Showing papers on "Laminar flow reactor published in 2000"

An experimental and modeling investigation of particle production by spray pyrolysis using a laminar flow aerosol reactor

Abstract: The influence of operating parameters on the morphology of particles prepared by spray pyrolysis was investigated using a temperature-graded laminar flow aerosol reactor Experimentally, zirconia particles were prepared by spray pyrolysis using an aqueous solution of zirconyl hydroxide chloride Hollow particles were formed if the reactor temperature was high, the temperature gradient was too large, the flow rate of carrier gas was high, and the initial solute concentration was low A numerical simulation of the pyrolysis process was developed using a combination of two previous models The simulation results compared well with the experimental results

Hydrolysis of N2O5 on submicron sulfuric acid aerosols

Abstract: The kinetics of reactive uptake of gaseous N2O5 on submicron sulfuric acid aerosol particles has been investigated using a laminar flow reactor coupled with a differential mobility analyzer (DMA) t...

Unsteady Laminar Duct Flow With a Given Volume Flow Rate Variation

Abstract: In this paper we give a procedure to obtain analytical solutions for unsteady laminar flow in an infinitely long pipe with circular cross section, and in an infinitely long twodimensional channel, created by an arbitrary but given volume flow rate with time. In the literature, solutions have been reported when the pressure gradient variation with time is prescribed but not when the volume flow rate variation is. We present some examples: (a) the flow rate has a trapezoidal variation with time, (b) impulsively started flow, (c) fully developed flow in a pipe is impulsively blocked, and (d) starting from rest the volume flow rate oscillates sinusoidally. [S0021-8936(00)01702-5]

Direct numerical simulation of flow separation behind a swept, rearward-facing step at ReH=3000

Abstract: The effect of sweep on a transitional separation bubble behind a backward-facing step is investigated using direct numerical simulation (DNS). The Reynolds number based on step height and free stream component normal to the step, Reα=(HC∞ cos α)/ν, is kept constant at 3000 for sweep angles α between 0° and 60°. Results agree well with two experimental investigations. Up to α=40°, the mean flow follows the sweep-independence principle. For higher sweep angles, the size of the separated flow region is shortened considerably which is mainly due to an upstream shift of transition in the laminar shear layer emanating from the step and—to a lesser degree—to an increase in turbulent momentum flux uv¯. Fluctuations of wall-stress and wall pressure are largest near the reattachment location and their magnitude scales with (C∞ cos α)2 for all sweep angles. Transition is dominated by a Kelvin–Helmholtz-type instability of the free shear layer. The influence of skewing on the growth rate of instability waves is weak ...

Mixing Performance by Reciprocating Disk in Cylindrical Vessel

Abstract: Experiments on mixing performance have been carried out by reciprocating a disk in a cylindrical vessel. The force acting on the disk was measured by a force transducer installed between the impeller shafts, and the disk position was detected by a photo interrupter. With increasing reciprocating Reynolds number, the dimensionless maximum force acting on the disk decreases in inverse proportion to the Reynolds number in laminar creeping flow and becomes almost constant in turbulent flow. The Lissajous figure of force and disk position during reciprocation is deformed from an ellipsoid to an inclined parallelogram as the flow changes from laminar to turbulent. The average power is obtained by integrating the product of force and disk velocity during one cycle. The power number can be correlated with the reciprocating Reynolds number in a similar way to correlating the maximum force. The mixing process was visualized by using the decolorizing reaction, based on which the flow behavior could be divided into three patterns; laminar creeping flow without vortex generation, laminar flow with generation of a vortex which dissipates within a half cycle of reciprocation, and turbulent flow with vortexes. The mixing process is extremely slow in laminar creeping flow. It is promoted by stretching and folding of fluid lumps in the flow with vortex generation. The dimensionless mixing time was investigated in terms of the power input per unit volume of liquid. In turbulent flow, the mixing time is considerably smaller than that required for ordinary rotating mixing.

Wall effects of laminar hydrogen flames over platinum and inert surfaces

Abstract: Different aspects of wall effects in the combustion of lean, laminar and stationary hydrogen flames in an axisymmetric boundary-layer flow were studied using numerical simulations with the program ...

Hydrodynamic suppression of soot formation in laminar coflowing jet diffusion flames

Abstract: Effects of flow (hydrodynamic) properties on limiting conditions for soot-free laminar non-premixed hydrocarbon/air flames (called laminar soot-point conditions) were studied, emphasizing non-buoyant laminar coflowing jet diffusion flames. Effects of air/fuel-stream velocity ratios were of particular interest; therefore, the experiments were carried out at reduced pressures to minimize effects of flow acceleration due to the intrusion of buoyancy. Test conditions included reactant temperatures of 300 K; ambient pressures of 3.7-49 8 kPa; methane-, acetylene-, ethylene-, propane-, and methane-fueled flames burning in coflowing air with fuel-port diameters of 1.7, 3.2, and 6.4 mm, fuel jet Reynolds numbers of 18-121; air coflow velocities of 0-6 m/s; and air/fuel-stream velocity ratios of 0.003-70. Measurements included laminar soot-point flame lengths, laminar soot-point fuel flow rates, and laminar liftoff conditions. The measurements show that laminar soot-point flame lengths and fuel flow rates can be increased, broadening the range of fuel flow rates where the flames remain soot free, by increasing air/fuel-stream velocity ratios. The mechanism of this effect involves the magnitude and direction of flow velocities relative to the flame sheet where increased air/fuel-stream velocity ratios cause progressive reduction of flame residence times in the fuel-rich soot-formation region. The range of soot-free conditions is limited by both liftoff, particularly at low pressures, and the intrusion of effects of buoyancy on effective air/fuel-stream velocity ratios, particularly at high pressures. Effective correlations of laminar soot- and smoke-point flame lengths were also found in terms of a corrected fuel flow rate parameter, based on simplified analysis of laminar jet diffusion flame structure. The results show that laminar smoke-point flame lengths in coflowing air environments are roughly twice as long as soot-free (blue) flames under comparable conditions due to the presence of luminous soot particles under fuel-lean conditions when smoke-point conditions are approached. This is very similar to earlier findings concerning differences between laminar smoke- and sootpoint flame lengths in still environments.

Heat transfer by laminar flow in a vertical pipe with twisted-tape inserts

Abstract: Heat transfer for laminar flow of water in an air-cooled vertical copper pipe with four twisted-tape inserts was determined experimentally. The tests were executed for laminar flow within 110 ≤ Re ≤ 1500, 8.1 ≤ Gz ≤ 82.0 and 1.62 ≤ y ≤ 5.29. The correlation equation for heat transfer was defined for the tested range. The obtained results were compared to the results of other authors.

Complex Flow and Gas-Phase Reactions in a Horizontal Reactor for GaN Metalorganic Vapor Phase Epitaxy

Abstract: Three-dimensional fluid simulations are performed in a horizontal reactor for GaN epitaxy. Attention is paid to the effect of gas flow velocity at the inlet and gas pressure. It is found that the gas flow rate rather than the velocity or the pressure is a key parameter which controls the spatial distribution of streamlines, temperature and gas-phase species. As the gas flow rate increases, the size of return-flow or flow-separation appearing near the gas entrance of the expansion region with a tapering angle increases. This causes velocity peaking near the reactor symmetry plane and complicated transport of gas-phase species along the streamlines of the return-flow. If an optimum gas flow rate which gives minimum return-flow and uniform macroscopic spatial distribution for flow pattern and gas-phase species can be determined, then it is desirable to change the gas flow velocity and the gas pressure on the condition that the gas flow rate is maintained.

Effect of Evaporation of Liquid Droplets on the Distribution of Parameters in a Two–Species Laminar Flow

Abstract: A calculation model was developed, and the heat– and mass–transfer characteristics in a laminar air—vapor—droplet flow moving in a round tube were studied numerically The distributions of parameters of the two–phase flow over the tube radius were obtained for varied initial concentrations of the gas phase The calculated heat and mass transfer is compared to experimental data and calculations of other authors It is shown that evaporation of droplets in a vapor—gas flow leads to a more intense heat release as compared to a one–species vapor—droplet flow and one–phase vapor flow

Energy Transfer Analysis of Turbulent Plane Couette Flow

Abstract: An energy transfer analysis of turbulent plane Couette flow is performed It is found that nonlinear interaction between the [0, ±1] modes is principally responsible for maintaining the mean streamwise turbulent velocity profile The [0, ±1] modes extract energy from the laminar flow by linear non-modal growth mechanisms and transfer it directly to the mean flow mode The connection of this work to linear/nonlinear models of transition is discussed

A flat plate solar collector with dual channels for air flows

Abstract: An analysis was made on the thermal performance of a flat-plate solar collector in which the air flows both in upper and under channels of the absorber plate. The results were compared with experimental results. The analytical results agreed well with the experimental results in the case that the ratio of the flow rate of the upper channel to the total flow rate, /spl beta//sub 2/, was in the range between 0 and 0.5. It was found that generally the flow in the upper channel increased the thermal efficiency. For example, the increase in thermal efficiency for turbulent flow was 14% at /spl beta//sub 2/=0.2 when the inlet air temperature was the same as the ambient air temperature. For laminar flow, larger increase of the efficiency, as much as 30%, was obtained. The effect of the total now rate and /spl beta//sub 2/ on the collector efficiency and temperature rise of the flow in each channel was also discussed.

Improving the flow of stirred vessels with anchor type impellers

Abstract: Anchor impellers have a simple and basic configuration which is well suited for the mixing of highly viscous flow, normally in the range of viscosity from 10–100 Pa.s, typical of polymer reactions. It is widely used in chemical and food industries. The primary flow generated by this radial impeller has been reported much more than the secondary flow in the literature. The great majority of these investigations refers to experimental works. The experimental works, however, have not been able to give a detailed picture of the flow, specially for the secondary flow. This is particularly important, because the secondary flow controls heat transfer in stirred tanks under laminar flow. Some computational investigations have been reported but the meshes shown are normally very coarse and some simplifications such as flat bottom are assumed for the models. The main contribution of this paper is to present a detailed picture of the secondary flow generated by anchor impellers both for Newtonian and pseudo-plastic fluids. The case study of orange juice mixing is analyzed.

Laminar flow of fine sediment-water mixtures

Abstract: Flows of sediment-water mixture (suspensions) are common superficial processes in nature. To investigate the possibility of predicting the behaviour of such flows, we study the free surface flow of a clay-water suspension down a slope, which may represent a simple realistic model for the flow of some concentrated sediment-water mixture in a natural environment. The hydrodynamic lubrication equations governing the flow are derived from the full Navier-Stokes equations, including an appropriate tensorial expression for the constitutive equation of the suspension (a Herschel-Bulkley fluid with a hysteresis in the yield strength). Results have been obtained for the free surface and length of an unsteady, laminar, isothermal flow of the suspension. The theory is in good agreement with laboratory experiments with fine clay suspensions.

Gas injection from the surface of a triangular plate in a hypersonic flow

Abstract: The flow formed as a result of gas injection through the permeable surface of a triangular plate is investigated in the regime of strong viscous-inviscid interaction between the hypersonic flow and the laminar boundary layer. The features of the flow past strongly cooled surfaces with the formation of supercritical and subcritical flow regions in the boundary layer are studied. The injected gas distribution ensuring the existence of self-similar solutions in the supercritical flow regions is obtained.

Indications of Segmental Flow in Straight Pipes by Flow Injection with Spectrophotometric Detection

Abstract: A procedure of spectrophotometric analysis of fluid flow in pipes is described and its performance is tested on three different dye compounds. The procedure follows measurement and mathematical de-convolution of the signal with an exponential function that is associated with molecular diffusion. Evidence is provided for the presence of segmental flow and the three dye compounds, used as tracer molecules, indicate that the solute molecules gain velocity, predominantly in the streamwise direction, from the solvent flow rate. The additional velocity, as gained from the solvent flow rate, depends on a kinetic-diffusion constant and the internal friction of the system. The model allows a calculation of the flow-injection signal and serves as a tool for the investigation of properties of fluid dynamics.

Visualization and Quantification of Laminar Flow Mixing in a Stirred Tank Reactor

Abstract: Laminar flow mixing in a stirred tank reactor is simulated by tracing a large number of particles. The stirred tank has a flat blade disc impeller with 4 blades and no baffles. The flow fields are solved using Fluent, a commercial CFD software package. The impeller Reynolds number is less than 50 and the flow is assumed to be steady in a rotating frame fixed on the impeller. A code is developed to trace fluid particles in the flow field, visualize 3D mixing processes in the tank, and quantitatively analyze the mixing status. The animated mixing processes reveal that fluid elements are repeatedly stretched and folded, a typical process in chaotic mixing, by the blades when they pass near the tips. Mixing is quantified by measuring volume percentage of the tank covered by the particles and the variance of particle spatial distribution. Both visualization and quantification results show that mixing in this stirred tank is poor for all the impeller speeds studied.

Deposit Growth on Chemical Reactor Walls and the Associated Heat and Mass Transfer

Abstract: A mathematical model is formulated for the crystallization of the product of a bimolecular reaction in a laminar flow of a viscous solution containing foreign solid particles that serve as crystallization centers. A model is reported for the layerwise formation of a deposit consisting of the reaction product crystals and the foreign solid particles on the walls of a continuous flow reactor. A classification of the deposits is suggested, and the formation rate of the deposits of some types is calculated in the framework of the formulated model. The role of the reactor design in deposit formation is disclosed. The hydrodynamic interaction between the crystals formed in a reactor and those deposited on its walls is studied.

Effect of fluid viscoelasticity on the law of pulsating laminar flowing in pipeline

Abstract: The law of pulsating laminar flow under the pushing of periodic pressure gradient is obtained by the combination of Maxwell fluids'constitutive equation and momentum equation of laminar flowing in the round pipe. The law of velocity distribution under different frequency and relaxation time is presented. The Maxwell fluids flowing law in the period from 0 to 2π and the factors affecting the velocity distributions of Maxwell fluids, such as the relaxation time and frequency, are analyzed. The result of numerical computation shows that the velocity amplitude is reduced with the increases of the frequency and the relaxation time.

Time-dependent simulations of laminar and turbulent flows in COIL geometries

Abstract: : In this work, we report CFD studies of possible unsteadiness (flow transition and turbulence) effects in the injector/nozzle geometry of the Phillips Laboratory RotoCOlL (Chemical Oxygen Iodine Laser) Device. Earlier numerical studies based on the MINT code assumed steady, laminar device flow as necessary compromise for the complicated reacting flow COIL problem. Other studies based on the GASP code involve similar assumptions. Also, other studies to date assume the so-called unit cell' approximation. The unit cell approximation is the assumption that the flow in the COIL geometry is periodic with period equal to the distance between small (downstream-located) iodicne injectors and half the period between the large (upstream-located) I injectors. Our work examines the validity of this assumption and estimates its effect on the flow. Relaxation of the unit cell will be, we believe, important in future work.

Laminar counterflow of two mutually insoluble liquids within a narrow slot

Abstract: Laminar counterflow of mutually insoluble liquids in a narrow slot is discussed. Expressions relating the velocity profiles in upward and downward flows with the physical properties of the liquids and volumetric flow rates are suggested. An equation for the volumetric flow is proposed for the case of inversionless movement (zero flow rate at the interface).