Diffusion in packed beds at low flow rates

Diffusion rates were measured in a 2-inch I.D. column, packed with 1/3- to 1/2-inch spherical particles and through which nitrogen flowed. Carbon dioxide was introduced into the center of the bed and its concentration measured 4.75 inches downstream. Measurements were made in the low range of modified Reynolds numbers, from 3 to 80, where data are scarce. Modified Pedet numbers were computed from the data by using a finite-source solution to the equation expressing the concentration as a function of position. For the range of conditions studied the simpler point source solution would give results about 10% low. The importance of axial diffusion was analyzed by computing the effect of the magnitude of the axial diffusivity on the radial diffusivity. For the low Reynolds numbers employed in the present study the final results were obtained by assuming that the axial and radial diffusivities were equal.