Showing papers on "Laminar flow reactor published in 2012"

Numerical study on the effects of diluents on the laminar burning velocity of methane-air mixtures

Abstract: The effect of diluents on the laminar burning velocity of the premixed methane–air–diluent flames was numerically studied using the Chemkin package. The mechanisms of dilution, thermal-diffusion, and chemical effects of diluents on the laminar burning velocity were analyzed quantitatively at different dilution ratios for different diluents. Results show that the laminar burning velocity is decreased in the order from helium, argon, nitrogen, and carbon dioxide. In the case of N2, the thermal-diffusion and chemical effects can be negligible and the decrease of the laminar burning velocity is largely caused by the dilution effect. The dilution, thermal-diffusion, and chemical effects of CO2 suppress the laminar burning velocity, where the dilution effect plays a dominant effect among them. For helium and argon diluents, the chemical effect can be negligible and the thermal-diffusion effect enhances the laminar burning velocity. Therefore, the dilution effect has a much larger suppression effect on decreasin...

Non-ideal flow in an annular photocatalytic reactor

Abstract: The objective of the present work was to analyze the effect of different flow modes on the performance of the photocatalytic reactor used for purification of air. For this purpose photocatalytic oxidation of toluene was used as the model reaction. Photocatalytic reactor was operated in two different flow modes: classic type of an annular reactor with basically ideal (plug) flow with some extent of dispersion (reactor A) and annular flow reactor acted as stirred tank reactor with mixing of reaction mixture accomplished by recirculation (reactor B). The present work comprises two sections. In the first one, hydrodynamics inside the reactor without presence of the chemical reaction is examined. Stimulus- response technique was applied and some flow models were tested to describe real fluid flow through the reactors. It was found that the axial dispersion model fits well the response data for reactor A. Flow through the reactor B is well described by the simple model of ideal mixing with the mean residence time as adjustable parameter. Also, the CFD modeling results indicated the non-uniform flow distribution in the both actual annular reactors, especially in the entrance region. The second part of paper deals with investigation of the photocatalytic oxidation at various reaction conditions and performed in two different reactor configurations (reactor A and B). Several reactor models are applied, such as one dimensional (1D) model of tubular reactor at the steady state conditions, axial dispersion model at non-stationary conditions and the model of the continuous non-stationary stirred tank reactor. Numerical methods necessary for solving model equations and parameter estimation were described. Finally, the validation procedure for the all models used in this study was presented and the obtained results are discussed.

Numerical Investigation on Laminar Microconvective Liquid Flow With Entrance Effect and Graetz Problem due to Variation in Thermal Properties

Abstract: This work deals with the analysis of forced convection in single-phase laminar flow of liquid through microsized circular geometry with a diameter of 100 × 10−6 m. The problem with hydrodynamically and thermally developing flow in the entrance region with no-slip, no-temperature jump and constant wall heat flux boundary condition is numerically studied. Two-dimensional (with axisymmetry) simulation is carried out to understand the effect of fluid property variations on flow development and heat transfer. Pure continuum-based governing equations are solved to predict the significance of momentum and energy transport due to temperature-dependent viscosity and thermal conductivity variation, respectively. The radial inward flow is induced due to temperature-dependent density variation that sharpens the axial velocity profile. The investigation also analyzes the change in Nusselt number with locations in the channel for Graetz problem with uniform heating condition. The flattening of axial velocity profile, r...

Microwave plasma torch generating laminar flow for materials processing

Abstract: A microwave plasma torch providing two laminar flows is described. Two laminar flows are created using a set of at least three concentric, staggered dielectric tubes connected to a pressurized gas source. An inner laminar flow entrains injected particles entering the plasma. An outer laminar flow creates a sheath around the plasma and prevents it from attaching to the walls of the plasma torch. The entry point of the gas source is designed to ensure laminar flow for both the entrainment of the particles and for the shielding of the plasma plume. The uniform processing conditions results in uniform particles and a homogenous materials distribution. This enables a final product with improved thermal properties, improved corrosion and wear resistance and a higher tolerance to interface stresses. The microwave plasma torch can be used for producing nanomaterial powder and for spray coating materials onto various substrates.

Steady Laminar Axisymmetrical Nozzle Flow at Moderate Reynolds Numbers: Modeling and Experiment

Abstract: Flow through an axisymmetrical parameterized contraction nozzle of limited size with area contraction ratio 21.8 and total length 6 cm is studied for moderate Reynolds numbers 300 3000 to Re> 1000. Therefore, the studied contraction nozzle is of use for applications requiring a small nozzle with known low turbulence flow at the exit such as moderate Reynolds number free jet studies or bio fluid mechanics (respiration, speech production,...) and the flow at the exit of the nozzle can be accurately described by a simple boundary layer algorithm for Re> 1000. [DOI: 10.1115/1.4005690]

Residence Time Distribution Models Derived from Non‐Ideal Laminar Velocity Profiles in Tubes

Abstract: The theoretical E-curve for the laminar flow of non-Newtonian fluids in circular tubes may not be accurate for real tubular systems with diffusion, mechanical vibration, wall roughness, pipe fittings, curves, coils, or corrugated walls. Deviations from the idealized laminar flow reactor (LFR) cannot be well represented using the axial dispersion or the tanks-in-series models of residence time distribution (RTD). In this work, four RTD models derived from non-ideal velocity profiles in segregated tube flow are proposed. They were used to represent the RTD of three tubular systems working with Newtonian and pseudoplastic fluids. Other RTD models were considered for comparison. The proposed models provided good adjustments, and it was possible to determine the active volumes. It is expected that these models can be useful for the analysis of LFR or for the evaluation of continuous thermal processing of viscous foods.

Two‐dimensional model of methane thermal decomposition reactors with radiative heat transfer and carbon particle growth

Abstract: A two-dimensional model of methane thermal decomposition reactors is developed which accounts for coupled radiative heat and polydisperse carbon particle nucleation, growth, and transport. The model uses the Navier–Stokes equations for the fluid dynamics, the radiative transfer equation for methane and particle species radiation absorption, the advection–diffusion equation for gas and particle species transport, and a sectional method for particle species nucleation, heterogenous growth, and coagulation. The model is applied to a tubular laminar flow reactor. The simulation results indicate the development of a reaction boundary layer inside the reactor, which results in significant variation of the local particle size distribution across the reactor. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2545–2556, 2012

Numerical simulation of incompressible laminar flow in a three-dimensional channel with a cubical open cavity with a bottom wall heated

Abstract: A three-dimensional numerical simulation study for both laminar steady and unsteady regimes has been carried out for the mixed convective flow over a three-dimensional cubical open cavity. The cavity is heated from below at constant temperature while the other walls are adiabatic. The numerical simulation has been done using a three-dimensional incompressible finite volume flow solver. The effects over the velocity and temperature distribution of the buoyancy forces acting perpendicular to the mainstream flow are studied for Reynolds numbers (Re) between 100 and 1500; Prandtl number (Pr) is set to 0.7 and Richardson number (Ri) between 10?3 to 101. The phenomenological description of the mixed convection inside and outside the cavity and the combined effects of the natural and forced convection have been obtained. For both high Re and Ri the flow becomes unsteady. The mixed convection effects dominate the flow transport mechanism and push the recirculation zone and the flow further upstream.

A differential pressure laminar flow reactor supports osteogenic differentiation and extracellular matrix formation from adipose mesenchymal stem cells in a macroporous ceramic scaffold.

Abstract: We present a laminar flow reactor for bone tissue engineering that was developed based on a computational fluid dynamics model. The bioreactor design permits a laminar flow field through its specific internal shape. An integrated bypass system that prevents pressure build-up through bypass openings for pressure release allows for a constant pressure environment during the changing of permeability values that are caused by cellular growth within a porous scaffold. A macroporous ceramic scaffold, composed of zirconium dioxide, was used as a test biomaterial that studies adipose stem cell behavior within a controlled three-dimensional (3D) flow and pressure environment. The topographic structure of the material provided a basis for stem cell proliferation and differentiation toward the osteogenic lineage. Dynamic culture conditions in the bioreactor supported cell viability during long-term culture and induced cell cluster formation and extra-cellular matrix deposition within the porous scaffold, though no complete closure of the pores with new-formed tissue was observed. We postulate that our system is suitable for studying fluid shear stress effects on stem cell proliferation and differentiation toward bone formation in tissue-engineered 3D constructs.

CFD simulation of microscale flow field in spiral groove dry gas seal

Abstract: The three dimension micro-scale flow field in spiral groove dry gas seals(S-DGS) is simulated by using CFD software based on gas lubrication theory in this article. Effect of gas flow state on the Seal performance is analyzed under different gas film thickness. Laminar model and k-e turbulent model are used separately to obtain the open force, leakage rate. The results show that gas pressure distribution is in well agreement with reference. The turbulence effect of gas film can enhance the hydrodynamic effect and hence enlarge the open force, while decrease the leakage rate of seal.

Parameterization of Laminar Burning Velocity Dependence on Pressure and Temperature in Hydrogen/Air/Steam Mixtures

Abstract: A new correlation describing the laminar burning velocity of hydrogen/air mixtures as a function of temperature, pressure, and mixture composition is proposed. The correlation is developed for reactive hydrogen/air mixtures diluted with steam for wide temperature, pressure, and composition ranges. The study includes the following stages: first, the laminar burning velocity was calculated with the detailed reaction mechanism of Maas and Warnatz (1988) implemented in the code INSFLA; second, the results obtained were validated against experimental data and a new heuristic approximation based on them was created. The correlation found consists of simple mathematical expressions and provides a good approximation of the laminar burning velocity in the range between 200 K and 600 K for temperature, between 0.1 bar and 10 bar for pressure, and up to 20 mol% steam dilution.

Flow modeling in electrochemical tubular reactor containing volumetric electrode: Application to copper cementation reaction

Abstract: The aim of the present work is to study the electrolyte flow characteristics in a tubular reactor containing a volumetric electrode, acting as turbulence enhancer, applied in our previous works to copper removal by cementation process. The hydrodynamic behavior of the electrolyte within the reactor under study has been determined using the residence time distribution (RTD) experimentally determined by a pulse tracer technique. The results obtained have shown a strong influence of the presence or absence of the volumetric electrode inside the reactor in the hydrodynamic behavior. It is found by RTD measurements the existence of dead volume in the reactor under some conditions which decrease with increasing of volumetric electrode mass. The active and a dead volume of the reactor are quantified at different masses of a volumetric electrode (0 g, 10 g and 20 g) and at different flow rates (1 L/min, 2 L/min, 3 L/min and 5 L/min). The experimental curves of exit distribution function E ( t ) at various operating conditions are analyzed and some experimental parameters are determined like the mean residence time t s and the variance of the response data σ 2 . To model the reactor studied, an industrial software package “DTS.PRO 4.2” for process modeling was used. It was found that the reactor is an arrangement of simple ideal reactors; it is composed of one plug flow reactor followed by three stirred tanks in series. The model simulations were validated with the experimental observations in the case of cementation reaction.

A fundamental analysis of continuous flow bioreactor and membrane reactor models with tessier kinetics

Abstract: In this research we analyze the steady-state operation of a continuous flow bioreactor, with or without recycle, and an idealized or nonidealized continuous flow membrane reactor. The model extends to include a fixed bed reactor where a fraction of the biomass is detached by the flow. The reaction is assumed to be governed by Tessier growth kinetics. We show that a flow reactor with idealized recycle has the same performance as an idealized membrane reactor and that the performance of a nonidealized membrane reactor is identical to that of an appropriately defined continuous flow bioreactor with nonidealized recycle. The performance of all three reactor types can therefore be obtained by analyzing a flow reactor with recycle. The steady states of the recycle model are found and their stability determined as a function of the residence time. The performance of the reactor at large residence times is obtained.

Investigations on hydrodynamics of multilayer Π-type radial flow reactors

Abstract: Consisting of two or three different layers of catalyst or adsorbent, the multilayer radial flow reactor is a novel radial reactor with compact structure and high performance. In this article, pressure profiles in the flow channels and layers of a three-layer radial flow reactor were measured and the properties of the fluids in the flow channels and layers were investigated. Results show that the uniformity of the pressure profiles in the distributing and collecting channels in the axial direction has a significant effect on the flow distribution of each layer. The uniformity of the flow distribution in multilayer Π-type radial flow reactors varies in the radial direction. It is better in the outer layer than in the inner layer when the pressure variation in the center channel is more significant than that in the annular channel. The main contributions of this work are helpful to the proper design and optimum operation of the multilayer radial reactor. Copyright © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.

CFD simulation of Taylor–Couette flow in scraped surface heat exchanger

Abstract: The flow between two concentric cylinders which is termed as Taylor–Couette flow has been studied in scraped surface heat exchanger with and without blades. Shear rate in annular flow with and without blades was measured by Dumont et al. (2000a) using electrochemical method and determined the onset of Taylor vortices at specific Taylor number in both cases for Newtonian flow. CFD simulations have been carried out to determine the transition zone from laminar Couette flow to Taylor vortex flow using the same geometry for which Dumont et al. (2000a) had carried out the experiments. The Reynolds stress model (RSM) and k – ɛ model are used for Taylor vortex flow ( Ta > 300) to characterize the flow pattern in annular flow and SSHE respectively. The aim of the present work is to analyze the effect of rotating scraper on the existing flow patterns in simple annular flow using CFD simulations.

RTD Studies in Plug Flow Reactor and its Simulation with Comparing Non Ideal Reactors

Abstract: This paper proposes RTD studies in plug flow reactor and comparison of non-ideal reactors using residence time distribution function. The model also gives a prediction of the number of ideal continuous stirred tank reactors (CSTR) that could represent the non-ideal plug flow reactor (PFR) in question. Simulated results reveal that 10 numbers of ideal stirred tanks in series would represent the non-ideal plug flow reactor under study. The graphical result of all four reactors is generated directly by polymath. Most of the chemical reactors in the industries have non-ideal regime. The non-ideal plug flow reactor (PFR) is one whose attributes deviate from that of the ideal plug flow reactors. Therefore, an in-depth knowledge of the residence time distribution (RTD) of components in the reactor is necessary for its analysis. The residence time distribution indicates how much time each fraction of a charged material spends in the vessel. The residence time distribution of reactants or tracers in a flow vessel is a key datum for determining reactor performance.