Equivalent Diameter of Packed Solids in Mass Transfer between Solids and Fluid

Abstract

In solid catalytic reactions and diffusion operations, a packed bed of cylindrical or ring-type solids as well as spherical solids is often employed, and these shaped solids have a distribution of diameter of length. However, no correlation expression for average mass transfer coefficient (k_f) in such cases has been published.
In the present work, the mass transfer rates of shaped benzoic acid (cylinders of equal or different diameter and length, spheres of different diameter, rings of equal diameter and length, and mixtures of spheres and cylinders) were measured by the dissolution into flowing water in the Reynolds number (Re) range of 1 to 120, and the Schmidt number (Sc) range of 346 (50°C) to 777 (30°C).
As a result, the equivalent diameter (d_ps) based on the sphere of equal surface area was adopted as the representative dimension of packed solid, and the following equation for spherical solid of equal diameter was applied exactly for the above solid-fluid systems.
J_D'= (k_f/u) Sc^1/2= 0.70Re^-0.61, 1 < Re = d_psuρ / μ<120