Year: 2009
Type: dissertation
Abstract: ENGLISH ABSTRACT: Packed beds are widely used in industry to improve the total contact area between two substances in a multiphase process. The process typically involves forced convection of liquid or gas through either structured or dumped solid packings. Applications of such multiphase processes include mass transfer to catalyst particles forming the packed bed and the adsorption of gases or liquids on the solid packing. An experimental study on the determination of air flow pressure drops over different packingmaterialswas carried out at the Telemark University College in Porsgrunn,Norway. The packed bed consisted of a cylindrical column of diameter 0.072m and height 1.5m, filled with different packingmaterials. Air was pumped vertically upwards through a porous distributor to allow for a uniform inlet pressure. Resulting pressure values were measured at regular height intervals within the bed. Due to the geometric nature of a Raschig ring packing wall effects, namely the combined effects of extra wall shear stress due to the column surface and channelling due to packing adjacent to a solid column surface, were assumed to be negligible. Several mathematical drag models exist for packed beds of granular particles and an important question arises as to whether they can be generalized in a scientific manner to enhance the accuracy of predicting the drag for different kinds of packing materials. Problems with the frequently used Ergun equation, which is based on a tubular model for flow between granules and then being empirically adjusted, will be discussed. Some theoretical models that improve on the Ergun equation and their correlation with experimental work will be discussed. It is shown that a particular pore-scale model, that allows for different geometries and porosities, is superior to the Ergun equation in its predictions. Also important in the advanced models is the fact that it could take into account anomalies such as dead zones where no fluid transport is present and surfaces that do neither contribute to shear stress nor to interstitial form drag. The overall conclusion is that proper modelling of the dynamical situation present in the packing can provide drag models that can be used with confidence in a variety of packed bed applications.
Author: Christo Rautenbach
Language: English
Subfield: Computational Mechanics
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W395611166