scholarly journals Modelling density segregation in flowing bidisperse granular materials

2016 ◽  
Vol 472 (2191) ◽  
pp. 20150856 ◽  
Author(s):  
Hongyi Xiao ◽  
Paul B. Umbanhowar ◽  
Julio M. Ottino ◽  
Richard M. Lueptow
Keyword(s):  
Particle Concentration ◽  
Practical Interest ◽  
Industrial Processes ◽  
Dem Simulations ◽  
Granular Mixtures ◽  
Theoretical Predictions ◽  
Local Shear ◽  
Density Ratios ◽  
Kinematic Information ◽  
Modelling Approach

Preventing segregation in flowing granular mixtures is an ongoing challenge for industrial processes that involve the handling of bulk solids. A recent continuum-based modelling approach accurately predicts spatial concentration fields in a variety of flow geometries for mixtures varying in particle size. This approach captures the interplay between advection, diffusion and segregation using kinematic information obtained from experiments and/or discrete element method (DEM) simulations combined with an empirically determined relation for the segregation velocity. Here, we extend the model to include density-driven segregation, thereby validating the approach for the two important cases of practical interest. DEM simulations of density bidisperse flows of mono-sized particles in a quasi-two-dimensional-bounded heap were performed to determine the dependence of the density-driven segregation velocity on local shear rate and particle concentration. The model yields theoretical predictions of segregation patterns that quantitatively match the DEM simulations over a range of density ratios and flow rates. Matching experiments reproduce the segregation patterns and quantitative segregation profiles obtained in both the simulations and the model, thereby demonstrating that the modelling approach captures the essential physics of density-driven segregation in granular heap flow.

scholarly journals Designing non-segregating granular mixtures

2021 ◽  
Vol 249 ◽  
pp. 03011
Author(s):  
Yifei Duan ◽  
Paul B. Umbanhowar ◽  
Richard M. Lueptow
Keyword(s):  
Particle Size ◽  
Equilibrium Condition ◽  
Density Ratio ◽  
Heavy Particles ◽  
Dem Simulations ◽  
Particle Size Ratio ◽  
Granular Mixtures ◽  
Mixture Concentration ◽  
Large Particles ◽  
Density Ratios

In dense flowing bidisperse particle mixtures varying in size or density alone, large particles rise (driven by percolation) and heavy particles sink (driven by buoyancy). When the two particle species differ from each other in both size and density, the two segregation mechanisms either enhance (large/light and small/heavy) or oppose (large/heavy and small/light) each other. In the latter case, an equilibrium condition exists in which the two mechanisms balance and the particles no longer segregate. This leads to a methodology to design non-segregating particle mixtures by specifying particle size ratio, density ratio, and mixture concentration to achieve the equilibrium condition. Using DEM simulations of quasi-2D bounded heap flow, we show that segregation is significantly reduced for particle mixtures near the equilibrium condition. In addition, the rise-sink transition for a range of particle size and density ratios matches the predictions of the combined size and density segregation model.

Modelling Gas Processing Unit: An Inter-disciplinary Approach Based on Petri Nets

2008 ◽  
Vol 59 (7) ◽  
Author(s):  
Sanda Florentina Mihalache
Keyword(s):  
Industrial Process ◽  
Industrial Processes ◽  
Processing Unit ◽  
Industrial System ◽  
Modeling Framework ◽  
Gas Processing ◽  
Human Interactions ◽  
Modelling Method ◽  
Effective Representation ◽  
Modelling Approach

A modelling approach that will facilitate an in-depth understanding of the interactions of the different phenomena, human interactions and environmental factors constituting �real world� industrial processes is presented. An important industrial system such as Gas Processing Unit (GPU) have inter-related internal process activities coexisting with external events and requires a real time inter-disciplinary approach to model them. This modeling framework is based on identifying as modules, the part of processes that have interactions and can be considered active participants in overall behaviour. The selected initial set of modules are structured as Petri net models and made to interact iteratively to provide process states of the system. The modeling goal is accomplished by identifying the evolution of the process states as a means of effective representation of the �actual running�� of the industrial process. The paper discusses the function and the implementation of the modelling method as applicable to the industrial case of GPU.

scholarly journals Systematic Experimental Investigation of Segregation Direction and Layer Inversion in Binary Liquid-Fluidized Bed

Processes ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 177
Author(s):  
Alberto Di Renzo ◽  
Giacomo Rito ◽  
Francesco P. Di Maio
Keyword(s):  
Experimental Investigation ◽  
Operating Conditions ◽  
Industrial Processes ◽  
Process Unit ◽  
Separation Processes ◽  
Solids Concentration ◽  
Expansion Range ◽  
Surface Expansion ◽  
Density Ratios ◽  
Inversion Phenomenon

Multi-component liquid-fluidized beds are encountered in a variety of industrial processes. Often, segregation severely affects the performance of the process unit. Unfortunately, size-driven and density-driven separation processes may occur with a complex interplay, showing prevailing mechanisms that change with the operating conditions. For example, when the solids exhibit contrasting differences in size and density, even the direction of segregation can turn out hard to predict, giving rise for some systems to the so-called “layer inversion phenomenon”. A systematic experimental investigation is presented on 14 different binary beds composed of glass beads and ABS spheres with different size and density ratios and different bed composition. The analysis allows assessing the reliability of a model for predicting the segregation direction of fluidized binary beds (the Particle Segregation Model, PSM). By measurements of the solids’ concentration at the surface, expansion/segregation properties and the inversion voidage are compared with the PSM predictions, offering a direct means of model validation. Both the segregation direction throughout the expansion range and the value of the inversion voidage are compared. Extensive qualitative agreement is obtained for 12 out of 14 fluidized mixtures. Quantitatively, the average discrepancy between predicted and measured inversion voidage is below 5%, with a maximum of 17%.

scholarly journals The WAGGS project-III. Discrepant mass-to-light ratios of Galactic globular clusters at high metallicity

2020 ◽  
Vol 492 (3) ◽  
pp. 3859-3871 ◽  
Author(s):  
H Dalgleish ◽  
S Kamann ◽  
C Usher ◽  
H Baumgardt ◽  
N Bastian ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Milky Way ◽  
Population Models ◽  
Theoretical Predictions ◽  
Field Unit ◽  
Stellar Masses ◽  
Kinematic Information ◽  
High Metallicity ◽  
Integral Field

ABSTRACT Observed mass-to-light ratios (M/L) of metal-rich globular clusters (GCs) disagree with theoretical predictions. This discrepancy is of fundamental importance since stellar population models provide the stellar masses that underpin most of extragalactic astronomy, near and far. We have derived radial velocities for 1622 stars located in the centres of 59 Milky Way GCs – 12 of which have no previous kinematic information – using integral-field unit data from the WAGGS project. Using N-body models, we determine dynamical masses and M/LV for the studied clusters. Our sample includes NGC 6528 and NGC 6553, which extend the metallicity range of GCs with measured M/L up to [Fe/H] ∼ −0.1 dex. We find that metal-rich clusters have M/LV more than two times lower than what is predicted by simple stellar population models. This confirms that the discrepant M/L–[Fe/H] relation remains a serious concern. We explore how our findings relate to previous observations, and the potential causes for the divergence, which we conclude is most likely due to dynamical effects.

Universality of finger growth in two-dimensional Rayleigh–Taylor and Richtmyer–Meshkov instabilities with all density ratios

2015 ◽  
Vol 786 ◽  
pp. 47-61 ◽  
Author(s):  
Qiang Zhang ◽  
Wenxuan Guo
Keyword(s):  
Density Ratio ◽  
Classical Problem ◽  
Significant Feature ◽  
Dimensional System ◽  
Surprising Result ◽  
Universal Curve ◽  
Two Dimensional ◽  
Past Half Century ◽  
Theoretical Predictions ◽  
Density Ratios

Interfacial fluid mixing driven by an external acceleration or a shock wave are common phenomena known as Rayleigh–Taylor instability and Richtmyer–Meshkov instability, respectively. The most significant feature of these instabilities is the penetrations of heavy (light) fluid into light (heavy) fluid known as spikes (bubbles). The study of the growth rate of these fingers is a classical problem in fundamental science and has important applications. Research on this topic has been very active over the past half-century. In contrast to the well-known phenomena that spikes and bubbles can have quantitatively, even qualitatively, different behaviours, we report a surprising result for fingers in a two-dimensional system: in terms of scaled dimensionless variables, all spikes and bubbles at any density ratio closely follow a universal curve, up through a pre-asymptotic stage. Such universality holds not only among bubbles and among spikes of different density ratios, but also between bubbles and spikes of different density ratios. The data from numerical simulations show good agreement with our theoretical predictions.

Modelling Approach for a Hydrolysis Reactor for the Ammonia Production in Maritime SCR Applications

2017 ◽  
Author(s):  
Katrin Johe ◽  
Thomas Sattelmayer
Keyword(s):  
System Performance ◽  
Catalytic Reduction ◽  
Ammonia Concentration ◽  
Operating Conditions ◽  
Urea Solution ◽  
Step Method ◽  
Proposed Model ◽  
Theoretical Predictions ◽  
Critical Process ◽  
Modelling Approach

The catalytic generation of ammonia from a liquid urea solution is a critical process determining the performance of SCR (Selective Catalytic Reduction) systems. Solid deposits on the catalyst surface from the decomposition of urea have to be avoided, as this leads to reduced system performance or even failure. At present, reactor design is often empirical, which poses a risk for costly iterations due to insufficient system performance. The presented research project proposed a performance prediction and modelling approach for SCR hydrolysis reactors generating ammonia from urea. Different configurations of hydrolysis reactors were investigated experimentally. Ammonia concentration measurements provided information about parameters influencing the decomposition of urea and the system performance. The evaporation of urea between injection and interaction with the catalyst was identified as the critical process driving the susceptibility to deposit formation. The spray of urea solution was characterised in terms of velocity distribution by means of particle-image velocimetry. Results were compared with theoretical predictions and calculation options for processes in the reactor were determined. Numerical simulation was used as an additional design and optimisation tool of the proposed model. The modelling approach is presented by a step-by-step method which takes into account design constraints and operating conditions for hydrolysis reactors.

An experimental study of the motion of concentrated suspensions in two-dimensional channel flow. Part 1. Monodisperse systems

1998 ◽  
Vol 363 ◽  
pp. 25-56 ◽  
Author(s):  
M. K. LYON ◽  
L. G. LEAL
Keyword(s):  
Experimental Data ◽  
Particle Velocity ◽  
Particle Concentration ◽  
Rectangular Channel ◽  
Particle Diameter ◽  
Index Of Refraction ◽  
Model Parameters ◽  
Diffusive Flux ◽  
Theoretical Predictions ◽  
Flux Model

A modified laser-Doppler velocimetry method is utilized to measure fully developed particle velocity and concentration profiles, as well as the mean-square amplitudes of velocity fluctuations (i.e. one component of the so-called particle temperature), for concentrated monodisperse suspensions across the narrow gap of a rectangular channel. A stable index-of-refraction match of the suspending and particulate phases in conjunction with short-focal-length focusing optics has enabled data acquisition up to particle volume fractions of 0.50. In general, the particle concentration distributions possess a maximum near the channel centreline and a minimum at the channel walls. Coupled to these concentration distributions were blunted velocity profiles, and particle velocity fluctuation distributions that had a sharp maximum at gap positions approximately 80% of the way from the channel axis towards the walls. The particle velocity distributions were consistent with the absence of slip between particles and the suspending fluid.The experimental data were compared with theoretical predictions from the diffusive flux model (Leighton & Acrivos 1987; Phillips et al. 1992), a model due to Mills & Snabre (1995), and the suspensions balance model (McTigue & Jenkins 1992; Nott & Brady 1994). The influence of bulk particle concentration, suspension volumetric flow rate, and ratio of channel gap width to particle diameter on the fully developed profiles was qualitatively consistent with the theoretical predictions from all three models. For the diffusive flux and suspension balance models, we used both literature values for model parameters, and values obtained from a best fit to our entire set of experimental data. Overall, the Mills & Snabre and suspension balance models were found to provide a better quantitative fit to the experimental data than the diffusive flux model.

scholarly journals The steady aerodynamics of aerofoils with porosity gradients

2017 ◽  
Vol 473 (2205) ◽  
pp. 20170266 ◽  
Author(s):  
Rozhin Hajian ◽  
Justin W. Jaworski
Keyword(s):  
Noise Suppression ◽  
Hilbert Problem ◽  
Practical Interest ◽  
Hölder Condition ◽  
Hölder Continuous ◽  
Porosity Distribution ◽  
Minimal Impact ◽  
Aerodynamic Loads ◽  
Formal Restriction ◽  
Theoretical Predictions

This theoretical study determines the aerodynamic loads on an aerofoil with a prescribed porosity distribution in a steady incompressible flow. A Darcy porosity condition on the aerofoil surface furnishes a Fredholm integral equation for the pressure distribution, which is solved exactly and generally as a Riemann–Hilbert problem provided that the porosity distribution is Hölder-continuous. The Hölder condition includes as a subset any continuously differentiable porosity distributions that may be of practical interest. This formal restriction on the analysis is examined by a class of differentiable porosity distributions that approach a piecewise, discontinuous function in a certain parametric limit. The Hölder-continuous solution is verified in this limit against analytical results for partially porous aerofoils in the literature. Finally, a comparison made between the new theoretical predictions and experimental measurements of SD7003 aerofoils presented in the literature. Results from this analysis may be integrated into a theoretical framework to optimize turbulence noise suppression with minimal impact to aerodynamic performance.

scholarly journals How to Cope with Climate’s Complexity?

2009 ◽  
Vol 17 (2) ◽  
pp. 371-402
Author(s):  
Michel Crucifix
Keyword(s):  
Dynamical Systems ◽  
Bayesian Statistics ◽  
Climate Models ◽  
Practical Interest ◽  
Dissipative Structures ◽  
Macroscopic Scale ◽  
Linear Dynamical Systems ◽  
Ice Caps ◽  
Vast Range ◽  
Modelling Approach

Climate exhibits a vast range of dissipative structures. Some have characteristic times of a few days; others evolve over thousands of years. All these structures are interdependent; in other words, they communicate. It is often considered that the only way to cope with climate complexity is to integrate the equations of atmospheric and oceanic motion with the finest possible mesh. Is this the sole strategy? Aren’t we missing another characteristic of the climate system: its ability to destroy and generate information at the macroscopic scale? Paleoclimatologists consider that much of this information is present in palaeoclimate archives. It is therefore natural to build climate models such as to get the most of these archives. The strategy proposed here is based on Bayesian statistics and low-order non-linear dynamical systems, in a modelling approach that explicitly includes the effects of uncertainties. Its practical interest is illustrated through the problem of the timing of the next great glaciation. Is glacial inception overdue or do we need to wait for another 50,000 years before ice caps grow again? Our results indicate a glaciation inception in 50,000 years.

Sign in / Sign up

Export Citation Format

Share Document