Local Structure Effects on Pressure Drop in Slender Fixed Beds of Spheres

Abstract

Ing. Matthias Kraume on the occasion of his 65th birthday For slender fixed beds, the void fraction and flow properties are complex topics. Different factors can influence the local bed structure. For statistical analysis, 2800 fixed beds have been generated and the impact of friction factor and reactor-toparticle diameter ratio on the distribution has been shown. With particle-resolved computational fluid dynamics, all local structure effects are taken into account for the flow simulations. Pressure drop measurements and simulations showed that these effects can lead to areas with low flow resistance, leading to overestimated pressure drop by typical correlations up to 85 %.

Local Structure Effects on Heat Transfer in Very Low Tube-to-Particle Diameter Ratio Fixed Beds of Spheres

“…It is easily shown from this that there is a maximum in ε at N = 1.67, as mentioned by Govindarao et al 26 This is in good agreement with the data presented by von Seckendorff et al 19 and Flaischlen et al 21 and reproduced in Figure 2. At this point, the increase in void fraction from the larger wall channels is countered by the increasingly compact packing of spheres in the axial direction, and as the effect of the axial packing starts to dominate, the voidage starts to decrease.…”

“…The increase in A wf that is seen there is due to decreased channels at the tube wall which reduce wall by-pass flow. At N = 2, there is a fairly rapid change from high to low Pe rf (∞) with only a small change in void fraction, similar to the result seen for pressure drop by Flaischlen et al 21 This strongly suggests that the flow pattern has changed considerably due to a As N increases from 2, Pe rf (∞) also increases as the structure of alternating pairs breaks down forming channels, especially at the bed center, termed "ducts" by von Seckendorff et al 19 Void fraction ε continues to decrease due to more compact packing in the axial direction, but then appears to level out. There are suggestions of local minima and maxima, but these are not clear from the data in Figure 2.…”

“…Further insight into this structure-based behavior was provided by Flaischlen et al 21 They made experimental measurements of ε and ΔP in beds of spheres of N = 1.51, 2.68, and 3.02 and compared to computer-generated beds at those values, and at N = 2 and 2.7. They also plotted ε vs N, for the range 1 ≤ N ≤ 5, from their own results and those of Bufe and Brenner 17 and von Seckendorff et al 19 Their results showed that void fractions from computer-generated packings could vary significantly at the same N, and that a decrease in the friction coefficient used in the rigid body algorithm gave more ordered structures with lower ε, and non-Gaussian right-tailed distributions of ε.…”

Influence of Foam Morphology on Flow and Heat Transport in a Random Packed Bed with Metallic Foam Pellets—An Investigation Using CFD

“…Slender packed bed reactors ( ) are the preferred reactor type for an efficient removal or addition of heat, i.e., for highly exothermic or endothermic catalytic reactions. They have complex transport characteristics due to local bed structure effects [ 10 ], different flow regimes, and their interaction between different heat transfer mechanisms [ 11 ]. In addition to shape and size, the pelletized foams offer extra design flexibility due to their morphologies, especially cell size and porosity, as shown in Figure 1 .…”

Young Scientists – Juniorprofessor Gregor D. Wehinger stellt sich vor

“…B. Darstellungsprobleme komplexer Partikel und lange Rechenzeiten, umgehen bei gleichzeitiger Präzision der erstellten Betten. In einer kürzlich veröffentlichten Arbeit untersuchten wir die lokale Bettstruktur und die daraus resultierende Strömung mit PRCFD und Experimenten 8. Für gewisse D / d ‐Verhältnisse ergeben sich sehr regelmäßige Bettstrukturen, die erhebliche Strömungskanäle ausbilden.…”