Mass transfer at low flow rates in a packed column

Abstract

Mass transfer in packed columns has been investigated for a variety of column and packing sizes but at flow rates restricted to fully developed turbulent conditions. The present work was undertaken to investigate mass transfer at flow-rate conditions in the transition and laminar regions.A dual treatment of experimental data required a knowledge of the variation of concentration and velocity with radial position. A tracer-injection technique was employed which consisted in the introduction of a tracer gas into the center of a bulk gas stream and the measurement of the tracer-gas concentration at various radial positions downstream. The velocity distribution for the packed column was determined by means of a five-loop, circular, hot-wire anemometer. The test column was a vertical 4-in. pipe, packed with &in. spherical, ceramic catalyst-support pellets.Mass transfer diffusivity and Peclet number were determined from two solutions of the diff erential-diffusion equation applied in previous investigations. An analytical solution in terms of Bessel functions was used to calculate values of average diffusivity and Peclet number and a seminumerical solution in terms of homogeneous linear-difference equations to calculate values of point diffusivity and Peclet number.Variation of diffusivity and Peclet number with radial position is shown, average diffusivity and Peclet number being correlated with Reynolds number. The interaction of molecular and eddy mass transfer mechanisms with decreasing mass velocity is illustrated by defining a molecular and an eddy Peclet number and correlating with Reynolds number.Eddy difiusivity is correlated as a function of local flow conditions. *Tables 2, 3 and 4 are on file with the American Documentation Institute, Auxiliary Publicatione Photoduplication Service Library of Congress. Washington 25, D. C., and may be ordered a8 document No. 5871 on remission of $1.25 for microfilm or $1.25 for photoprints.

Preliminary Ion Exchange Modeling for Removal of Technetium from Hanford Waste Using SuperLig 639 Resin

“…As illustrated in Figure 8-1 velocity ratios greater than 100% can occur for columnto-particle diameter ratios less than 10 and beyond ~50 the impact is negligible. Also shown in Dorweiler and Fahien (1959) performed similar experiments that agreed with Schwartz and Smith (1953) and went to flowrates as low as 30 cm/min. In a later study by Fahien and Smith (1955) significant radial effects were observed for column-to-particle diameters less than 20.…”

Diffusion Behaviors of He and CH4 in Air Flow through Packed Bed

“…10,11) The basic differential equation for mass transfer, which considers diffusion in the radial direction only and bulk flow in the axial direction, is written as Eq. (1) 6.…”

Pore‐scale simulations of unsteady flow and heat transfer in tubular fixed beds

“…A way to improve the pseudo‐homogeneous approach is to take into account the effect of the radial distribution of packing porosity on the overall heat‐transfer properties. Several hydrodynamic investigations were carried out 30 or 40 years ago by laser velocimetry or by hot‐wire anemometry,57–59 but the measurements were made at the outlet of the packing. The velocity profile depends greatly on the clearance, and the radial fluctuation of the velocity was smoothed and showed only one peak close to the wall.…”