydrothermal oxidation treatment reactor: Experimental and simulated study of a non-anticipated phenomenon at the reactor inlet

Abstract: The aim of this study is to understand the thermal behaviour at the inlet of a hydrothermal oxidation reactor. This reactor was designed to eliminate charged waste water and operating in turbulent flow to limit corrosion at the injection points. Three numerical modelling were carried out to simulate the thermal behaviour of the reactor. The first program simulates the reactor operating in turbulent flow. The second one takes into account the problem of injection and the last one simulates a laminar flow with injection. Only, the program in laminar flow gives a good estimation of the thermal behaviour in the first meters of the reactor, in spite of the calculated Reynolds number which is higher than the critical one. However, in these operating conditions the flow has to be in a intermediate state. It seems that viscosity is larger than the one of pure water and the flow is laminar.

Nonlinear laminar pipe flow of fluids with strongly temperature-dependent material properties

Abstract: We study a one-dimensional model describing the laminar flow of a highly viscous fluid representing glass melt in a pipe. The flow is influenced by Lorentz force and gravity as well as temperature variation due to wall heat loss, electrical heating, advection, and heat diffusion. We take into account the full nonlinear temperature dependence of the viscosity and the electrical conductivity. For high and very low driving forces the mean velocity is found to be proportional to the forces as known from laminar pipe flow with constant material parameters. In between these two regimes, however, we identify a new flow regime. If there are no heat losses through the wall the mean velocity is proportional to the square root of the driving force. In the presence of wall heat loss the solution for the steady flow is even found to be nonunique, and to involve bifurcations for a wide range of parameters. This nonlinear behavior is shown to be a result of the closed-loop interaction between the velocity, temperature, and temperature-dependent material properties.

Growth and Motion of Heterogeneous Water Droplets in Laminar Flow Diffusion Chambers

Abstract: The growth of heterogeneous water droplets containing nanoparticles is studied in two laminar flow diffusion chambers of different designs. It is shown that the efficiency of heterogeneous condensation is, to a substantial extent, governed by the processes of heat and mass transfer inside a chamber condenser. Integral parameter C(R) representing the probability that a nanoparticle with radius R is covered with a condensate film in a laminar flow chamber is calculated. It is established that, in air-water vapor mixtures, the radius of heterogeneous water droplets may amount to several micrometers and efficient condensation begins on spherical nanoparticles when their radii exceed 5 nm.

Numerical simulation of laminar solid-liquid two-phase flow in stirred tanks

Abstract: Laminar flow of solid-liquid suspension has been rarely reported in the literature. In this article, the laminar solid-liquid two-phase flow in a lab-scale stirred tank is measured with digital particle image velocimetry (DPIV) and numerically simulated with the improved inner-outer iterative method. The simulation results show good agreement with the present data. In the range of low solid volume concentration under investigation, solid particles have minor impact on two-phase flow, and the simulated flow fields of both phases are similar to the counterpart of single-phase laminar liquid flow. The comparison of simulation with experiments of single-phase laminar flow shows reasonable agreement. These observations suggest that the numerical method employed in the present study is reliable for analysis of stirred tanks. The influence of impeller off-bottom clearance on velocities is found significant: the lower the impeller, the smaller the radial and axial velocities, and the higher the solid concentration.

Effect of periodical injection for the intensification of mixing process

Abstract: Effect of periodical injection of branching flows perpendicular to the laminar main flow is investigated experimentally and numerically. The periodical injection forms a regular alternative layer of main flow fluid and branching flow fluid. The boundary between main flow fluid and the branching flow fluid is stretched and folded by the parabolic laminar velocity profile in the main flow. The importance of the duty ratio of the branching flow injection, the number of branching flows and the phase of branching flows are discussed.

Laminar Diffusion Flame in the Reacting Mixing Layer

Abstract: Laminar flows in which mixing and chemical reactions take place between parallel streams of reactive species are studied numerically. The governing equations for laminar flows are from two-dimensional compressible boundary-layer equations. The relevant chemistry is a finite rate single step irreversible reaction with Arrhenius kinetics. Ignition, premixed flame, and diffusion flame regimes are found to exist in the laminar reacting mixing layer at high activation energy. At high Mach numbers, ignition occurs earlier due to the higher temperatures in the unburnt gas. In diffusion regimes, property variations affect the laminar profiles considerably and, thus, need to be included when there are large temperature differences. The maximum temperature of a laminar reacting mixing layer is in the almost linear relationship with the adiabatic flame temperature at low heat release, but is only weakly linearly-correlated at high heat release.

Modeling and Design of a New Type Air Mass Flow Sensor

Abstract: Air mass flow sensor is based upon thermal conduction and convection,provided the laminar flow conditions prevail in the whole measurement range.Due to the turbulence in the manifold,an especially small channel has been designed inside the manifold,and the laminar flow condition has been maintained throughout the measurement range in this small channel.The velocity distribution throughout the channel has been predicted.An ideal Re≈12~110 is obtained throughout the small channel.A fixed velocity ratio between the flow in whole manifold and in small channel is obtained.The air intake will be obtained though measuring the flow rates in the small channel.At the constant temperature of heater,temperature field around the heater under different flow conditions were simulated by finite volume method(FVM).The relationships of dt,the measuring distance and flow rate are obtained.There is the highest dt for increasing of the measurement distance,and the corresponding measurement distance is 140～210 m.By placing two pairs of thermistors,the highest precision of flow velocity can reach 0.02 m/s.

Method and apparatus for improving radial flow moving bed regeneration/reaction system performance

Abstract: An improved radial or cross flow moving bed regenerator or reactor, in which the solid particle residence time in the vessels can be changed in different section of the regenerator or reactor. The improvement results from the placement of one or multiple screen inserts which divides the radial or cross flow bed into separate solid flow channels. The residence time of the solid in each solid flow channels are optimized based on the regeneration or reaction requirement by changing the location, orientation and geometry of the screen inserts. As a result of the optimization of solid residence time in different section in the radial flow bed, the efficiency of a regenerator or a reactor is improved.