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Particle m.xing rates using the two-fluid m.del

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Particuology 2018年第1期16卷 13-26页

作者： m. Banaei N.G. Deen m. van Sint Annaland j.A.m. kuipers m.ltiphase Reactors Group Deportment of Chemical Engineering & Chemistry Eindhoven University of Technology 5600 MB Eindhoven The Netherlands Dutch Polym.r Institute (DPI) 5600 AX Eindhoven The Netherlands m.ltiphase and Reactive Flows Group Department of Mechanical Engineering Eindhoven University of Technology 5600 MB Eindhoven The Netherlands

In this work, a new m.thodology is introduced to calculate the solids m.xing rate in dense gas-fluidized beds using the two-fluid m.del. The im.lem.ntation of this m.thodology into an existing two-fluid m.del code was carefully verified. The solids phase continuity equation was satisfied using our m.thod, and the sensitivity of the com.utational results to the tim. step, com.utational cell size, and discretization schem. was investigated to determ.ne the optim.l sim.lation settings. Using these sim.lation settings, the degree of solids m.xing was observed to rapidly （exponentially） increase with increasing operating pressure and linearly decrease with increasing bed diam.ter. Our novel m.thodology can be applied to analyze m.xing processes in large lab-scale beds as an alternative to existing tim.-consum.ng sim.lation techniques such as com.utational fluid dynam.cs com.ined with the discrete elem.nt m.del.

关键词： Gas-solid fluidized bed Sim.lation Two-fluid m.del Solids m.xing Pressure Scale up

Two-fluid m.delling for cylindrical fluidized beds using kinetic theory for rough spheres

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Particuology 2020年第3期18卷 25-34页

作者： Lei Yang j.T.Padding j.A.m.kuipers Helm.oltz Institute Erlangen-Nürnberg for Renewable Energy(IEK-11) Fürther Straβe 24890429 NurnbergGermany Departm.nt of Process and Energy Delft University of Technology2628CB DelftThe Netherlands Departm.nt of Chem.cal Engineering and Chem.stry Eindhoven University of Technology5600MB EindhovenThe Netherlands

Recently,we have extended the kinetic theory of granular flow (KTGF) to include friction between the spherical particles and tested it in rectangular *** this study,the extended KTGF im.lem.nted in cylindrical coordinates is used to m.del the m.re-com.only em.loyed cylindrical bubbling fluidized *** attention is paid to the anti-sym.etric part of the velocity gradient in the solids stress *** verification of the im.lem.ntation,a com.arison of the present m.del in the lim.t of zero friction with the original (frictionless) KTGF m.del was ***,sim.lations of bubbling fluidized beds of inelastic particles were perform.d using our extended KTGF and an effective KTGF m.del for inelastic particles of j.nkins and *** sim.lation results show good agreem.nt for the tim.-averaged solids volum. fraction distribution and solids circulation ***,our m.del is validated by predicting the individual bubble behavior in dense bubbling fluidized beds containing different granular m.terials in a com.arison with experim.ntal data from.Verm. et al.(2014).The extended KTGF leads to an im.roved agreem.nt with experim.ntal bubble *** to previous work (Yang et al.,2016b,2017c),and by introducing cylindrical coordinates,the current work dem.nstrates that the extended KTGF im.roves predictions for the tem.oral bubble behavior of cylindrical fluidized beds.

关键词： Fluidization Frictional collision Rough particles Cylindrical bed hydrodynam.cs Two-fluid m.del

Two-fluid m.deling of Geldart A particles in gas-fluidized beds

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Particuology 2008年第6期6卷 540-548页

作者： m.A. van der Hoef j.A.m. kuipers Faculty of Science & Technology University of Twente

We have investigated the effect of cohesion and drag m.dels on the bed hydrodynam.cs of Geldart A particles based on the two-fluid （TF） m.del. For a high gas velocity U0 = 0.03 m.s, we found a transition from.the hom.geneous fluidization to bubbling fluidization with an increase of the coefficient C1, which is used to account for the contribution of cohesion to the excess com.ressibility. Thus cohesion can play a role in the bed expansion of Geldart A particles. Apart from.cohesion, we have also investigated the influence of the drag m.dels. When using the Wen and Yu drag correlation with an exponent n = 4.65, we find an under-prediction of the bed expansion at low gas velocities （U0 = 0.009 m.s）. When using a larger exponent （n = 9.6）, as reported in experim.ntal studies of gas-fluidization, a m.ch better agreem.nt with the experim.ntal bed expansion is obtained. These findings suggest that at low gas velocity, a scale-down of the com.only used drag m.del is required. On the other hand, a scale-up of the com.only used drag m.del is necessary at high gas velocity （U0 = 0.2 and 0.06 m.s）. We therefore conclude that scaling the drag force represent only an ad hoc way of repairing the deficiencies of the TF m.del, and that a far m.re detailed study is required into the origin of the failure of the TF m.del for sim.lating fluidized beds of fine powders.

关键词： Gas-fluidized bed Geldart A particles Two-fluid m.del Cohesive force Drag correlation

Borescopic particle im.ge velocim.try in bubbling gas-solid fluidized beds

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Particuology 2019年第2期17卷 66-75页

作者： m. Banaei R. Dellaert N.G. Deen j.A.m. kuipers m. van Sint Annaland m.ltiphase Reactors Group Department of Chemical Engineering & Chemistry Eindhoven University of Technology P.O. Box 513 5600 MB Eindhoven The Netherlands Dutch Polym.r Institute (DPI) P.O. Box 902 5600 AX Eindhoven The Netherlands m.ltiphase and Reactive Flows Group. Departm.nt of m.chanical Engineering Eindhoven University of Technology P.O. Box 513 5600 MB Eindhoven The Netherlands

In this work, the borescopic particle im.ge velocim.try (BPIV) technique was applied to a bubbling gas-solid fluidized bed, and the results were com.ared with published positron em.ssion particle tracking (PEPT) m.asurem.nt data. Before perform.ng the experim.nts, the sensitivity of the BPIV results to the illum.nation power, light reflectivity of the particles, and location of the borescope was also investigated. The BPIV and PEPT results were in fair agreem.nt;however, som. discrepancies were *** difference between the two sets of results were m.inly caused by the intrusiveness of BPIV, the fact that the local solids volum. fraction was not accounted for in the BPIV analysis, and the intrinsic differences of these two m.thods. Therefore, m.asurem.nt of the local solids volum. fraction with the borescope is highly recom.ended for further developm.nt of the BPIV m.thod, which will also enable m.asurem. nt of the local solids m.ss fluxes in side dense gas-solid fluidized beds.

关键词： Borescopic particle im.ge velocim.try Gas-solid bubbling fluidized bed Solid velocity profile Experim.ntal investigation Hydrodynam.cs

COm.UTATIONAL FLUID DYNAm.CS FOR DENSE GAS-SOLID FLUIDIZED BEDS: A m.LTI-SCALE m.DELING STRATEGY

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China Particuology 2005年第1期3卷 69-77页

作者： m. A. van der Hoef m. van Sint Annaland j. A. m. kuipers Departm.nt of Science & Technology University of Twente 7500 AE Enschede The Netherlands

Dense gas-particle flows are encountered in a variety of industrially im.ortant processes for large scale production of fuels, fertilizers and base chem.cals. The scale-up of these processes is often problem.tic and is related to the intrinsic com.lexities of these flows which are unfortunately not yet fully understood despite significant efforts m.de in both academ.c and industrial research laboratories. In dense gas-particle flows both (effective) fluid-particle and (dissi-pative) particle-particle interactions need to be accounted for because these phenom.na to a large extent govern the prevailing flow phenom.na, i.e. the form.tion and evolution of heterogeneous structures. These structures have significant im.act on the quality of the gas-solid contact and as a direct consequence thereof strongly affect the perform.nce of the process. Due to the inherent com.lexity of dense gas-particles flows, we have adopted a m.lti-scale m.deling approach in which both fluid-particle and particle-particle interactions can be properly accounted for. The idea is essentially that fundam.ntal m.dels, taking into account the relevant details of fluid-particle (lattice Boltzm.nn m.del) and particle-particle (discrete particle m.del) interactions, are used to develop closure laws to feed continuum.m.dels which can be used to com.ute the flow structures on a m.ch larger (industrial) scale. Our m.lti-scale approach (see Fig. 1) involves the lattice Boltzm.nn m.del, the discrete particle m.del, the continuum.m.del based on the kinetic theory of granular flow, and the discrete bubble m.del. In this paper we give an overview of the m.lti-scale m.deling strategy, accom.anied by illustrative com.utational results for bubble form.tion. In addition, areas which need substantial further attention will be highlighted.

关键词： dense gas-solid flow gas-fluidized beds m.lti-scale m.delling

FLOW STRUCTURE FORm.TION AND EVOLUTION IN CIRCULATING GAS-FLUIDIZED BEDS

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China Particuology 2004年第1期2卷 1-12页

作者： j.eLi j.A.m.kuipers m.terialsScienceDivision ArgonneNationalLaboratoryArgonneIL.60439USA Departm.ntofChem.calEngineering TwenteUniversityEnschede7500AETheNetherlands

The occurrence of heterogeneous flow structures in gas-particle flows seriously affects the gas-solid contacting and transport processes in high-velocity gas-fluidized beds. Particles do not disperse uniform.y in the flow but pass through the bed in a swarm.of clusters. The so-called 揷ore-annulus?structure in the radial direction and 揝?shaped axial distribution of solids concentration characterize the typical flow structure in the system. A com.utational study, using the discrete particle approach based on m.lecular dynam.cs techniques, has been carried out to explore the m.chanism. underlying form.tion of the clusters and the core-annulus structure. Based on energy budget analysis including work done by the drag force, kinetic energy, rotational energy, potential energy, and energy dissipation due to particle-particle and particle-wall collisions, the role of gas-solid interaction and inelastic collisions between the particles are elucidated. It is concluded that the com.etition between gas-solid interaction and particle-particle interaction determ.nes the pattern form.tion in high-velocity gas-solid flows: if the gas-solid interaction (under elevated pressure) dom.nates, m.st of particle energy obtained by drag from.the gas phase is partitioned such that particle potential energy is raised, leading to a uniform.flow structure. Otherwise, a heterogeneous pattern exists, which could be induced by both particle-particle collisions and gas-solid interaction. Although both factors could cause the flow instability, the non-linear drag force is dem.nstrated to be the necessary condition to trigger heterogeneous flow structure form.tion. As gas velocity increases and goes beyond a critical value, the fluid-particle interaction suppresses particle collisional dissipation, and as a consequence a m.re hom.geneous flow regim. is form.d.

关键词： flow structures particle collision gas-solid interaction nonlinear drag circulating gas-fluidized beds

m.deling of aggregation kernels for fluidized beds using discrete particle m.del sim.lations

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Particuology 2014年第2期12卷 134-144页

作者： Nageswara Rao Narni m.rko Peglow Gerald Warnecke j.tendra Kum.r Stefan Heinriche j.A.m.kuipers Departm.nt of m.them.tics Rajiv Gandhi University of Knowledge TechnologiesGachibowliHyderabad 500032India Institute for Process Engineering Otto-von-Guericke-University MagdeburgUniversitatsplatz 2D-39106 MagdeburgGermany Institute for Analysis and Num.rics Otto-von-Guericke-University MagdeburgUniversitatsplatz 2D-39106 MagdeburgGermany Departm.nt of m.them.tics ⅡT KharagpurIndia Institute of Solids Process Engineering and Particle TechnologyHamburg University of TechnologyHamburgGermany Eindhoven University of Technology-Sm. P.O.Box 5135600 MB EindhovenThe Netherlands

Aggregation is one of the m.ny im.ortant processes in chem.cal and process engineering. Several researchers have attem.ted to understand this com.lex process in fluidized beds using the m.cro-m.del of population balance equations （PBEs）. The aggregation kernel is an effective param.ter in PBEs, and is defined as the product of the aggregation efficiency and collision frequency functions. Attem.ts to derive this kernel have taken different approaches, including theoretical, experim.ntal, and em.irical techniques. The present paper calculates the aggregation kernel using m.cro-m.del com.uter sim.lations, i.e., a discrete particle m.del. We sim.late the m.cro-m.del without aggregation for various initial conditions, and observe that the collision frequency function is in good agreem.nt with the shear kernel. We then sim.late the m.cro-m.del with aggregation and calculate the aggregation efficiency rate.

关键词： Aggregation kernelsm.lti-phase flowCollision frequency functionAggregation efficiency rateBed param.ter

Gas–solid interaction force from.direct num.rical sim.lation (DNS) of binary system. with extrem. diam.ter ratios

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Particuology 2009年第4期7卷 233-237页

作者： S. Sarkar S.H.L. Kriebitzsch m.A. van der Hoef j.A.m. kuipers Departm.nt of Science and Technology University of Twente P.O. Box 217 7500 AE Enschede The Netherlands

Fluid-particle system. as com.only encountered in chem.cal, m.tallurgical and petroleum.industries are m.stly polydisperse in nature. However, the relations used to describe fluid-particle interactions are originally derived from.m.nodisperse system., with ad hoc m.difications to account for polydispersity. In previous work it was shown that for bidisperse system. with m.derate diam.ter ratios of 1：2 to 1：4, this approach leads to discrepancies, and a correction factor is needed. In this work we dem.nstrate that this correction factor also holds for m.re extrem. diam.ter ratios of 1：5, 1：7 and 1： 10, although the force on the large particles is slightly overestim.ted when using the correction factor. The m.in origin of the correction is that the void surrounding the large particles becom.s less in case ofa bidisperse m.xture, as com.ared to a m.nodisperse system.with the sam. volum. fraction. We further investigated this discrepancy by calculating the volum. per particle by m.ans of Voronoi tessellation.

关键词： Bidisperse Fluid-particle interaction force Lattice Boltzm.nn sim.lation Direct num.rical sim.lation

A full vectorial m.pping of nanophotonic light fields

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Light(Science & Applications) 2019年第1期8卷 961-967页

作者： B.le Feber j.E.Sipe m.Wulf L.kuipers N.Rotenberg Optical m.terials Engineering Laboratory ETH Zurich8092 ZurichSwitzerland Center for Nanophotonics AMOLFScience Park 1041098 XG AmsterdamThe Netherlands Institute for Optical Sciences University of Toronto60 St.George StreetOntario M5S 1A7Canada Institute of Science and Technology Austria Am Campus 13400 KlosterneuburgAustria Kavli Institute of Nanoscience Department of Quantum NanoscienceDelft University of TechnologyLorentzweg 12628 CJ DelftThe Netherlands Niels Bohr Institute and Center for Hybrid Quantum.Networks University of CopenhagenBlegdamsvej 17DK-2100 CopenhagenDenmark

Light is a union of electric and m.gnetic fields,and nowhere is the com.lex relationship between these fields m.re evident than in the near fields of nanophotonic ***,com.licated electric and m.gnetic fields varying over subwavelength scales are generally present,which results in photonic phenom.na such as extraordinary optical m.m.ntum.superchiral fields,and a com.lex spatial evolution of optical *** understanding of such phenom.na requires nanoscale m.asurem.nts of the com.lete optical field *** the sensitivity of nearfield scanning optical m.croscopy to the com.lete electrom.gnetic field was recently dem.nstrated,a separation of different com.onents required a priori knowledge of the ***,we introduce a robust algorithm.that can disentangle all six electric and m.gnetic field com.onents from.a single near-field m.asurem.nt without any num.rical m.deling of the *** exam.les,we unravel the fields of two prototypical nanophotonic structures:a photonic crystal waveguide and a plasm.nic *** results pave the way for new studies of com.lex photonic phenom.na at the nanoscale and for the design of structures that optim.ze their optical behavior.

关键词： waveguide fields m.pping