The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Jesse Zhu - One of the best experts on this subject based on the ideXlab platform.
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prediction of dense phase Voidage for group c fluidized bed reactor
Chemical Engineering Journal, 2020Co-Authors: Yandaizi Zhou, Jesse ZhuAbstract:Abstract Group C+ fluidized bed reactor exhibited better reactor performance than conventional fluidized bed reactors, due to the larger specific surface area of the catalysts and the more homogeneous fluidization, especially the extraordinary dense phase expansion which contributes to higher gas–solid contact efficiency. As a critical parameter affecting the reactor performance, the dense phase Voidage (ed) was thoroughly characterized and general correlations for predicting ed were derived based on both Richardson-Zaki and Kozeny-Carman approaches. In addition, a new method for predicting the minimum fluidization velocity of Group C+ particles with the consideration of the particle cohesion was proposed. The bed Voidage at minimum fluidization (emf) and the maximum dense phase Voidage (ed,max) were shown to correlate well with a dimensionless cohesion index (σ*). All these new correlations showed good agreements with the experimental data for various types of Group C+ particles.
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A new definition of bed expansion index and Voidage for fluidized biofilm-coated particles
Chemical Engineering Journal, 2012Co-Authors: Mehran Andalib, Jesse Zhu, George NakhlaAbstract:Abstract Experimental data available in the literature for bed Voidage and bed expansion index of biofilm-coated particles in a fluidized bed was extracted, sorted and used to study the validation of the proposed bed expansion index equations in the literature. Drag coefficients of biofilm-coated particles for all the aforementioned data were calculated using a new proposed equation [1] that describes drag forces as a function of Archimedes numbers. Archimedes number was proposed to be superior to Reynolds number for bed expansion definition. New equations based on Archimedes number and physical properties of biofilm-coated particles were proposed to calculate the bed expansion index of fluidized biofilm-coated particles as well as bed Voidage in fluidized bed bioreactors. The new equations predicted the existing experimental bed expansion index and Voidage with less standard average error than all other literature equations that related bed expansion to Reynolds number.
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Voidage profiles in a circulating fluidized bed of square cross section
Chemical Engineering Science, 1994Co-Authors: J Zhou, John R Grace, S Qin, C M H Brereton, C J Lim, Jesse ZhuAbstract:Abstract Using an optical fiber particle concentration measuring system, an extensive study was carried out of Voidage profiles in a circulating fluidized bed riser of square cross-section. Both lateral and axial Voidage profiles were obtained. Particle concentration is not necessarily lowest at the axis of the riser, but may go through a minimum between the wall and the axis. The study also reveals the influence of the corners on the Voidage profile. Because of the exit effect, profiles of Voidage at the top of the riser are asymmetric. Bimodal and even trimodal probability distributions of particle concentration are found. The intermittency index is used to characterize the heterogeneity/homogeneity of the flow.
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measurements of Voidage profiles in spouted beds
Canadian Journal of Chemical Engineering, 1994Co-Authors: C J Lim, Jesse Zhu, John R Grace, S Z QznAbstract:A fibre optic probe has been used to measure Voidage profiles in the fountain, spout and annulus of spouted beds. The Voidage in most of the annulus was found to be somewhat higher than the loose-packed Voidage and increased with increasing spouting gas flow rate, contrary to usual assumptions. There is a denser region in the annulus where the Voidage was a little lower than the loose-packed bed Voidage. In the core of the fountain, the Voidage decreased with height for low spouting gas flow rate, consistent with the model of Grace and Mathur (1978); however, at higher gas flow rate, it first increased with height and then decreased towards the fountain top. The radial profiles of local Voidage were roughly parabolic in the lower portion of the spout and blunt in the upper portion. On a utilise une sonde a fibres optiques pour mesurer les profils de vide dans la fontaine, le jet et l'espace annulaire des lits jaillissants. Dans la majorite des cas, le vide dans l'espace annulaire s'est avere plus eleve que dans les lits moins densement garnis et augmente avec le debit de gaz jaillissant, contrairement aux hypotheses habituelles. I1 existe une region plus dense dans l'espace annulaire ou le vide est Iegerement plus faible que dans les lits moins densement garnis. Dans le coeur de la fontaine, le vide diminue avec la hauteur pour un faible debit de gaz jaillissant, ce qui concorde avec le modele de Grace et Mathur (1978); cependant, a des debits de gaz eleves, le vide augmente dans un premier temps avec la hauteur puis diminue lorsqu'on arrive a I'extremite superieure de la fontaine. Les profils radiaux du vide local sont a peu pres paraboliques dans la partie inferieure du jet et plats dans la partie superieure.
Ugur Tüzün - One of the best experts on this subject based on the ideXlab platform.
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Discharge and transport of nearly buoyant granular solids in liquids Part I: Tomographic study of the interstitial Voidage effects governing flow regimes
Chemical Engineering Science, 1998Co-Authors: S. Faderani, Ugur Tüzün, D.l.o. Smith, Rex B. ThorpeAbstract:The interstitial Voidage profiles prevailing in static and flowing beds of nearly buoyant granular materials in aqueous solutions are measured directly by scanning with the use of γ-ray tomography, the contents of a mass-flow hopper and vertical stand-pipe system. In a series of ‘start-stop’ flow and ‘steady-state” flow experiments, horizontal line profiles, and radial profiles of interstitial Voidage are produced at different heights within the conical hopper and vertical stand-pipe sections. The Voidage profiles obtained within the static beds prior to the onset of discharge are compared with the profiles measured at the same heights during batch discharge of the hopper contents. Furthermore, the plane mean values of the flowing bed Voidage are calculated at different heights using the cross-sectional profiles of Voidage obtained under the steady discharge condition. The resulting vertical profiles of plane-mean Voidage obtained with three different food analogues are found to reveal hitherto unavailable and highly significant new information about the transitions accompanying flow between the packed-bed and settling-suspension states as a function of the mixture discharge rates and the single particle properties, such as particle size, shape, and particle density. The experimental results presented here are subsequently incorporated into simple mean-field models (ignoring interparticle and wall frictional effects) which are used to calculate slip velocities of the particle phase, interstitial pore pressures due to the fluid phase, as well as the observed variation of the discharged solids concentration with the mixture discharge rate. The model predictions are compared with experimental measurements in Faderani et al. (1998, Chem. Engng Sci.53, 575).
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A tomographic study of Voidage profiles in axially symmetric granular flows
Chemical Engineering Science, 1993Co-Authors: M.e. Hosseini-ashrafi, Ugur TüzünAbstract:Abstract A specially constructed multiple-source scanner is used to produce consecutive tomographic images of the horizontal planes at different heights of the granular beds flowing in both cylindrical and conical vessels. In a series of experiments involving batch discharge of mono-sized and binary fills of materials, the transients in the cross-sectional Voidage profiles are quantified to within a spatial accuracy of 1 mm in Cartesian and 1° in polar coordinates in time steps of 5–10 s. The plane mean values of the Voidage are calculated in each case to produce height profiles of Voidage within the vessel at different stages of discharge. The height profiles of Voidage obtained within a converging flow field such as that occurring in a conical vessel are all found to exhibit a well-defined maximum value close to the discharge orifice. Following the flow initiation, the position of the Voidage maximum is found to move up the cone, resulting in a counter-current Voidage wave front accompanying the steady material discharge from the hopper orifice. In a vessel with a cylindrical top section, the plane mean Voidage is found to reach its minimum value above the plane of bin—hopper transition.
J.p. Van Der Hoek - One of the best experts on this subject based on the ideXlab platform.
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Accurate Voidage prediction in fluidisation systems for full-scale drinking water pellet softening reactors using data driven models
Journal of Water Process Engineering, 2020Co-Authors: O.j.i. Kramer, P.j. De Moel, Jt Johan Padding, E.t. Baars, Y.m.f. El Hasadi, Edo S. Boek, J.p. Van Der HoekAbstract:Abstract In full-scale drinking water production plants in the Netherlands, central softening is widely used for reasons related to public health, client comfort, and economic and environmental benefits. Almost 500 million cubic meters of water is softened annually through seeded crystallisation in fluidised bed reactors. The societal call for a circular economy has put pressure on this treatment process to become more sustainable. By optimising relevant process conditions, the consumption of chemicals can be reduced, and raw materials reused. Optimal process conditions are feasible if the specific crystallisation surface area in the fluidised bed is large enough to support the performance of the seeded crystallisation process. To determine the specific surface area, crucial variables including Voidage and particle size must be known. Numerous models can be found in the literature to estimate the Voidage in liquid-solid fluidisation processes. Many of these models are based on semi-empirical porous-media-based drag relations like Ergun or semi-empirical terminal-settling based models such as Richardson-Zaki and fitted for monodisperse, almost perfectly round particles. In this study, we present new Voidage prediction models based on accurate data obtained from elaborate pilot plant experiments and non-linear symbolic regression methods. The models were compared with the most popular Voidage prediction models using different statistical methods. An explicit model for Voidage estimation based on the dimensionless Reynolds and Froude numbers is presented here that can be used for a wide range of particle sizes, fluid velocities and temperatures and that can therefore be directly used in water treatment processes such as drinking water pellet softening. The advantage of this model is that there is no need for applying numerical solutions; therefore, it can be explicitly implemented. The prediction errors for classical models from the literature lie between 2.7 % and 11.4 %. With our new model, the Voidage prediction error is reduced to 1.9 %.
Domingo Santana - One of the best experts on this subject based on the ideXlab platform.
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Voidage distribution around bubbles in a fluidized bed: Influence on throughflow
Powder Technology, 2010Co-Authors: José Antonio Almendros-ibáñez, David Pallarès, F. Johnsson, Domingo SantanaAbstract:In this work, a new method for measuring void fraction distribution around endogenous bubbles in a 2D fluidized bed is presented. The technique is based on illuminating a transparent-wall 2-dimensional bed with diffuse light from the rear and recording the distribution of light that penetrates the bed. The recording is made with a high speed video-camera, which gives frames with grey level corresponding to the light penetration and from which the Voidage distribution around the bubbles can be determined. In this way, Voidage distribution in the region very close to the bubble contour (r/Rb≲1.2) is obtained, which was not possible in previous studies due to limitations in spatial resolution. A correlation is proposed for the Voidage at the contour of the bubble, with the Voidage depending on the radial position and the polar angle ε(r, θ). In addition, the effect of the Voidage distribution on the throughflow crossing the bubbles was studied and an increase of 20% was determined for the average bubble geometry of the more than 100 bubbles analysedPublicad
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Voidage distribution around bubbles in a fluidized bed: Influence on throughflow
Powder Technology, 2009Co-Authors: José Antonio Almendros-ibáñez, Filip Johnsson, David Pallarès, Domingo SantanaAbstract:Abstract In this work, a new method for measuring void fraction distribution around endogenous bubbles in a 2D fluidized bed is presented. The technique is based on illuminating a transparent-wall 2-dimensional bed with diffuse light from the rear and recording the distribution of light that penetrates the bed. The recording is made with a high speed video-camera, which gives frames with grey level corresponding to the light penetration and from which the Voidage distribution around the bubbles can be determined. In this way, Voidage distribution in the region very close to the bubble contour ( r / R b ≲ 1.2) is obtained, which was not possible in previous studies due to limitations in spatial resolution. A correlation is proposed for the Voidage at the contour of the bubble, with the Voidage depending on the radial position and the polar angle e ( r , θ ). In addition, the effect of the Voidage distribution on the throughflow crossing the bubbles was studied and an increase of 20% was determined for the average bubble geometry of the more than 100 bubbles analysed.
Nicholas Willoughby - One of the best experts on this subject based on the ideXlab platform.
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experimental measurement of particle size distribution and Voidage in an expanded bed adsorption system
Biotechnology and Bioengineering, 2000Co-Authors: Nicholas Willoughby, Rolf A. Hjorth, N J TitchenerhookerAbstract:This paper presents an experimental analysis of matrix bead size distribution and Voidage variations with axial height in an expanded bed adsorption system. Use of a specially constructed expanded bed with side ports has enabled sampling from within the expanded bed along the vertical axis. Particles removed from within the bed were measured for their size distributions. Residence time distribution studies were used to estimate bed Voidage. Measurements of axial and radial particle size distributions and axial Voidage distribution have been made at different flow rates. Particle size was found to be radially constant, indicating constant stratification in the column. The particle size was found to decrease with increasing axial height. Voidage increased with axial height from a settled bed value of 0.39 to approaching unity for high liquid velocities and increased at a constant axial position with increased flowrate. This information provides key insight into bed stability and data for the improved modeling of this important unit operation. (C) 2000 John Wiley & Sons, Inc.
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Experimental measurement of particle size distribution and Voidage in an expanded bed adsorption system.
Biotechnology and bioengineering, 2000Co-Authors: Nicholas Willoughby, Rolf Hjorth, Nigel J. Titchener-hookerAbstract:This paper presents an experimental analysis of matrix bead size distribution and Voidage variations with axial height in an expanded bed adsorption system. Use of a specially constructed expanded bed with side ports has enabled sampling from within the expanded bed along the vertical axis. Particles removed from within the bed were measured for their size distributions. Residence time distribution studies were used to estimate bed Voidage. Measurements of axial and radial particle size distributions and axial Voidage distribution have been made at different flow rates. Particle size was found to be radially constant, indicating constant stratification in the column. The particle size was found to decrease with increasing axial height. Voidage increased with axial height from a settled bed value of 0.39 to approaching unity for high liquid velocities and increased at a constant axial position with increased flowrate. This information provides key insight into bed stability and data for the improved modeling of this important unit operation.
