scholarly journals CFD simulation of solids suspension in stirred tanks: Review

2010 ◽  
Vol 64 (5) ◽  
pp. 365-374 ◽  
Author(s):  
Aoyi Ochieng ◽  
Mrice Onyango
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Concentration Distribution ◽  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Cfd Modeling ◽  
Small Scale ◽  
Stirred Tanks ◽  
Solids Concentration

Many chemical reactions are carried out using stirred tanks, and the efficiency of such systems depends on the quality of mixing, which has been a subject of research for many years. For solid-liquid mixing, traditionally the research efforts were geared towards determining mixing features such as off-bottom solid suspension using experimental techniques. In a few studies that focused on the determination of solids concentration distribution, some methods that have been used have not been accurate enough to account for some small scale flow mal-distribution such as the existence of dead zones. The present review shows that computational fluid dynamic (CFD) techniques can be used to simulate mixing features such as solids off-bottom suspension, solids concentration and particle size distribution and cloud height. Information on the effects of particle size and particle size distribution on the solids concentration distribution is still scarce. Advancement of the CFD modeling is towards coupling the physical and kinetic data to capture mixing and reaction at meso- and micro-scales. Solids residence time distribution is important for the design; however, the current CFD models do not predict this parameter. Some advances have been made in recent years to apply CFD simulation to systems that involve fermentation and anaerobic processes. In these systems, complex interaction between the biochemical process and the hydrodynamics is still not well understood. This is one of the areas that still need more attention.

CFD Simulation of Spouted Bed Working with a Size Distribution of Sand Particles: Segregation Aspects

2017 ◽  
Vol 899 ◽  
pp. 95-100
Author(s):  
Kássia Graciele dos Santos ◽  
L.V. Ferreira ◽  
Ricardo Correa Santana ◽  
Marcos Antonio de Souza Barrozo
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Cfd Simulation ◽  
Computational Simulation ◽  
Particle Diameter ◽  
Spouted Bed ◽  
Particle Segregation ◽  
Cfd Method ◽  
Mean Particle Diameter

Spouted bed simulations are usually performed using only one granular phase with a mean particle diameter representing the entire particle mixture, instead of a particle size distribution. In this study, the effect of the particle size distribution is accounted through the simulation of a mixture with five granular phases. The results showed that the particle segregation occurs. Larger particles are more concentrated in the upper region, while the smaller particles are preferably positioned in the lower region of the bed. Computational simulation using CFD method reproduced well the segregation experiments with different participle sizes of sand.

Hydrogeological Properties of Gypseous soils in South Africa

2019 ◽  
Vol 122 (3) ◽  
pp. 389-396
Author(s):  
M. Greyling ◽  
J.L. Van Rooy
Keyword(s):  
South Africa ◽  
Particle Size ◽  
Hydraulic Conductivity ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Small Scale ◽  
Prepared Sample ◽  
Brine Sample ◽  
Gypsum Content ◽  
Hydrogeological Properties

Abstract Gypseous soils occur in the western arid and semi-arid regions of South Africa and Namibia. These soils exhibit a complex nature and abnormal behaviour due to their gypsum content and as such they have become more prevalent in research. As these soils are finding more use in industry, an astute understanding of their hydrogeological properties and behaviour is required. Powdery gypseous soil samples collected from the Northern Cape (Geelvloer) and Western Cape (Rooiberg and R355) Provinces, as well as a prepared sample, are subject to XRD analysis, particle size distribution determination and falling-head permeability tests using both water and brine. The testing served as preliminary research to guide further studies into the topic. The prepared sample, with 19% fines, comprises 35% gypsum and 65% sand. Geelvloer samples, with 91.95% gypsum content, are comprised mostly of sand-sized particles with 45% fines. Rooiberg samples contain 75% fines with a slightly lower gypsum content of 83.25%, while R355 samples have 50% fines with 75.35% gypsum. It is generally understood that particle size distribution contributes to the hydraulic conductivity of soils, where a higher portion fines will result in a lower conductivity. In the case of gypseous soils, the solubility is of importance as well, as it may have long term effects. With the intent of evaluating the effect of the aforementioned factors on the hydraulic conductivity of gypseous soils in South Africa, the samples taken represent differences in particle size distribution and origin. Geelvloer had k-values in the order of 8.82×10-6 m/s, with the brine sample giving 9.43×10-6 m/s, while the k-values for Rooiberg and R355 were in the order of 3.90×10-6 m/s and 5.87×10-6 m/s, respectively. The brine resulted in 5.63×10-6 m/s for Rooiberg and 9.90×10-6 m/s for the R355 sample. The made sample, having less fines, had k values in the order of 2.15×10-5 m/s, and 4.19×10-5 m/s for the brine. The differences between the results are largely negligible and show that despite what is believed to influence the hydraulic conductivity, in the case of gypseous soils in South Africa, on a small scale, it remained unaffected.

scholarly journals Particle Lagrangian CFD Simulation and Experimental Characterization of the Rounding of Polymer Particles in a Downer Reactor with Direct Heating

Processes ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 916
Author(s):  
Juan S. Gómez Bonilla ◽  
Laura Unger ◽  
Jochen Schmidt ◽  
Wolfgang Peukert ◽  
Andreas Bück
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Residence Time ◽  
Cfd Simulation ◽  
Numerical Approach ◽  
Particle Dispersion ◽  
Direct Heating ◽  
Residence Time Distributions ◽  
Downer Reactor

Polypropylene (PP) powders are rounded at different conditions in a downer reactor with direct heating. The particles are fed through a single central tube, while the preheated sheath gas is fed coaxially surrounding the central aerosol jet. The influence of the process parameters on the quality of the powder product in terms of particle shape and size is analyzed by correlating the experimental results with the flow pattern, residence time distribution of the particles and temperature distribution predicted by computational fluid dynamics (CFD) simulations. An Eulerian–Lagrangian numerical approach is used to capture the effect of the particle size distribution on the particle dynamics and the degree of rounding. The simulation results reveal that inlet effects lead to inhomogeneous particle radial distributions along the total length of the downer. The configuration of particle/gas injection also leads to fast dispersion of the particles in direction of the wall and to particle segregation by size. Broad particle residence time distributions are obtained due to broad particle size distribution of the powders and the particles dispersion towards the wall. Lower mass flow ratios of aerosol to sheath gas are useful to reduce the particle dispersion and produce more homogenous residence time distributions. The particles’ residence time at temperatures above the polymer’s melting onset is determined from the simulations. This time accounts for the effective treatment (rounding) time of the particles. Clear correlations are observed between the numerically determined effective rounding time distributions and the progress of shape modification on the particles determined experimentally.

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