Axial Concentration Distribution Research Articles

円すい型容器内二成分粒子偏析過程における軸方向濃度分布

In order to investigate the axial segregation profile of binary solid mixtures during the mixing and segregation processes in a horizontal rotating conical vessel, experiments were carried out by using several kinds of binary mixtures, such as alumina/silica sand mixture and different size silica sand mixtures, as materials. The axial concentration distribution of the mixtures was measured at a different mixing time under three different initial loading conditions at the rotating speed of the vessel n=10-30rpm.It was confirmed that the demixing potential φ, proposed in the Rose's Equation, was correlated with the concentration CA of the specified particles within a specified zone of the vessel, which was itself closely related to the axial arrangement of the particles in the vessel, regardless of the mixture or dimension of the vessel. With the aid of this relationship between φ and CA, it was possible to estimate the axial concentration distribution of a mixture in the vessel.

Separative Performance Transients in a Gas Centrifuge

A general method has been developed to calculate the behavior of the exit compositions from a gas centrifuge under unsteady conditions. The method utilizes the basic enrichment gradient equations derived by Cohen, which, in this case, contain time derivatives of the partial /sup 235/U inventories. These partial differential equations are converted to ordinary differential equations by a linear approximation to the axial concentration distribution for use in the inventory terms only. With this simplification, analytical solution is possible for the feed concentration transient. The transient driven by a change in the feed flow rate, however, requires numerical solution. For analysis of ideal cascades in the unsteady state, the transient flow and separation characteristics of the centrifuge must be combined with total uranium and /sup 235/U material balances on each stage.

Fortschritte bei der Modellierung von Festbettreaktoren

AbstractProgress in the modeling of fixed bed reactors. Recent work on the modeling of catalytic fixed bed reactors have led to more realistic mathematical models and to a better understanding of problems connected with modeling. Nowadays standard routine computer programs are available for use in the design (and analysis) of catalytic fixed bed reactors for very complex reaction systems. The influence of bed structure on transport parameters was illustrated by experimental determination of axial and radial concentration and temperature distribution. Moreover the problem of multicomponent diffusion coupled with complex reactions in porous catalysts has been solved and can be included in the reactor model. However, the practical application of possible reactor models is limited by the availability of transport parameters for fixed beds.

Dispersion models of unsteady tubular reactors

AbstractAxial dispersion in time‐variable laminar flow in a tubular reactor is analyzed using an exact procedure for the case of a homogenous first‐order reaction. For the first time since the Taylor Dispersion model was originally introduced for the modeling of reactors, its validity is examined over a wide range of the reaction rate parameter by comparison against an exact analysis. It is shown that a constant coefficient dispersion model can be obtained from first principles for large values of time only for initial distribution problems; however, this simple approximate model also is reasonably good for describing concentration distributions for the present inlet distribution problem for slow reactions and for axial locations sufficiently far away from the inlet. For rapid reactions, while the dispersion model is inaccurate in describing axial concentration distributions, it is surprisingly good for predicting the reactor length required for complete conversion. In contrast to the conclusion of a recent article, it will be shown that the dispersion coefficient is independent of the reaction rate constant.

Two‐Dimensional Current Distribution Within a Packed‐Bed Electrochemical Flow Reactor

An analysis is presented for describing behavior of a packed‐bed electrode confined within a thin cylindrical porous separator and surrounded by a concentric counterelectrode. Electrolytic solution, containing reactive species, flows axially in plug flow through the packed‐bed electrode while the peripheral surface of the packed bed is held under a constant applied potential. Results are obtained for two types of porous separators, (i) permeable to all solute species and (ii) impermeable to the reactive solute species. For each case, the two‐dimensional (radial and axial) concentration, potential, and current distributions are calculated by a finite difference method. The results clarify over‐all reactor performance and, in particular, predict the relation between the volumetric reaction rate and the residence time for a wide range of system parameters.

A method for the determination of additive elements in sintered tungsten metal rods by fast neutron activation analysis

A non-destructive activation analytical method developed for the determination of the axial concentration distributions of Al, Si and K residual additives in sintered tungsten rods is briefly described. A 14 MeV neutron generator is used to produce the reactions27Al(n, p)27Mg,28Si(n, p)28Al and39K(n, 2n)38K and the activities are compared with standards. A weighted least-squares fitting program is used for peak area determination of the scintillation spectra. A scheme of the irradiating and measuring arrangement with a pneumatic sample-transfer system is presented. The system is applicable to large-scale routine analysis and lends itself well to automation. The results of preliminary measurements with this arrangement are given.

Homogeneous reactions in turbulent pipe flows—tubular non-catalytic reactors

An analysis of turbulent reactive flows in tubular non-catalytic reactors is presented for various reaction orders and rate constants. A numerical technique using the explicit finite difference method is employed to obtain changes in the radial and axial concentration distributions. It is shown that lower order reactions cause a more rapid decrease in the axial concentrations. The effect of Reynolds and Schmidt numbers on the conversion levels is also discussed. Particular emphasis is placed upon analyzing the phenomena near the wall region.

Eddy diffusivity of mass measurements for air in circular duct

Continuous injection of a tracer gas (nitrous oxide) on the centreline of a circular duct has been used to measure the eddy diffusivity of mass for turbulent air flow. Using axial concentration distributions the limitations of the ‘point source’ solution have been revealed, and a modified evaluation procedure has been used. For the Reynolds number range tested, 1.3 × 10 4−1.3 × 10 5, the eddy diffusivity of mass in the central region of the tube was found to be: ε Ma ν = 25,27 Re · 10 −4 − 3,82 . Using eddy diffusivities of momentum from previous studies, the turbulent Schmidt number varied between 0.7 and 1.0.