Packed beds find extensive application in a wide variety of industries to cany out a large number of diverse processes. The main objective of the present work is to develop models to predict the arrangement of particles and based on them, to determine and evaluate the structural characteristics of packed beds. These problems have received only a limited attention in the literature. As a first attempt, spheres of uniform size are considered. Beds of aspect ratio up to 2 (referred to as low aspect ratio beds) are analyzed by application of principles of analytical geometry. Expressions are derived for the location of particles and for the structural characteristics of the beds, both of which show periodicity. This leads to the concept of a unit cell which is the repetitive section of the bed whose characteristics are the same as those of the complete bed. The beds fall into three distinct groups — those with aspect ratio between 1 and l√3⁄2, between 1√3⁄2 and 2, and with aspect ratio 2. Equations are distinct for each group. The aspect ratio shows marked influence on the structural characteristics of the beds. Agreement of the predictions on the overall void fraction with the available experimental data is excellent. Radial void fraction profiles are estimated by defining a concentric cylindrical channel (CCC) of an arbitrary thickness and with the cylindrical surface through the radial position of interest located at the middle of the CCC, and by accounting for the solid volumes of all the segments (in this CCC) of spheres with centers lying within a distance of a particle radius on either side of the cylindrical surface. The curved boundaries of the sphere segments are rigorously accounted for. The results show that the entire bed is filled with variations in the void fraction, starting from a value of unity at the wall and zero (or close to zero) towards the axis of the bed. Monte Carlo model for the simulation of high aspect ratio beds has not proved successful even with any of a wide variety of distribution functions for the coordinates of the sphere dropping point. With uniform distribution, the only distribution used in all the reports so far, and with normal distribution, there is not even a qualitative agreement with the reported data on void fraction variations. Distributions with asymmetric density functions such as exponential, Weibull, gamma and beta, show considerable improvement; beta distribution being the best. However even the best results with beta distribution show satisfactory agreement with the experimental data only up to about 2dp from the wall. Simulations with the cluster growth model, modified to account for the confining nature of the wall, lead to more satisfactory results. The proposed algorithm consists of building up the cluster, sphere by sphere, by calculating all possible interior and wall sites for placing an incoming sphere in a stable and non-overlapping position on the current cluster. A preference parameter is defined to place the new sphere at locations along the cross section of the column at which the experimental void fraction profiles show prominent minima, that is, locations around which the bed has relatively high solid volume. Void fraction profiles in beds of various aspect ratios simulated by this model show good agreement with the corresponding experimental data. The structural characteristics of the high aspect ratio beds thus simulated are evaluated. The number of spheres per unit length, Ni is correlated with the aspect ratio. It becomes proportional to the square of the aspect ratio, with the proportionality constant being close to 0.9, for aspect ratios greater than about 10. This follows since in these beds the overall void fraction becomes constant at 0.4. Majority of the spheres have contacts (with neighboring spheres) between 4 and 7, with the lower and upper limits for the coordination number being 2 and 9. The radial profile of the average coordination number (averaged over the height of the bed at the given radial position) shows small oscillations about a mean value of about 6 over almost the entire bed cross section starting from a distance of about ldp from the wall. At a distance of 0.5dp from the wall the predominant number of contacts is four while the mean value is about 4.3. The overall coordination number (averaged over the entire bed) shows inverse dependence on the aspect ratio. For random packings, that is, as the aspect ratio becomes infinity, the overall coordination number tends to six which corresponds to regular cubic arrangement. Cumulative number fraction, CNf is a global measure of the arrangement of spheres in beds of high aspect ratio. Its radial variation shows four distinct regions whose locations are independent of the aspect ratio The CNf values in each region are correlated with aspect ratio The correlations combined with that of NL lead to a very useful and effective model for predicting void fraction profiles in a bed of any specified aspect ratio The validity of the predictive model is demonstrated

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Packed bed reactors are widely used in the chemicals industry and have been studied carefully in the last century. Several reaction engineering models have been developed in order to predict the behavior of such reactors under specified conditions, in order to assist in the sizing during an industrial process conception. These reactors can be categorized using different parameters, and the bed-to- particle diameter ratio - N - is one of them. It has been shown that this parameter influences greatly the transfer phenomena that occur in the bed, and that for ratios under 10, particular attention is needed when considering the wall effects. An impor- tant point that has to be evaluated is the accuracy of the actual chemical reaction engineering models when simulating such beds as it is valid to question the hypoth- esis of a pseudo-continuum model when considering a low bed-to-particle diameter ratio bed. Through high precision Computational Fluid Dynamics calculations, several beds of particles are modeled and studied in term of mass dispersion and reaction rate distribution. Two reaction engineering models - a simple pseudo-continuum model with effectiveness factor, and a model we refer to as "Single pellet" model - and several correlations regarding Peclet numbers are then evaluated under the same conditions in order to determine their accuracy and reliability for that particular kind of bed. Two beds of N = 5.96 and N = 7.99 are studied for dispersion phenomena, and the bed of N = 5.96 is studied for reaction rate distribution. It is shown that the pseudo- continuum model of dispersion stands valid for the higher N, but that none of the correlations we used were able to correctly predict the behavior of the N = 5.96 bed at any of the Reynolds number we considered, only giving close behaviors. We were confronted with some difficulties regarding the reaction simulation under Fluent, but some comparisons were successfully made regarding species and reaction rate distribution in the bed.

Thesis--Technische Universität München, 2008. / Includes bibliographical references.

Thesis (Ph.D)--University of Tulsa, 1995. / Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 1999. / Title from document title page. Document formatted into pages; contains xiii, 131 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 61-64).

Thesis (M.S.)--University of California, Berkeley, 1959. / "Chemistry-General" -t.p. Includes bibliographical references (p. 52-53).

Thesis (M.S.)--University of California, Berkeley, 1962. / "UC-38 Engineering and Equipment" -t.p. "TID-4500 (17th Ed.)" -t.p. Includes bibliographical references (p. 82-83).

High performance catalyst supports and packing materials are playing an increasing role in many reactions and separations. The dispersion in packed bed reactors and separation columns can be reduced by the development of new packing structures having open and connected pore geometries. The application of new materials in High Performance Liquid Chromatography (HPLC) with sub 5 micron particle sizes are growing. These small particles offer better performance and improved bed and column efficiencies. Recently developed, twinned Alumina Nanosheets (TAN) are 2D/3D nanomaterials that offer promising open geometries for use as column packings and catalysts supports. They have a small particle size (4 um in length, 1 um in width and 0.1 um in thickness) and excellent flow-through capabilities. TANs have recently been used to successfully produce high throughput dynamic membranes. However, their resistance to compaction is unknown and thought to be limited. A technique was developed to reinforce the TAN nanomaterial. Two binder materials were tested as reinforcing agents; SiO2 and AlH6O12P3. The binder-reinforced TANs were then packed into columns. Eleven columns having a 4 cm initial packing length were assembled. Tracer injection studies were performed to investigate the flow behavior and dispersion in these columns. SEM images were also taken to characterize the particles before and after compaction. The best results were obtained using a binding solution containing 7.5 (wt%) SiO2. The binder SiO2 offered a better resistance to compaction than the AlH6O12P3. The Peclet (Pe) number for the columns ranged from 22 to 648. When the content of SiO2 increased from 0 to 7.5 (wt%), the columns showed an increase in the Pe number. When SiO2 increased from 7.5 to 20 (wt%), the columns showed a decrease in the Pe number. However, AlH6O12P3 did not present any relation between the binder content and the Pe number. The results of this work demonstrate that reinforced TANs, are a new type of material that offers a packing with an open pore structure and improved channel connectivity. The new reinforced material offers considerable potential in many applications such as catalysis and separations over conventional materials. If they are used as packing materials in HPLC columns or packed bed reactors, they can contribute to a higher separation efficiency or an enhanced conversion rate or productivity, bringing more advantages and benefits than ordinary packing materials.