Although considerable work has been done on the problem of heat transfer radially in fixed beds through which gases are flowing, the data available for mass transfer are limited to one pipe size and one packing size and refer to average diffusivities for the entire bed. The present study was undertaken to determine: (1) diifusivities over a range of pipe and packing sizes and (2) the effect of radial position in the bed. Empirical correlations are then presented for both point Peclet numbers, which vary wit11 radial position, and average Pedet numbers for the entire bed.The variations in Peclet number with radius can be explained in terms of the corresponding variation in void fraction for 81% of the radius of the bed. A t modified Reynolds numbers above 40 to 100 the equation Pe = 8.0 + 100 ( 6 -6,) correlates the effects of pipe and packing size and radial position. At radial positions greater than 0.81 wall friction influences turbulence conditions and the Peclet number.

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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.

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