Gas flow and heat transfer through catalyst filled tubes

A detailed knowledge of the fluid flow profile and of the radial heat transfer parameters is essential for a proper design of fixed-bed processes. For different sphere, ring and cylinder catalysts radial velocity profiles were measured below the fixed-bed at empty tube velocities of air between 0.5 m.s(-1) < (0) < 1.5 m.s(-1) and tube to particle diameter ratios 3.3 < d(t)/d(p) < 11. As a consequence of the statistical behaviour of packings, it was necessary to average velocity measurements after repacking in order to obtain representative flow profiles. All profiles show a velocity maximum in the vicinity of the wall, in order to relate the measured profiles below the packing to the velocity profiles inside the packing, model simulations have been performed. The model is based on the extended Brinkman equation and the independently determined radial void fraction profiles. It considers an effective viscosity for which correlations have been derived for spheres, cylinders and rings. Radial heat transfer parameters were obtained experimentally from packings between two parallel plates of different temperatures. The determined heat transfer parameters can be transformed to the round cross section of a tube by considering the respective radial velocity profiles. The transformed values of the effective heat conductivity could be well described by literature correlations. For the heat transfer coefficient at the wall a new correlation was developed. (C) 2001 Editions scientifiques et medicales Elsevier SAS.