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The effective medium approach to radial fixed bed dispersion models, in which radial dispersion of mass is superimposed on axial plug flow, is based on a constant effective dispersion coefficient, D T. For packed beds of a small tube-to-particle diameter ratio (N), the experimentally-observed decrease in this parameter near the tube wall is accounted for by a lumped resistance located at the tube wall, the wall mass transfer coefficient k m. This work presents validated computational fluid dynamics (CFD) simulations to obtain detailed radial velocity and concentration profiles for eight different computer-generated packed tubes of spheres in the range 5.04 ≤ N ≤ 9.3 and over a range of flow rates 87 ≤ Re ≤ 870 where Re is based on superficial velocity and the particle diameter d p. Initial runs with pure air gave axial velocity profiles v z (r) averaged over the length of the packing. Then, simulations with the tube wall coated with methane yielded radial concentration profiles. A model with only D T could not describe the radial concentration profiles. The two-parameter model with D T and k m agreed better with the bed-center concentration profiles, but not with the sharp decreases in concentration close to the tube wall. A three-parameter model based on classical two-layer mixing length theory, with a wall-function for the decrease in transverse radial convective transport in the near-wall region, showed greatly improved ability to reproduce the near-wall concentration profiles.

In this poster we describe a new computer-controlled, base-catalyzed transesterification experiment to produce biodiesel from vegetable oil that we have implemented in our unit operations laboratory. The main educational goal of the experiment is to measure the reaction kinetics at several temperatures and evaluate the activation energy of the reaction. Using a computer control panel to operate the process that is contained in a hood gives it the feel of a larger scale industrial process and minimizes some of the dangers from the hazardous and flammable materials involved. The new experiment provides experience with an industrially relevant, "green" technology and affords us a chance to reinforce safety concepts and provide experience with standard operating procedures and electronic batch records.