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To investigate the interplay between particle charging and hydrodynamics in fluidized beds, models for triboelectric charging and electrostatic forces were built into a CFD-DEM model. Charge transfer was governed by the difference in effective work function between contacting materials as well as the electric field at the point of contact. Monodisperse particles were fluidized with an effective work function difference between the particles and the conducting walls. For smaller work function differences, hydrodynamics were not changed significantly as compared to an uncharged case. In these simulations, the average charge saturated at a value much lower than the value anticipated based on the work function difference, and a unimodal distribution of charges was observed. For larger work function differences, particles stuck to walls and bed height oscillations due to slugging were less pronounced. For these cases, a bimodal distribution of charges emerged due to effects from strong electric fields. This article is protected by copyright. All rights reserved.

The behavior of SiO 2 nanoparticles and the effects of operating conditions on nanoparticle agglomerate sizes have been investigated under conditions created in a vibro-fluidized bed (VFB). The experimental results reveal that the vibrations imposed in the bed can suppress slugging and/or channeling, in contrast to conventional fluidization with upflow only. The vibrations imposed in the particle bed affect both the minimum fluidization velocity and the agglomerate size, both of which decrease with increases in the energy introduced to the bed by the vibrations. The effect of vibrations on the agglomeration in vibro-fluidized beds of nanoparticles depends on the critical vibration frequency corresponding to a minimum agglomerate size. Both the amplitude and the frequency of the applied vibrations have significant effects on the agglomerate size. The experimental results and the consequent analysis reveal that increasing levels of vibrations in the bed yields finer agglomerates. The Richardson-Zaki scaling law combined with Stokes law permits the prediction of agglomerate sizes and the extent of initial bed voidage. The average agglomerate sizes predicted are in good agreement with those determined experimentally.

A novel biomass, autothermal, fast pyrolysis reactor with a draft tube and an internal dipleg dividing the reactor into two interconnected beds is proposed. This internally interconnected fluidized beds (IIFB) reactor is designed to produce high-quality bio-oil using catalysts. Meanwhile, the pyrolysis by-products, i.e., char, coke and non-condensable gases, are expected to burn in the combustion bed to provide the heat for the pyrolysis. On the other hand, the catalysts can be regenerated simultaneously. In this study, experiments on the hydrodynamics of a cold model IIFB reactor are reported. Geldart group B and D sand particles were used as the bed materials. The effects of spouting and fluidizing gas velocities, particle size, static bed height and the total pressure loss coefficient of the pyrolysis bed exit, on the flow patterns and pressure drops of the two interconnected beds are studied. Six distinct flow patterns, i.e., fixed bed (F), periodic spouted/ bubbling bed (PS/B), spouted bed with aeration (SA), spout-fluidized bed (SF), spout-fluidized bed with slugging (SFS) and spouted bed with backward jet (SBJ) are identified. The investigations on the pressure drops of the two beds show that both of them are seen to increase at first (mainly in the F flow pattern), then to decrease (mainly in the PS/B and SA flow patterns) and finally to increase again (mainly in the SA and SF flow patterns), with the increase of the spouting gas velocity. It is observed that a larger particle size and lower static bed height lead to lower pressure drops of the two beds.

Spouting of 3.7 mm polyvinyl chloride particles in a cone-based cylindrical column is subjected to entrainment of FCC powder in the spouting air. It is found that the powder entrainment reduces the minimum spouting velocity, increases the bed pressure drop and reduces the maximum spoutable bed height. At any given bed height and value of U/Ums, there is a critical value of powder loading ratio above which spouting gives way to slugging. Le jaillissement de particules de chlorure de polyvinyle dans une colonne cylindrique a base conique a ete soumis a un entrainement de poudre de FCC dans l'air jaillissant. On a trouve que l'entrainement de poudre reduisait la vitesse de jaillissement minimale, augmentait la perte de charge de lit et reduisait la hauteur maximum de lit jaillissant. A toute hauteur de lit et valeur de U/Ums donnees, il existe une valeur critique du rapport de charge de poudre au-dessus duquel le jaillissement conduit au pistonnage.

Drying of nylon (Geldart D) and expanded polystyrene (Geldart B) particles in fixed and fluidized beds were studied experimentally and theoretically. Fluidized bed dryers are sometimes operated at velocities beyond bubbling fluidization to mitigate against de-fluidization of surface wet particles. It was found that theoretical analysis using three different drying methods could predict the constant-drying rate at such velocities and also across the entire fluidization regimes (fixed bed, bubbling, slugging and turbulent fluidization) as long as the bed remains completely fluidized. Results also showed that the theoretical predictions were accurate beyond previously reported velocity limits in a laboratory scale dryer. During bubbling fluidization, the cross flow factor method was used effectively to predict the influence of bubble phase on drying rates. In the falling-rate period, it is demonstrated that the drying behaviour of nylon at different gas velocities can be characterised by a single normalized drying curve.

An experimental investigation was conducted of slot-rectangular spouted beds with air entry slots spanning the full thickness of the column and vertical draft plates intended to help control the solids circulation rate. With increasing superficial gas velocity, the flow between the draft plates changed from bubbling to slugging and then to spouting with dilute pneumatic between the plates and moving-bed downward motion on both sides. However, there was difficulty maintaining stability and symmetrical flow on the two sides. Once spouting is established, pressure drops and local voidages vary with gas velocity, particle size and gas entry size in broadly similar manners as for conventional spouted beds.

Hydrodynamic studies were conducted in a semi-cylindrical spouted bed column of diameter 150 mm, height 1000 mm, conical base included angle of 60° and inlet orifice diameter 25 mm. Pressure transducers at several axial positions were used to obtain pressure fluctuation time series with 1.2 and 2.4 mm glass beads at U/Ums from 0.3 to 1.6, and static bed depths from 150 to 600 mm. The conditions covered several flow regimes (fixed bed, incipient spouting, stable spouting, pulsating spouting, slugging, bubble spouting and fluidization). Images of the system dynamics were also acquired through the transparent walls with a digital camera. The data were analyzed via statistical, mutual information theory, spectral and Hurst's Rescaled Range methods to assess the potential of these methods to characterize the spouting quality. The results indicate that these methods have potential for monitoring spouted bed operation. Des etudes hydrodynamiques ont ete menees dans une colonne a lit jaillissant semi cylindrique de 150 mm de diametre, de 1000 mm de hauteur, ayant un angle d'ouverture de la base conique de 60° et d'un diametre d'orifice interieur de 25 mm. On a employe des capteurs de pression a differentes positions axiales dans le but d'obtenir des series temporelles de fluctuation de pression, avec des billes de verre de 1,2 et 2,4 mm, a U/Ums de 0,3 a 1,6 et des profondeurs de lit statique de 150 a 600 mm. Les conditions couvrent plusieurs regimes d'ecoulement (lit fixe, jaillissement naissant, jaillissement stable, jaillissement pulsatoire, pistonage, jaillissement a bulles et fluidisation). Des images de la dynamique des systemes ont egalement ete obtenues a travers des parois transparentes avec un appareil photo numerique. Les donnees ont ete analysees au moyen de diverses methodes (methodes statistiques, theorie des informations mutuelles, methodes spectrales, methode a amplitude renormalisee de Hurst) afin d'evaluer le potentiel de ces methodes pour caracteriser la qualite du jaillissement. Les resultats indiquent que ces methodes sont potentiellement interessantes pour la surveillance du fonctionnement en lit jaillissant.

The fluidization characteristics of anthraquinone hydrogenation catalysts were investigated in a liquid-solid fluidized bed. The effects of the initial bed conditions such as particle size, bed depth-to-column diameter ratio and liquid density and viscosity on the fluidization behaviour, bed expansion and applicability of the Richardson - Zaki equation were studied. The results reveal a strong particle size effect on the Richardson - Zaki (R-Z) expansion index which in general decreased as the particle diameter increased. One type of particles exhibited two distinct bed expansion behaviours, depending mainly on the bed depth-to-column diameter ratio, with an experimentally established boundary at h(b0)/D approximate to 1.75. This behaviour could be attributed to increasing wall friction and a tendency to exhibit slugging. The dependence of the Richardson - Zaki exponent on the liquid dynamic viscosity confirms the classic result n(a) = f(1/Re(t)).

Fluidization conditions in a circulating-fluidized bed (CFB) can vary dramatically, from bubbling to circulating regimes. The granular Eurlerian models have been used to simulate the bubbling and slugging behavior of gas and solids in CFB. Considering the dielectric properties and rapid movement of solids in CFB, electrical capacitance tomography (ECT) is particularly suitable for measuring the concentration and distribution of solids in CFB to verify the simulation results. The simulation results by computational fluid dynamics (CFD) analysis and experimental results obtained by ECT are reported, and compares the simulation and experimental results first time, including the solids concentration profile, temporal variation of average-solids concentration, autocorrelation coefficient and frequency spectrum. © 2006 American Institute of Chemical Engineers AIChE J, 2006

The fluidization behaviors of various nanometer and micron particles, including SiO 2 , TiO 2 , and cornstarch particles with primary particle sizes of 5 nm-10.69 μm, were investigated in a fluidized bed with inside diameter 56 mm under different sound pressure levels and sound frequencies. It has been demonstrated that the relatively uniform ultrafine particle agglomerates reach homogeneous fluidization with sound assistance at low sound frequencies due to the sound field disrupting large size agglomerates. Furthermore, slugging and channeling of the bed was eliminated, accompanied by negligible elutriation. For each of the nanometer and micron particles examined, the minimum fluidization velocity decreased with increasing sound frequency, and then increased with sound frequency at a given sound pressure level. There is a minimum value in the curve of minimum fluidization velocity versus sound frequency, the critical sound frequency, at which the bed fluidized smoothly. Varying the sound pressure level can significantly improve the fluidization quality of the bed.

Some experimental observations on the fluidization characteristics of nanoparticles in the form of agglomerates with magnetic assistance are presented. The nanoagglomerates consist of Degussa Aerosil® R974 fumed silica, with a primary particle size of 12 nm. An oscillating AC magnetic field is used to excite large (mm size) permanent magnetic particles mixed in with the nanoparticle agglomerates, and the fluidization behavior of the nanoagglomerates, including the fluidization regime, the minimum fluidization velocity, the bed pressure drop, and the bed expansion are investigated. It is shown that, with the aid of an oscillating magnetic field at low frequencies, the bed of nanoparticle agglomerates can be smoothly fluidized, and the minimum fluidization velocity is significantly reduced. In addition, channeling or slugging of the bed disappears and the bed expands uniformly without bubbles, and with negligible elutriation. The bed expansion and the minimum fluidization velocity depend on the mass ratio of magnetic particles to nanoparticles, and the intensity and frequency of the oscillating magnetic field. © 2005 American Institute of Chemical Engineers AIChE J, 2005

An experimental study of heat transfer into gas-fluidized beds has been carried out with heat transfer into discriminated areas of the boundary walls, and into single and multiple elements immersed in the bed. The experiments have been carried out with glass ballotini ranging in size from 100 μm to 1 mm in diameter, on Diakon (Perspex) particles of 325 μm, and on nickel particles of 275 μm and 325 μm covering a range of Archimedes numbers from 100 to 100000. Beds of different diameter with distributors of several different types have been examined. The entire experimental results have been compared with literature data on heat transfer to immersed elements. It is shown that the onset of slugging in the fluidized bed has a large effect on heat transfer. Once the effect of slugging has been introduced, it is shown that the results of this investigation and others in the literature within the range of Archimedes numbers from 100 to 10 9 may be correlated.

A two-phase structural model consisting of a dense phase and a dilute phase with allowance for the dense-phase expansion and the solids holdup in the dilute phase was developed and successfully applied to the analysis of local voidage fluctuation signals. Such a model can be used to derive local-phase holdups and voidage in each phase in both bubbling/slugging/turbulent fluidized beds and circulating fluidized-bed risers without ambiguity in defining criteria for dividing phases used by previous researchers. Such a model can also explain the existence of a maximum standard deviation at a local voidage around 0.7, and why a maximum peak is observed in the radial profiles of standard deviation of local voidage fluctuations in high-velocity fluidized-bed columns.

In fully developed slugging fluidized beds, the maximum amplitude of absolute pressure fluctuations is reached with increasing superficial gas velocity when the slug length reaches a maximum, and the separation distance between successive slugs starts to decrease. Uc, the superficial gas velocity at which absolute pressure fluctuations reach a maximum, thus indicates the early stage of transition from slugging to core-annular flow. Uc, identified based on standard deviations of differential pressure fluctuations or local voidage fluctuations, can be predicted by slug flow models and does not signify a transition to turbulent fluidization. Dans les lits fluidises bouchonnants pleinement developpes, l'amplitude maximale des fluctuations de pression absolues est atteinte avec l'augmentation de la vitesse de gaz lorsque la longueur du bouchon atteint un maximum, et quand la distance de separation entre les bouchons successifs commence a diminuer. Uc, la vitesse de gaz superficielle a laquelle les fluctuations de pression absolues atteignent un maximum, indique ainsi le tout premier stade de transition entre l'ecoulement bouchonnant et l'ecoulement coeur-espace annulaire. Uc, determine d'apres les ecarts types de fluctuations de pression differentielle ou de fluctuations de vide locales, peut etre predit par des modeles d'ecoulement piston et ne signifie pas une transition a la fluidisation turbulente.

Pressure fluctuations within a bed of Type D particles (coarse sand, long grain rice, red spring wheat, 10 mm glass beads, pearl barley and whole peas) were measured at various bed heights. Analysis of the pressure fluctuation profiles leads to correlations that predict the minimum slugging velocity and slugging frequency, within experimental ranges. Results reveal that past correlations have little success in predicting the slugging characteristics for large particles. Particle shape plays an important role on the type of slug formed and therefore on the values of slugging frequency and minimum slugging velocity. Large particles with low sphericity formed wall slugs with high slugging frequencies and required the greatest amount of excess air to achieve slugging. On a mesure a des hauteurs de lits differentes les fluctuations de pression dans un lit garni de particules de type D (sable grossier, riz a grains longs, ble de printemps rouge, billes de verre de 10 mm, orge perle et pois entiers). L'analyse des profils de fluctuation des pressions a conduit a des correlations qui predisent la vitesse de bouillonnage minimum et la frequence du bouillonnage, dans les gammes experimentales. Les resultats revelent que les correlations passees reussissent mal a predire les caracteristiques de bouillonnage pour les grosses particules. La forme des particules joue un rǒle important sur le type de bouchon forme et donc sur les valeurs de frequence du bouillonnage et la vitesse de bouillonnage minimum. Les grosses particules ayant une petite sphericite forment des bouchons aux parois avec des frequences de bouillonnage elevees, et elles necessitent le plus grand exces d'air pour realiser le bouillonnage.

The recognition of flow regimes is very important in the application of spouted beds. In this paper, two-dimensional computer simulations of a slot-rectangular spouted bed using FLUENT commercial software were utilised to construct flow regime maps. Two-phase gas–solid flows in the bed were simulated with computational fluid dynamics (CFD) using the two-phase Eulerian–Eulerian granular model. The numerical simulations were applied to predict different flow regimes. The constructed flow regime map for a bed containing solid particles with a diameter of 1.44 mm was in good agreement with the experimental map previously reported elsewhere. With this successful numerical mapping, a flow regime map for particles with a diameter of 3.77 mm was constructed for various superficial gas velocities and static bed heights. The map was composed of six distinct flow patterns, that is fixed bed, internal jet, jet-in-fluidised-bed, spouting, incoherent spouting and slugging. The slugging flow regime occurred at large values for the static bed height and air inlet velocity, while the spouting regime arose by increasing the air inlet velocity at low values of static bed height. Unlike the spouting regime, large pressure drop fluctuations were observed in the incoherent spouting regime.

Hydrodynamics of a powder-particle spouted bed (PPSB) with bottom feeding of fine powders conveyed by spouting gas has been investigated. Feeding of fine powders caused an increase in bed pressure drop, especially when a cohesive powder was fed. The minimum spouting velocity decreased with increasing feed rate of fines until a critical value, above which slugging occurred. Also, the fines became difficult to elutriate out of the PPSB when using a cohesive powder smaller than 40 µm. The elutriation rate constant and the mean residence time of fines in this study almost agreed with those obtained by top feeding.

This paper describes the use of a capacitance tomography system for imaging gas bubbles in a fluidized bed in the vicinity of an air distributor plate. The results show how the solid concentration distribution varies as a function of time for three different flow regimes: bubbling, slugging and the transition to turbulent. Bubble shape, length and coalescence can be observed. A method of spatial correlation to elucidate the bubble formation process is described.

Rosensweig's (1979) analysis of the stability of gas-fluidized magnetically stabilized fluidized beds (MSFBs) with voidage perturbations is modified to include terms dependent on the fluid density. This allows the stability analysis to be applicable to liquid-fluidized MSFBs, which have potential use in liquid chromatography. Results show that in systems where the fluid density is not insignificant when compared to the solid-phase density, the difference in density between the two phases should be used when normalizing the magnetization required to achieve stability. Comparisons between theory and experiment show that although the present analysis improves on Rosensweig's analysis, it still does not give reliable, quantitative predictions of stability behavior. It is suggested that for liquid-fluidized MSFBs, stability to particle velocity perturbations, rather than to voidage perturbations, is more relevant to chromatographic applications wherein the purpose of magnetic stabilization is to prevent particle mixing as opposed to preventing the occurrence of bubbling and slugging observed in gas-fluidized beds.

Gas mixing in a tall narrow fluidized bed operated in the slugging fluidization regime is simulated with the aid of computational fluid dynamics. In the first part, a parametric study is conducted to investigate the influence of various parameters on the gas mixing. Among the parameters studied, the specularity coefficient for the partial-slip solid-phase wall boundary condition had the most significant effect on gas mixing. It was found that the solid-phase wall boundary condition needs to be specified with great care when gas mixing is modeled, with free slip, partial slip and no-slip wall boundary conditions giving substantial differences in the extent of gas back mixing. Axial and radial tracer concentration profiles for different operating conditions are generally in good agreement with experimental data from the literature. Detailed analyses of tracer back mixing are carried out in the second part. Two parameters, the tracer backflow fraction and overall gas backflow fraction, in addition to axial profiles of cross-sectional averaged tracer concentrations, are evaluated for different flow conditions. Qualitative trends are consistent with reported experimental findings. © 2010 American Institute of Chemical Engineers AIChE J, 2010

The effect of particle size distribution (PSD) on the performance of a fluidized bed reactor was investigated in different hydrodynamic regimes: bubbling, slugging, turbulent and fast fluidization, with three particle size distributions, all with the same mean diameter and nearly the same particle density and BET surface area. Regime transitions were examined by measuring pressure fluctuations. Void sizes tended to be smaller and the transition from bubbling or slugging to turbulent fluidization was achieved earlier for the wide distribution powder than for the narrow PSD. At gas velocities ≤ 0.2 m/s, the conversion and reactor efficiency were not affected greatly by the PSD. However, at higher gas velocities, PSD played a significant role. For particles of wide size distribution, the conversion in the turbulent and fast fluidization regimes was usually higher than in the bubbling fluidization regime at the same dimensionless rate constant, kf′. On the other hand, for particles of narrow size distribution, the dependence of conversion on the regime is small, except for the fast fluidization regime.

Etude experimentale de l'influence de la dimension des particules et de la vitesse relative du gaz sur la frequence dominante et l'amplitude moyenne de pression

Solid tracer particles were fed pneumatically through a jet into a fluidized bed to simulate the feeding of solids via a pneumatic transport line into a fluidized-bed reactor operating in the slugging-bed mode. The fluidized bed was defluidized instantaneously at different times after the initiation of the tracer particle injection. The bed was then sampled layer by layer to provide the radial and axial concentration profiles of the tracer. Regular and high-speed movies (1,000 frames per second) were taken to study the operation of the fluidized bed and the phenomena of the gas-solid two-phase jet. Experimental results on solid mixing, jet constriction and slugging frequencies, slugging bed height, slug length, jet penetration, and jet half-angle at three nominal jet velocities of 52, 37, and 25 m/s and corresponding solids loadings are presented. Additional experimental results on jet constriction and slugging frequencies, and slug volume (axial slug size) obtained for a wider range of jet velocities confirm the hydrodynamic trends observed during the tracer particle injection experiments. The results indicate that solids mixing increases, and well-mixed conditions are reached earlier, with an increase in jet injection velocity. The obtained mixing times were correlated successfully in terms of the excess gas velocity. The experimental data on jet penetration and slug motion were satisfactorily correlated by modified versions of existing theoretical relations. The modifications included the effect of the injected solids on jet penetration and jet half-angle and also the effect of our semicircular column geometry and single wall-slug configuration on the observed slug motion.

Slugging characteristics, including slug velocity and frequency and the height of the slugging bed, for a slugging bed of four different types of coarse particles ranging from 1 to 7 mm in size are determined based on pressure fluctuation behavior of the bed. The slugging characteristics of coarse particle slugging beds are found to be much different from those of the particle slugging beds reported in the literature. The pressure fluctuation behavior in a coarse particle turbulent bed and the transition velocity from a slugging bed to a turbulent bed is also examined.

A model is developed for slugging fluidized bed catalytic reaction which improves on the model of Hovmand and Davidson by incorporating the solids mixing. The model parallels the countercurrent backmixing model of Fryer and Potter. Solids mixing is accounted for by the model of Thiel and Potter which assumes the rising slug is followed by a well-mixed wake into and out of which solids flow at a rate determined by the rise velocity of the slug. Comparison is made with experimental data reported by Hovmand and Davidson with good results.

A comprehensive investigation has been made of the boundaries of the regime of bubbling aggregative fluidization. Experiments were done with sand, glass beads, clover seed, and iron shot fluidized with helium, air, and freon-12 in columns 2.5, 5, 10, and 21 cm in diameter. Bed heights ranged from 1 to 60 column diameters, particle diameters from 0.07 to 1.1 mm, particle densities from 1300 to 7600 kg/m3, and gas densities from 0.17 to 5.2 kg/m3. Correlations are presented for the void fraction at the minimum bubbling point and for the superficial fluid velocity at the points of minimum fluidization, minimum bubbling, and minimum slugging.

Models are presented for determining flow regime transitions in two-phase gas-liquid flow. The mechanisms for transition are based on physical concepts and are fully predictive in that no flow regime transitions are used in their development. A generalized flow regime map based on this theory is presented.

Slugging experiments were performed in a semicircular Plexiglas column 5.6 m in height to study the effect of an expanded section on slugging. The bottom section of the column (3.05 m long) is 28.6 cm in inside diameter and the expanded section 40.6 cm. Both the bed height and the fluidizing velocity were varied during the study, and the results were successfully correlated with a theoretically derived equation. The implications in designing a bed with an expanded section to reduce the slugging effectively are also discussed.

A mechanism is proposed suggesting that the wavy-slug transition during horizontal condensation is initiated by a hydraulic jump. Based on this mechanism, a simple empirical correlation is developed and shown to be consistent in magnitude and trend with data for different fluids and different tube diameters. Further, a theoretical model is constructed for stratified two-phase flow near the end of the condensation path utilizing the principles of mass, momentum and energy conservation. Results from the model together with the proposed slugging mechanism succeeded in defining a theoretical wavy-slug transition line which agrees well with experimental flow regime data for a wide range of operating conditions. On propose un mecanisme qui suggere que la transition entre les ecoulements ondule et saccade au cours de la condensation horizontale, est initiee par une discontinuite hydraulique. Une correlation simple a ete developpee a partir de ce mecanisme, dont les resultats se sont averes coherents avec les donnees pour differents fluides et diametres de tubes. En outre, on a etabli un modele theorique pour l'ecoulement biphasique stratifie obtenu a la fin de la condensation, en utilisant les principes de conservation de matiere, de quantite de mouvement et d'energie. Les resultats du modele ainsi que le mecanisme propose pour la formation des bouchons ont permis de definir une ligne theorique de transition, qui est en bon accord avec les donnees experimentales de regime d'ecoulement pour une large gamme de conditions operatoires.

This study investigated solids mixing of a group A fine powder in a 0.15 m ID expanded top fluid bed with a ferromagnetic tracer. The superficial gas velocity was raised from 0.075 to 1.1 m/s, causing the bed to go through bubbling, slugging, and turbulent fluidization regimes. A countercurrent flow model described the data well at low gas velocities. The bed assumed a more homogeneous appearance at higher gas velocities; a one-dimensional axial dispersion model was used to correlate the data. Axial dispersion coefficients increased with gas velocity. The data agree well with literature data for low gas velocities.

A study has been made of the effect of fixed packing on the properties of a gas-fluidized bed, including minimum fluidization velocity, pressure drop, and bed expansion. Experiments using a range of glass beads as fluidizing solid with smooth uniform spheres as packing indicate that both packing size and the ratio of particle to packing diameter are the main variables in correlating the results. Other solids of varying density and shape have also been used. In addition to smooth spherical packing, rough spheres and variously shaped packings such as Raschig rings, Berl saddles, and a cylindrical, open-ended screen packing have received preliminary study. With the screen packing, which occupies only 5% of the column volume, it has been possible to operate a fluidized bed at a much higher gas throughput without slugging than is possible with a conventional bed. A preliminary study has also been made of heat transfer rates, and the results indicate that the same factors are significant. With spherical packing, values of h of the order of 70% of that in a conventional bed have been obtained, while with screen packing values ranging up to 100% or greater have been observed. Possible applications of this technique and its limitations are also discussed.

A study has been made of the expansion characteristics of beds of uniformly sized spherical particles of lead, nickel, sand, glass, and plastic that have been fluidized with air, carbon dioxide, and helium in columns packed with open-ended cylindrical screen packing. The addition of packing to a gas-fluidized bed limits the bubble size, prevents slugging and allows beds of high aspect ratio to expand smoothly in a manner similar to the behavior of liquid-fluidized beds. Moreover, much of the experimental data for gas-fluidized screen-packed beds have yielded straight lines on a Richardson-Zaki type of plot, again similar to the expansion of liquid-fluidized beds. The conditions necessary for this pseudoparticulate behavior in packed gas-fluidized beds are discussed. A correlation, based on the analysis given by Richardson and Zaki for liquid-fluidized beds, is proposed to relate bed porosity with gas velocity, density and viscosity, particle size and density, and bed diameter. (Author)

Slug flow in the air-water system near atmospheric pressure was studied in a one-half inch diameter tube. Measurements of flow characteristics, pressure gradient, pressure fluctuations, slug velocity and frequency were made for horizontal and inclined flow. A semi-empirical theory based on a simple model was developed. Pressure losses calculated from this theory require a priori knowledge of the slugging frequency. A comparison of the prediction of the theory and two published correlations shows that the proposed theory gives better agreement with the data.

The results of some studies on the effect of (1) ball-milling time, (2) granulating by “slugging,” and (3) dry pressing of pure oxide ceramic bodies are presented. When the compressive strength of specimens of single-component bodies was plotted against ball-milling time (in revolutions), minima in the curves were found between 30,000 and 50,000 revolutions. For a multicomponent body of the porcelain type and one of the oxide porcelain type, when the same data were plotted, maxima in the curves were found between 30,000 and 40,000 revolutions. Granulating by slugging provided 30% greater compressive strength, 1.5% less shrinkage, and 1% less absorption in the specimens as compared with specimens formed from ungranulated material. High-pressure forming, preferably by hydrostatic pressure, was desirable; however, there appeared to be an optimum pressure for the physical properties of each material.