Fluidization Patterns Research Articles

Characterization of Particle Fluidization Pattern in a Gas Solid Fluidized Bed Based on Acoustic Emission (AE) Measurement

Flow pattern of the fluidized bed is a key factor for heat transfer and the design of a new reactor. It is important to comprehend the fluidization conditions because the complex correlation between particle−particle and particle−environment in the reactor. In this study, we applied acoustic emission (AE) measurement in monitoring the particle fluidization pattern in a gas−solid bed fluidized with different sorts of particles classified by Geldart. With AE axial time average energy analysis, the flow structure of polyethylene particles was investigated both in the laboratory and plant apparatus. The results showed that the fluidization pattern in the bed is multicirculation, including the main-circulation zone, subcirculation zone, and the stagnant zone. Moreover, the influence of operating variables, such as particle size, superficial gas velocity, static bed height, and particle sorts had also been considered. It was found that the particle size, gas velocity, and particle sorts have significant impacts to the fluidization pattern. In contrast, the height of the stagnant zone did not show direct relation to the static bed height. AE measurement was proved to be reliable for understanding the dynamical features that affect the behavior of the fluidized bed. This can be useful guidance for an industrial process and help improve the process operation and the design of the new reactor.

Application of Hot-Melt Coating Process for Designing a Lipid Based Controlled Release Drug Delivery System for Highly Aqueous Soluble Drugs

Hot-melt coating process (HMCP) was applied to develop a lipid based oral controlled release matrix system (tablet) to deliver highly aqueous soluble drugs using paracetamol as a model drug. Granules prepared from paracetamol and particular filler were coated with different levels of lipid and then compressed into tablets to get controlled/sustained delivery of the drug over an optimum period. Process parameters were optimized with particular focus on fluidization pattern during HMCP proposing a 'design space' with 'Quality by Design' (QbD) concept in mind. The results demonstrated that the granule composition influenced the drug release pattern, and the rate of release could be manipulated by varying the amount of lipid in the formulation. The in vitro release profile of the drug was pH-independent and the most promising release profile was obtained from tablets prepared from granules with the water-soluble filler, lactose, and coated at 9% (w/w) level with a lipid, glyceryl behanate. In vivo plasma profiles of the drug were predicted from the in vitro release profile data by convolution analysis which confirmed that the lactose based formulation with 9% (w/w) lipid coating on the granules would be suitable for controlled delivery of the drug over a period of 12 h making the formulation suitable for highly water soluble drug candidates like paracetamol with twice daily dose regimen. Moreover, the dissolution data adequately fitted into Higuchi model suggesting that the drug release occurred predominantly by diffusion.

The fluidization pattern of density-segregating binary mixtures

This paper analyses the process of fluidization of mixtures of two spherical solids differing only in density and addresses the relationship between bed suspension and component segregation. It is shown that relating the progress of segregation to the excess gas velocity u– u mf, a parameter that should represent the intensity of bubbling, gives way to serious errors, due to the fact that extending to binary beds the concept of minimum fluidization velocity leads to overlook some important aspects of their behaviour. A clearer description of the fluidization properties of density-segregating mixtures is that based on the definition of the ‘initial’ and ‘final fluidization velocity’ of the binary bed. Such an alternative approach provides an effective representation of the actual behaviour of these systems, as it correctly accounts for all the variables which affect their phenomenology of fluidization.

Theoretical and experimental study on hydrodynamic characteristics of fluidization in air–sand conical beds

This work was aimed at modeling hydrodynamic characteristics of fluidization in conical beds using quartz sand as the inert bed material and air as the fluidizing agent. The minimum fluidization velocity, u mf , and the minimum velocity of full fluidization, u mff , were determined by Peng and Fan's models modified for conical fluidized bed. Meanwhile, the pressure drop across a bed, Δ p (including Δ p max and Δ p mff corresponding to u mf and u mff , respectively), was predicted by using modified Ergun's equations for variable superficial air velocity at an air distributor, u 0 . The predicted results were validated by experimental data for some operating conditions. Effects of the sand particle size, cone angle and static bed height on the fluidization pattern and hydrodynamic characteristics are discussed. With the proposed models, the Δ p – u 0 diagram were obtained with rather high accuracy for the conical air–sand beds of 30– 45 ∘ cone angles and 20–30 cm static bed heights, when using 300– 1180 μ m sand particles. For the predicted u mf and u mff , the relative computational errors were found to be within 20% for wide ranges of operating variables, whereas Δ p max and Δ p mff could be predicted with lower (10–15%) relative errors. With higher cone angles and/or bed heights, the computational accuracy was found to deteriorate.

Experimental and Numerical Study of Rotating Fluidized Beds in a Static Geometry

The new concept of a rotating fluidized bed in a static geometry was numerically and experimentally studied. The particle bed can be both tangentially and radially fluidized by injecting the fluidization gas tangentially in the static fluidization chamber via multiple gas inlet slots located in its outer cylindrical wall. The tangential fluidization of the particles induces a rotating motion of the particle bed. As a result of the particle bed rotational motion, the solids experience a radially outwards centrifugal force. A radially inwards gas-solid drag force and radial fluidization of the particle bed can be introduced by forcing the fluidization gas to leave the fluidization chamber via a chimney with one or multiple gas outlet slots, positioned at the axis of the fluidization chamber. The solids can be continuously fed and removed in and out of the fluidization chamber via solids inlet and outlet holes in the front or back ends of the fluidization chamber.The fluidization patterns of low-density polymer particles with a large diameter and of high-density salt particles with a small diameter were experimentally studied in a 24-cm diameter, 13.5-cm long non-optimized static fluidization chamber at different solids loadings. Scale-up to a 36-cm diameter fluidization chamber was also studied. With both types of particles, a rotating fluidized bed and an acceptable gas-solid separation was obtained provided that the solids loading was sufficiently high. Slugging and channeling and a non-uniform distribution of the gas over the gas inlet slots to the fluidization chamber may occur at low solids loadings and can be detected via well-chosen pressure measurements. The fluidization patterns observed in the same fluidization chamber were completely different with the polymer particles and with the salt particles. The polymer particles tend to form a dense and uniform bed, its behavior being mainly characterized by tangential fluidization. The salt particles tend to form a less dense, bubbling fluidized bed that is both tangentially and radially fluidized.Computational fluid dynamics simulations give an improved insight in the gas and solid phase flow pattern.

Morphology and geometry of Valles Marineris landslides

The walls of the Valles Marineris canyons are affected by about 45 landslides. The study of these landslides provides a test of the hypothesis of processes having affected Martian wallslopes after their formation. The dynamics of Valles Marineris landslides are controversial : either the landslides are interpreted as large debris flows or as dry rock avalanches. Their morphology and their topography are basic parameters to understand their dynamics. From topographic MOLA data and remote sensing images acquired with different spatial resolutions (Viking, THEMIS, MOC), the 3D geometry of 45 landslides of Valles Marineris has been studied. The landslides have been classified in 3 geomorphologic classes from the topography of the landslide deposits: the “chaotic” landslides without well identified structures, the “structured deposit without debris aprons” landslides with tectonic structures and small roughness at the deposit front and the “structured deposit with debris aprons” which display circular normal faults at the back of the deposit and several debris aprons at the front of the landslide. The spatial distribution of the three morphological types is in relation with the confinement of the canyons. The initial volume and the total deposited volume were also measured to compute volume balances. The deposited volumes range from 50 to 5000 km 3 . All volume balances display a maximum deficit ranging from 5% to 70%. The landslides with the largest deficits take place within an enclosed-canyon (Hebes Chasma). Lacking material exportation, these deficits could be interpreted as reflecting the porosity of the landslide source. This fact is in agreement with the hypothesis of a karstic origin of these enclosed-canyons. The Valles Marineris landslides have large mobilities (length/vertical drop) ranging from 1.8 to 12 implying low coefficients of friction and so fluidization mechanisms. The possible filling up of the porosity by volatile could be compatible with the fluidization patterns of Valles Marineris landslides.

Factors affecting differences in film thickness of beads coated in fluidized bed units

Previous work (Wesdyk et al., Int. J. Pharm., 65 (1990) 69–76) demonstrated that various size beads, dispersed in a single bed, display differences in film thickness when coated in a fluidized bed apparatus equipped with a Wurster column. The differences in film thickness were attributed to differences in fluidization patterns and velocities of the various size beads. The present study examines the effect of spray mode and process parameters on the variation of film thickness for a fixed particle size range and distribution. Beads with a size distribution in the no. 14-no. 20 mesh range were coated with an aqueous polymeric dispersion using top, bottom, and tangential spray fluidized bed units. Film thickness of the coated beads was measured using a scanning electron microscopic method. It was observed that unlike batches coated in the bottom spray (Wurster) mode, the batches coated in the top and tangential spray modes exhibited no trend in film thickness. These results are consistent with the differences observed in the surface area normalized release rates of the various size beads coated in the three spray modes. The results also indicated that for the bottom spray mode, a reduction in the atomizing air pressure, while substantially reducing differences in fluidization patterns, had only a marginal effect in reducing the differences in film thickness.

The effect of size and mass on the film thickness of beads coated in fluidized bed equipment

The relationship between the film thickness on a bead, and the bead's size and mass in a polydispersed system was studied. Beads with a size distribution in the no. 14–20 mesh range were coated using Glatt fluidized bed units equipped with a Wurster insert. The coated beads were separated into narrower size fractions and dissolution testing of each fraction was performed using the USP basket method. The larger beads exhibited much slower release rates compared to the smaller beads, and the differences could not be explained by the relative surface areas. Examination of the beads by scanning electron microscope indicated that the larger or heavier beads received a thicker film compared to the smaller or lighter beads. This trend was attributed to differences in the fluidization patterns and velocities of the various sized beads.

A fundamental study of fluidization and heat transfer characteristics arond a horizontal heated circular cylinder immersed in a fluidized bed.

The fluidization and heat transfer chracteristics around a single horizontal heated circular cylinder immersed in a fluidized bed are fundamentally studied in this paper to elucidate the mechanism of heat transfer augmentation in a fluidized bed heat exchanger. The state of fluidization of p. articles is observed for various fluidization velocities covering fixed and fluidized beds. Further-more, the fluctuating pressure and the local heat transfer coefficient around the cylinder are measured. The fluidization patterns of the bed of the fixed, bubbling, slugging and turbulent states correspond to the fluctuating pressure around the cylinder. The local behavior of p. articles near the cylinder surface are classified into three categories : (1) the still region, ( 2 ) the sliding region and ( 3 ) the mixing region. The position where the maximum local heat transfer coefficient takes p. lace is located nearly on the boundary between the sliding and mixing regions and moves toward the rear side along with the boundary with an increase of fluidization velocity.