Showing papers on "Laminar flow reactor published in 1989"

Pipe flow measurements of a transparent non-Newtonian slurry

Abstract: An experimental description of the flow structure of non-newtonian slurries in the laminar, transitional, and full turbulent pipe flow regimes is the primary objective of this research. Experiments were conducted in a large-scale pipe slurry flow facility with an inside pipe diameter of 51 mm. The transparent slurry formulated for these experiments exhibited a yield-power-law behavior from cup viscometer measurements. The velocity profile for laminar flow from laser Doppler velocimeter (LDV) measurements had a central plug flow region, and it was in agreement with theory. The range of the transition region was narrower than that for a Newtonian fluid. The mean velocity profile for turbulent flow was close to a 1/7 power-law velocity profile. The rms longitudinal velocity profile was also similar to a classical turbulent pipe flow experiment for a Newtonian fluid; however, the rms tangential velocity profile was significantly different.

Scaling up of a monolithic catalyst reactor with two-phase flow

Abstract: Scaling up of the monolithic three-phase reactor has been studied in the hydrogenation step of anthraquinones for large-scale production of hydrogen peroxide. The influence of flow pattern (bubble flow and slug flow), flow distribution, pressure drop, and mass transfer has been investigated. It is illustrated that the segmented gas-liquid flow (slug flow) gives the highest production rate with very small scale-up effects.

On the products of the heterogeneous oxidation reaction at the surfaces of burning coal char particles

Abstract: The combustion of the char particles of two bituminous coals were investigated in a laminar flow reactor having gaseous environments containing 6 and 12 mole-% oxygen in the temperature range 1550 to 1700 K. Measurements of the size, temperature and velocity of individual particles were made at selected heights above the reactor inlet and hence, at different extents of burnoff. Samples of partially reacted chars, extracted from the reactor at these same heights, were analyzed in order to determine the fraction of the initial mass remaining, m/m o , and the char density. The data were used in the governing mass, momentum and energy balance equations in order to determine overall particle burning rates per unit external surface area. The burning rates determined indicate that account must be made of CO 2 formation in the vicinity of the particle. Whether the CO 2 is formed heterogeneously at the particle surface, or homogeneously in the particle's boundary layer cannot be established definitively. It is shown, however, that the single-film model of a burning carbon sphere with a fraction ψ of the carbon being converted to CO 2 at the particle, surface adequately describes the burning behavior of coal char particles in the 75 to 125 μm size-range. Employing such a model, for the char particles of the bituminous coals investigated, as much as 15% of the carbon content of the particle can be converted to CO 2 at temperatures in the range 1600 to 1700 K. At temperatures above 1800 K. CO is essentially the sole heterogeneous reaction product.

The Laminar Flow in the Developing Region of a Rotating Pipe

Abstract: In this paper, velocity profiles of the laminar flow in the developing region of an axially rotating pipe are analyzed numerically and are compared with the experimental results when an uniform axial flow is introduced into it. It is found that the axial velocity in the rotating pipe exceeds the value of the Poiseuille flow at the center, and a backward flow appears near the wall as the swirl ratio becomes large. The greater the swirl ratio N becomes, the more remarkable it tends to become ; but at about N = 3 experiments show that the rotation of the pipe causes the flow to become unstable and the development of the flow is delayed.

The identification of two distinct laminar to turbulent transition modes in pipe flows accelerated from rest

Abstract: A study was undertaken to investigate transition in a pipe flow accelerated from rest. Experiments were carried out on a vertical tube under a constant head of liquid: flow was initiated by opening a solenoid valve. A wall shear stress probe used in the role of an event recorder identified two transition events, separated by the passage of a turbulent to laminar front and a period of laminar flow. Evidence suggests that the first comprises a laminar to turbulent interface arising from a ‘natural’ stable/unstable front moving up the tube as local conditions become met, while the second is consequent upon the formation of a continuous turbulent structure carried down the tube from the inlet by the bulk flow. The paper provides a formal explanation of a phenomenon which is typical of that which is observed in starting pipe flows with a disturbed inlet.

Particle rotation in coal combustion: statistical, experimental and theoretical studies

Abstract: Fast particle rotation (up to 3,000 cycles/sec) was observed and recorded by high-speed cinematography and fiber optic radiometry during the combustion in a laminar flow reactor of coal particles and coal-water fuel (CWF) agglomerates. A theoretical model of particle rotation developed to predict the angular velocity of rotating coal particles or CWF agglomerates during devolatilization and char burnout is based on volatile ejection from pores, assumed to be randomly oriented. The angular velocity of the rotating particle is shown to be domainated by the volatiles ejected from a small number of macropores and dependent upon the particle heating rate and particle size. Because of the random pore distribution, a range of geometrical factors for the devolatilization pores is predicted by the model, in general agreement with the statistical results on the rotation frequency distribution observed experimentally.

Buoyant laminar flow of air in a long, square-section cavity aligned with the ambient temperature gradient

Abstract: Numerical solutions have been obtained for three-dimensional buoyant flow of air under laminar conditions in a slender, square-section cavity lying parallel to the gradient vector of the temperature field in which it is embedded. Velocity and temperature profiles in the cavity are presented in support of a flow model in which primary and secondary circulation are reconciled by an advective mechanism in the central region. The effect of the temperature gradient, represented by a Rayleigh number, is explored when the cavity is horizontal. The effect of inclining the cavity above and below this horizontal position is also explored. Comparisons are made with related work on cylindrical and two-dimensional rectangular cavities.

Effects of heat release on the structure and stability of a coflowing, chemically reacting jet

Abstract: It is shown how linear stability analysis and full simulations can be used to study the stability and structure of reacting flows. The small effect of gravity on steady laminar flame heights can be modeled if allowance is made for the density variations due to heat release. It is found that cold transitional jet simulations yield perturbation growth rates which are consistent with the predictions of the inviscid stability theory.

Recirculating mixed convection flows in rectangular cavities

Abstract: A numerical investigation is carried out to determine the flow and thermal structures of mixed convective flow in a rectangular cavity. The effect of aiding and opposing buoyancy on the flow in a vertical downward laminar jet is studied for Re < 200, -1.0 < 'Ri < 0.5, and 0.5 < A < 5.0. Such flow situations occur in enclosure fires, energy storage, and ventilation systems. Results of the velocity profile, temperature distribution, local friction factor, and heat-transfer coefficient are presented for both hot and cold jets. The flow configuration is found to be strongly affected by the positive and negative buoyancy and also by the aspect ratio of the cavity.

Axial reactor with coaxial oil injection

Abstract: An axial flow carbon black reactor (10) for producing carbon black particles having a relatively narrow particle size distribution. Feedstock oil is introduced into the reactor by a spray nozzle (12) located coaxial with the longitudinal center line of the reactor. The oil spray flows either in the countercurrent or the concurrent direction relative to the flow of hot gas through the reactor and produces an oil spray pattern covering either substantially the entire frontal area of the hot gas flow or substantially less than the frontal area. Countercurrent feedstock flow from (23) increases coverage of the gas flow area by the oil spray and narrows the particle size distribution of carbon black produced by the reactor, and concurrent feedstock flow produces the opposite result.

Peak simulation for non-segmented continuous flow systems

Abstract: Understanding of the dispersion of a solute injected as a sample plug into a laminar flow system through a small-bore tube with a circular cross section is important in the design of flow analysis apparatus and systems such as flow injection analysis and various chromatographic technologies. We have solved the diffusion-convection equation by a finite element method. The convection and diffusion behavior of the solute were computed, and the concentration distributions in the tube were analyzed by a concentration map and peak response profile

Dispersion behavior of solutes in an ideal laminar flow with small-bore glass tubes.

Abstract: The dispersion behavior of solute molecules injected as a sample plug into an ideal laminar capillary flow was experimentally analyzed by means of microscopic and microphotometric methods. The flow pattern in small-bore glass tubes was directly observed by the microscopic method using a camera. The peak responses obtained for the colored solutes by means of the microphotometric method consist of double-humped peak features which resulted from both laminar flow convection and the molecular diffusion of solute molecules at the parabolic interface between the sample plug and the carrier fluid. The influences of the diffusion coefficient of the solute, the flow rate, the tube length, the tube diameter, etc. were mainly investigated in order to guide the design and optimization of the flow systems of capillary liquid chromatography (CLC), capillary electrophoresis (CEP), flow-injection analysis (FIA), etc. The experimental results obtained here are in good agreement with the theoretical results obtained by the...

Laminar and turbulent flow continuous interfacial polycondensations of nylon 66

Abstract: The interfacial polycondensations of nylon 66 in a continuous reaction system have been studied. An experimental stirred flow reactor was used to determine both yield and intrinsic viscosity (molecular weight) as functions of reactant ratio (adipoyl chloride/hexamethylene-diamine), and Reynolds number from laminar to turbulent flow. It was found that mass transfer was the controlling factor in the reaction system. The yield as a function of Reynolds number was found to directly correlate with the behavior of the combination of mass transfer coefficient and interfacial area. Intrinsic viscosity had maximum values in the same reactant ratio range as for batch and continuous cascade systems studied earlier. Intrinsic viscosity behavior was shown to relate to interfacial area behavior.

Countercurrent gas absorption with chemical reaction in a laminar falling film

Abstract: An analytical solution for absorption of a gas with an accompanying first order reaction in a laminar falling film is developed. The gas flow is countercurrent to that of the liquid film. Change in the gas phase concentration because of the reaction, as it happens in practical situations, has been taken into account. Some computed results are presented to show the effects of the system parameters—namely, the reaction rate parameter, the Biot number, and the absorption factor— on the mass transfer enhancement factor and on the fractional removal of the feed gas over a given non-dimensional film length.

Laminar radial flow electrochemical reactors. III. Electroorganic sysnthesis

Abstract: This paper investigates the performance and design of three laminar radial flow electrochemical cells (the capillary gap cell, stationary discs; the rotating electrolyzer, co-rotational discs; the pump cell, one disc rotating and the other stationary). Modeling of a competing electrosynthesis pathway is described — the methoxylation of furan. The model developed incorporates convective, diffusive and migrative influences with three homogeneous and two electrodic reactions. Two sizes of reactors are considered and the performance of the different reactor types analyzed as a function of size. The superiority of the rotational cells is illustrated for this reaction scheme compared to both the capillary gap cell (CG) and a parallel plate reactor (PPER). Scale-up criteria are scrutinized and two approaches to laminar radial flow reactor scale-up are investigated. The one suggested herein shows that Taylor number, residence time,IR drop and rotational Reynolds number must all be accounted for even with a fairly simple electrosynthesis pathway. A quantitative evaluation of this scale-up procedure is included.

Subsonic pressure recovery in cylindrical condensers

Abstract: A method is presented for predicting laminar, subsonic flow in axisymmetric cylindrical heat pipe condensers. The method involves the use of the boundary layer approximation and a noncontinuous power series to describe the velocity profile under conditions including strong axial flow reversal. A comparison between laminar predictions and measurements indicates that transition to turbulent flow in the condenser begins when the absolute value of the radial Reynolds number exceeds 6. The condenser pressure recovery in the turbulent regime can be calculated from the momentum flow at the condenser inlet and an empirical wall-friction parameter.

A Study of Controlling Generation of a Benard Cell in the Laminar Combined Convection in a Horizontal Rectangular Duct Heated from Below

Abstract: Thermal CVD reactors of a horizontal rectangular duct are widely used in the production of semiconductor layers, but in the process strong vortexes having axes in the flow direction prevent uniform growth of the layer. This research aims at a fundamental study of controlling strong to provide horizontally uniform fluid temperature. Experiments reveal three typical flow patterns caused by heating the side walls. Those are: a flow of a single-pair Benard cell, and unsteady flow with time-averaged uniform temperature and a pair of vortexes with circulation opposite to that of a Benard cell. Numerical calculations assuming a laminar, steady 2-dimensional flow were made by a SOR method. Experimental and predicted results were compared and indicated agreement in strong vortex cases, but little agreement otherwise.

鉛直面上の体積力対流凝縮 : 第2報,凝縮液膜の流動と平均熱伝達係数

Abstract: This paper deals with the studies on body forced convection film condensation of pure and single-component vapor on a vertical smooth surface. The flow patterns of condensate film on a vertical smooth surface are classified into ten kinds of flow: L flow (laminar flow), S flow (sine wavy flow), H flow (harmonic wavy flow), T flow (turburlent flow), L-S flow, L-S-H flow, L-S-H-T flow, S-H flow, S-H-T flow and H-T flow, Nondimensional expressions of the mean heat transfer coefficient are obtained form the ten kinds of condensate film flow and compared with the experimental results, respectively.

Intestinal Absorption Kinetics Using a Laminar Flow Model

Abstract: The drug concentration profile at non-steady state in the intestine was simulated using a laminar flow model. The transport equation with cylindrical coordinates was solved by a finite difference method to stimulate the concentration profile in the tube and the exit cup-mixing concentration. A drug with a various wall permeability coefficient (Pw = zero or 10(-5) to 10(-3) cm/s) and diffusion constant (D = 10(-6) to 10(-4) cm2/s) was assumed to be introduced into the tube in a pulse form. The spatial intervals of the grid and the time step were varied to yield the optimum condition for calculation. The concentration profile in the tube as the time elapsing and the exit cup-mixing concentration versus time profile were shown graphically. Pw and D influenced the concentration profiles. This suggests the possibility of the estimation of Pw and D by determining the exit cup-mixing concentration after a pulse input to a perfused intestine under a laminar flow condition.

Conjugate heat transfer in the laminar flow of a swirled incompressible fluid in a horizontal annular duct

Abstract: The heat transfer associated with swirled flow of a heat-transfer medium in a semi-infinite annular duct is analyzed numerically. The walls of the duct have a finite thickness and exert a significant influence on the formation of the temperature fields in the fluid.

Flow in the initial segment of a tube with a sharp inlet edge. Comparative analysis

Abstract: When flow becomes detached in the inlet segments of tubes and channels with sharp leading edges and where the Reynolds numbers exceed 75·103, the displacement of the maximum of the local heat transfer is in agreement with the onset of secondary laminar flow.

Calculating the nonsteady exchange of mass and heat in the laminar flow of dissociating nitrogen tetraoxide in a fuel-cell cluster

Abstract: We propose a method for the numerical calculation of the nonsteady exchange of mass and heat in the flow of a chemically reactive coolant in channels of complex shape. As an example we present the results from the calculations of heat and mass exchange in the laminar flow of dissociating N2O4 for a triangular fuel-cell cluster.