Radial Peclet Number Research Articles

Mixing of chemically reactive fluids by swirling in a tubular reactor

To achieve a varying degree of radial mixing in a single phase fluid, a stable laminar swirl is created by two fluid streams tangentially entering a tubular reactor. The details of the resultant fluid motion is described using the material stretching coordinate technique. The combination of fluid motion, molecular diffusion, and intrinsic chemical kinetics provides the basis for investigating mixing with chemical reactions for nonpremixed feeds. Computations on an infinitely fast second-order reaction for the radial Peclet number ranging from 10 2 to 10 6 reveal the following features for

The Oxidation of Ethene in an Empty and Packed Tubular Wall Reactor Operating in the Reaction- and Diffusion-Controlled Regimes

The behaviour of the empty and packed isothermal tubular active wall reactor operating under diffusion- or reaction-limited conditions has been analyzed both theoretically and experimentally. By various numerical procedures the mass transport equations have been solved for the case of a first-order reaction taking place at the tube wall, either laminar or plug flow prevailing in the reactor. Using the platinum-catalyzed air oxidation of small concentrations of ethene, it has been found that in the laminar-turbulent transition region as well as in the laminar flow region the theoretically calculated and experimentally measured profiles agree well. Although, also for the packed tubular wall reactor, the calculated and measured mass transfer coefficients are in excellent agreement when assuming a radial Peclet number of 7.5, the values are lower than those reported recently in the literature.

Effective wall heat transfer coefficients and thermal resistances in mathematical models of packed beds

AbstractExpressions are derived for an effective wall heat transfer coefficient useful in one‐dimensional representations of heat transport in packed beds. These expressions are obtained with two mathematical models of a cylindrical packed bed: a partial differential model and a finite stage model. These expressions relate the effective wall heat transfer coefficient, which is a local coefficient, to the actual wall heat transfer coefficient and the bed diameter (and the radial Peclet number in the partial differential model) in regions of the bed where similar temperature profiles obtain. These relations involve a single dominant root of an equation characteristic of the heat balance equations of each model.From these relations, expressions for an effetive thermal resistance of the bed are obtained. For each model, this bed resistance is found to be an approximately linear function of the bed diameter and to be rather insensitive to the actual wall heat transfer coefficient. For each model, an approximate bed resistance is found that is not dependent upon the actual wall heat transfer coeficient and with which the effective wall heat transfer coefficient can be estiamted with an error of less than 7%.

Some remarks on longitudinal mixing or diffusion in fixed beds

AbstractIt has been shown both theoretically and experimentally that the radial Peclet number in a packed bed approaches about 11. If it is assumed that the interstitial volume of the bed forms mixing cells, then a comparison of the solutions obtained from the mixing and turbulent diffusive mechanisms shows that the axial Peclet number for agreement of the two must be about 2, as a limiting case for high Reynolds numbers. This is substantiated by experiment.