Showing papers on "Laminar flow reactor published in 2009"

NO PLIF Study of Hypersonic Transition Over a Discrete Hemispherical Roughness Element

Abstract: Nitric oxide (NO) planar laser-induced fluorescence (PLIF) has been use to investigate the hypersonic flow over a flat plate with and without a 2-mm (0.08-in) radius hemispherical trip. In the absence of the trip, for all angles of attack and two different Reynolds numbers, the flow was observed to be laminar and mostly steady. Boundary layer thicknesses based on the observed PLIF intensity were measured and compared with a CFD computation, showing agreement. The PLIF boundary layer thickness remained constant while the NO flowrate was varied by a factor of 3, indicating non-perturbative seeding of NO. With the hemispherical trip in place, the flow was observed to be laminar but unsteady at the shallowest angle of attack and lowest Reynolds number and appeared vigorously turbulent at the steepest angle of attack and highest Reynolds number. Laminar corkscrew-shaped vortices oriented in the streamwise direction were frequently observed to transition the flow to more turbulent structures.

Pilot Scale Two-phase Continuous Flow Biodiesel Production via Novel Laminar Flow Reactor−Separator

Abstract: The following study presents the first quantitative performance data for a novel laminar flow biodiesel reactor/separator. The reactor ideally achieves high conversion of vegetable oil triglycerides to biodiesel while simultaneously allowing glycerol to phase separate and settle from the reacting flow. The reactor was operated using pretreated waste canola oil as a feedstock; potassium hydroxide dissolved in methanol was used as a catalyst. Reactor performance was assessed by computing conversion of vegetable oil triglycerides to biodiesel as well as subsequent separation of the coproduct glycerol stream. At slightly elevated temperatures (40−50 °C), an overall feed of 1.2 L/min, a 6:1 molar ratio of methanol to vegetable oil triglycerides, and a 1.3 weight % catalyst loading, the reactor was able to achieve greater than 99% conversion of pretreated waste canola oil to biodiesel and remove 70−99% of glycerol produced.

Conjugate Heat and Mass Transfer from a Drying Rectangular Cylinder in Confined Air Flow

Abstract: Heat and mass transfer from a porous body subject to convective drying is investigated numerically based on Luikov's equations The air flow is assumed incompressible, two-dimensional, laminar, confined in a channel, and parallel to the rectangular-shaped solid The finite-volume method is used and the computed temporal and spatial variations of moisture content, temperature, concentration, and flow parameters for two different flow rates are analyzed Two flow configurations are studied: with and without a flow divider upstream of the cylinder in an attempt to eliminate the presence of separation zones and study their effect on drying It was found that such effects may greatly affect the drying process, along with frontal area stagnation and the thickness of the body

Optical Coal Particle Temperature Measurement under Oxy‐Fuel Conditions: Measurement Methodology and Initial Results

Abstract: Coal combustion under oxy-fuel conditions shows significant differences to combustion in air. Examinations on the single-grain level give detailed insight into the combustion phenomena of ignition, volatile combustion, and char burnout and, therefore, provide the fundamentals for the development of large-scale oxy-fuel facilities. The combustion of a hard coal in a size fraction of d p = 90-125 μm was investigated in a laminar flow reactor at a temperature of 1500 K. The gaseous fuel oxidizer contained 3 % O 2 by volume and CO 2 or N 2 as diluents. A third measurement in a CO 2 -rich atmosphere containing 9 % O 2 is also presented to show the influence of O 2 concentration. Particle temperatures were measured for three residence times with an imaging two-color pyrometer.

Numerical Modeling of Laminar Pulsating Flow in Porous Media

Abstract: The laminar pulsating flow through porous media was numerically studied. Two-dimensional flows in systems composed of a number of unit cells of generic porous structures were simulated using a computational fluid mechanics tool, with sinusoidal variations in flow with time as the boundary condition. The porous media were periodic arrays of square cylinders. Detailed numerical data for the porosity ranging from 0.64 to 0.84, with flow pulsation frequencies of 20-64 Hz were obtained. Based on these numerical data, the instantaneous as well as the cycle-average permeability and Forchheimer coefficients, to be used in the standard unsteady volume-averaged momentum conservation equation for flow in porous media, were derived. It was found that the cycle-average permeability coefficients were nearly the same as those for steady flow, but the cycle-average Forchheimer coefficients were significantly larger than those for steady flow and were sensitive to the flow oscillation frequency. Significant phase lags were observed between the volume-averaged velocity and the pressure waves. The phase difference between pressure and velocity waves, which is important for pulse tube cryocooling, depended strongly on porosity and the mean-flow Reynolds number.

Simulation of the Two-Phase Flow Hydrodynamics in an IRDE Reactor

Abstract: Many industrial processes deal with gas bubbles, e.g., the chlor-alkali processes or a side reaction in metal deposition reactions. It is therefore very important to describe the influence of gas bubbles on the fluid flow in a quantitative way. In the present paper, the two-phase flow is both experimentally characterized and numerically modeled in a reactor with a rotating flow field such as the inverted rotating disk electrode (IRDE). Polarization curves of the hydrogen evolution in 0.1 M Na 2 SO 4 at pH 2.5 are recorded at different rotation speeds. The bubble dispersion and size distribution of the hydrogen bubbles are determined by laser marked shadowgraphy and interferometric laser imaging for droplet sizing. Concerning the numerical investigations, in the first step the single-phase flow solution in the vicinity of the IRDE is compared to the analytical solution of the flow field, as proposed by Cochran [Proc. Cambridge Philos. Soc., 30, 365 (1934)]. In the following step, an Eulerian-Lagrangian two-phase flow model is used to track the bubbles. Two-way momentum coupling effects between bubbles and electrolyte flow are taken into account. The calculated two-phase flow field compares well against the experimental data of the two-phase flow field obtained from the optical imaging techniques.

Modelling of laminar flow in the inlet section of rectangular microchannels

Abstract: This paper is a study of laminar flow in rectangular microchannels. The behaviour of compressible and incompressible fluids in microchannels was simulated using CFD software. Numerical data were compared to experimental measurements to test the validity of CFD models. The velocity profile of flow developing inside the channel is described as a function of the Reynolds number Re, varying from 100 to 2000, and the aspect ratio h/w, ranging from 1 to 0.125. The fundamental importance of the entrance length of microchannels is highlighted. Numerical data were applied to define analytical formulae covering the minimum entrance length for fully developed laminar flow of compressible fluids, viscous stress and incremental pressure drop effect during flow development, and the velocity profiles of flow for compressible and incompressible fluids.

Three-dimensional CFD model for a flat plate photocatalytic reactor: Degradation of TCE in a serpentine flow field

Abstract: Computational fluid dynamics (CFD) simulation was applied to a photocatalytic reactor with surface reaction for trichloroethylene (TCE) oxidation at various pollutant concentrations, and flow rates. First-order and Langmuir-Hinshelwood kinetics for TCE removal rate were considered. The results were compared with those from experiments of Demeestere et al. (Appl Catal B Environ. 2004;54:261–274) in a flat plate photocatalytic reactor with serpentine geometry. The flow regime was laminar. Through the CFD simulation, the velocity field and the concentration gradient of TCE in the reactor were studied in detail. At Reynolds numbers around 900, the laminar flow becomes unstable. Under such a condition, when flow passes the 180° sharp turns, due to formation of secondary flow and consequently vortices, there is a lot of cross-sectional mixing in the reactor. This kind of studies can help us to model the photocatalytic reactor as accurately as possible. © 2008 American Institute of Chemical Engineers AIChE J, 2009

Photocatalytic Reactor Employing Titanium Dioxide: From a Theoretical Model to Realistic Experimental Results

Abstract: The performance of a reacting system for degradation of trichloroethylene (TCE) in a pilot-size annular photocatalytic reactor having a tubular lamp located at its centerline was studied. The reactor operation was carried out with commercial catalytic particles of titanium dioxide (Aldrich) in a water suspension. The description of the reactor performance was made by employing a kinetic model developed in a laboratory reactor of different size and configuration, irradiated with similar lamps of lower output power. The annular reactor was operated in the continuous mode but inside the loop of a recirculation system.The performance of the annular reactor was modeled by assuming three different behaviors: (i) a well-stirred tank reactor, (ii) a pseudo-steady-state laminar flow reactor in a batch recycle, and (iii) a transient-state laminar flow reactor in a recycle. Case iii produced the best representation of the experimental data. Along with the experimental validation of the developed theoretical models, ...

Hydrodynamics in Sulzer SMX Static Mixer with Air/Water System

Abstract: A Sulzer static mixer with SMX internal structure is investigated for its performance with respect to flow behavior, gas hold-up, and mass transfer rates in an air/water system. The reactor consist...

Analysis of Laminar Flow in the Entrance Region of Parallel Plate Microchannels for Slip Flow

Abstract: Microscale fluid dynamics has received intensive interest due to the emergence of microelectromechanical systems (MEMS) technology. Fluid flow in microdevices has some characteristics which one of them is rarefaction effect related with gas flow. In this work, the steady state laminar rarefied gas flow in the entrance region of parallel plate microchannels is investigated by the integral method with slip flow conditions at solid surface. The effects of Knudsen number on friction factor and Nusselt number are presented in graphical form as well as analytical form. Also the effect of Knudsen number on hydrodynamic entry length is presented. The results show that as Knudsen number increases the local friction factor and Nusselt number decrease. Also an increment of Knudsen number leads to a larger amount of hydrodynamic entry length.Copyright © 2009 by ASME

Relation between the Friction Coefficient and Re Number for Spherical Capsule Train-Water Flow in Horizontal Pipes

Abstract: This experimental study investigated flow regimes of a spherical capsule train-water flow in horizontal pipes The density of spherical capsules (made of polypropylene, s = 087) is close to that of ice (s = 082) The Re number of transition from laminar to turbulent flow for single-phase water in straight pipes is approximately 2300; the experiments indicate that the Re number of transition from laminar to turbulent flow for the two-phase flow of the spherical capsule-water is around 25000 The reduced Re number that explains the capsule concentration effect on transition Re number was defined New correlations of the friction coefficient were formed based on Rered The new correlations for the three flow zones are: laminar zone, ; transition zone, ; and turbulence zone, Friction factor correlations were used for calculating the pressure gradient (in the Darcy-Weisbach equation) for hydraulically smooth pipes (with an average deviation of 656%)

Sandwich mixer–reactor: influence of the diffusion coefficient and flow rate ratios

Abstract: A sandwich mixer consists of mixing two solutions in a channel, one central laminar flow being sandwiched between two outer flow solutions. The present numerical study considers the convection-diffusion of two reacting species A and B, provided respectively by the two incoming solutions. The simulations show how the diffusion coefficient, flow rate and species concentration ratios influence, via the transversal diffusion length and reaction kinetics, the reaction extent at the end of the sandwich mixer. First, this extent can be enhanced up to 60% if the species with the lowest diffusion coefficient is located in the outer solutions where the flow velocity is small compared to that of the central part (higher residence time). Secondly, decreasing the outer flow rates (to confine the reaction close to the walls) and increasing the local concentration to keep the same flux ratio improve the extent by 300%. Comparison with a bi-lamination passive mixer, with an ideal mixer and an electro-osmotic driven flow mixer is presented. These conclusions are also demonstrated for consecutive reactions, showing an amplification of the effects described above. The results are also presented versus the residence time in the mixer-reactor to show the time window for which the gain is appreciable.

Modeling Oxidation of Soot Particles Within a Laminar Aerosol Flow Reactor Using Computational Fluid Dynamics

Abstract: This work examines the measurement of surface specific soot oxidation rates with the High Temperature Oxidation-Tandem Differential Mobility Analyzer (HTO-TDMA) method. The Computational Fluid Dynamics package CFD-ACE+ is used to understand particle flow, oxidation and size dependent particle losses in the laminar aerosol flow reactor using an Eulerian-Lagrangian framework. Decrease of DMA selected mono-disperse particle size distribution due to oxidation within the aerosol tube is modeled using fitted kinetic soot oxidation parameters. The effects of Brownian diffusion and thermophoresis on particle flow and loss to the reactor walls are evaluated. The position of peak particle diameter, which is used as an indicator to determine oxidation rate, is found to be independent of diffusion, thermophoresis and secondary flow effects, thus validating its use in deriving kinetic soot oxidation parameters. Diffusion does not affect the evolution of particle size distribution within the reactor. However, thermopho...

Simple Models for Laminar Thermally Developing Slug Flow in Non-Circular Ducts and Channels

Abstract: Solutions to the classical Graetz slug or plug flow problem in non-circular ducts are examined. These solutions have applications where a constant uniform velocity distribution exists across a channel or duct. These are most often realized in the laminar flow of low Prandtl number liquids, such as liquid metals, and low Reynolds number flows through porous media. Expressions are developed for a number of applications using the asymptotic correlation method of Churchill and Usagi. These expressions vary depending on the definition used for the dimensionless heat transfer coefficient in the case of constant wall temperature boundary condition (T), and the dimensionless wall temperature for the constant flux boundary conditions, (H) and (H1). Finally simple expressions are developed for predicting the thermal entrance length and fully developed flow Nu values for non-circular ducts.Copyright © 2009 by ASME

The Role of NO and NO2 in Partial Oxidation of Methane

Abstract: NOx is well known to be a promoter in the oxidation of hydrocarbons. The role of NO and NO2 depends on the reaction conditions including pressure, mixture strength (fuel- lean/rich mixtures), and temperature. The present work aims to identify the individual effect of small amounts (1000 ppm) of NO and NO2 on the partial oxidation of methane in a laminar flow reactor under elevated pressure conditions up to 1 MPa. It was found that the addition of NOx reduced the initiation temperature by approximately 15oC. The promoting effect of NOx, which was considerably less at elevated pressures than at atmospheric pressure as observed previously, is proposed to result from a cycling process of inter-conversion between NO and NO2. In the fuel-rich conditions used in the present work, NO2 serves as a reaction initiator (CH4 + NO2 →CH3 + HNO2), while NO acts to transform relatively less reactive species (such as CH3O2 , HO2 ) into their more reactive counterparts (CH3O, OH ), thus speeding up the overall reaction process. It may be noted that this contrasts with certain low pressure oxidising conditions, where NO has a much greater accelerating effect than NO2. The oxidation of NO to NO2 is extremely fast under the high pressure conditions and in the presence of O2 as used in this work. Hence, under the conditions of this study, co-feeding of NOx, either as NO or NO2, produced a similar accelerating effect.