Bed Expansion Behavior Research Articles

Hydrodynamic and Heat Transfer Characteristics of an Air Fluidized Bed Utilizing a Transverse Magnetic Field

The effect of transverse magnetic field on hydrodynamic and thermal behavior of a gas-solid bed of ferro-magnetic particles has been investigated. Phase diagrams, bed expansion behavior, wall-to-bed heat transfer coefficient and the temperature distribution in the radial direction under the effect of magnetic field and gas velocity have been determined in both magnetizing first and last modes of operation. The results indicate that the minimum fluidization velocity Umf, bed porosity (e), heat transfer coefficient (h) and the radial temperature distribution were strongly affected by both the gas superficial velocity and magnetic field intensity.

Modeling of Biological Particle Mixing in a Fluidized‐Bed Biofilm Reactor

Performance of fluidized‐bed biofilm reactors (FBBRs) greatly depends on the amount of biomass attached to the inert core support particles and overall bed voidage. Thus, for proper design of an FBBR, it is important to know the biological particle (bioparticle) mixing and bed expansion behavior, which in turn influence bed volume and consequently the residence time of the liquid phase. This paper first investigates the superiority of some of the predominantly used fluidization correlations for biological beds to predict bed voidage and, second, it investigates the implications of bioparticle mixing in FBBRs. The fluidization correlation suggested by Foscolo et al. (1983) was found to be superior to the more widely used Richardson and Zaki (1954) correlation to predict FBBR bed voidage. Furthermore, from the three different sets of published experimental results of bed voidage applied in this study, the fluidization correlation suggested by Foscolo et al. (1983), along with the terminal settling velocity equation suggested by Mulcahy and Shieh (1987), was found to be superior to other sets of correlations used in this study to predict bed voidage in an FBBR, having the lowest mean deviation of 12.7%. A mathematical model for fluidization of a binary bioparticle mixture is also presented in this paper to model the interaction of a variety of parameters, including upflow superficial liquid velocity, core support particle size and density, and biofilm thickness. Numerical simulations using this model revealed that, for sand‐like core support particles (density ranging from 1500 to 2700 kg/m 3), a complete segregation would likely occur in the bed with larger bioparticles at the top and smaller ones at the bottom. For charcoal‐ or polymer‐like core support particles (density ranging from 1050 to 1300 kg/m 3), a homogeneous bed made up of both larger and smaller bioparticles would likely occur. Comparison of the model predictions with published experimental results suggested excellent agreement.

Fluidization of potato starch in a stirred vibrating fluidized bed

A novel gas-solid reactor for cohesive C-powders such as potato starch is introduced, designed and characterized, the so-called stirred vibrating fluidized bed. The effects of a sinusoidal vibration of the gas distributor and/or stirring of the bed are investigated. The fluidization index, bed expansion, torque and visual behaviour of the bed are determined as a function of air velocity, bed height and moisture content of the starch, stirrer type and speed and vibration frequency and amplitude. For a potato starch bed of 0.76 m initial height and 0.288 m diameter with a moisture content W = 13.1 weight% dry basis, channel formation can be suppressed only if the aerated bed is effectively stirred. With flat stirrer blades this can be realized for stirring speeds above 1.67 rps provided the interblade distance is below 124 mm. Even then, the bed consists of agglomerates (flocks) of starch. Alternatively, vibration of the gas distributor of the aerated bed at best results in channel elimination in the lower part of the bed only. Sufficient vibration, however, can destroy starch agglomerates even at the surface of a bed of 0.76 m. By simultaneously applying both vibration and stirring of the aerated bed, it is possible to eliminate both channelling and starch agglomeration. Even homogeneous fluidization is possible. Optimal combinations of stirring and vibration parameters are reported for various bed heights and moisture contents.

High-performance liquid chromatography of amino acids, peptides and proteins: CXXIV. Physical characterisation of fluidized-bed behaviour of chromatographic packing materials

Bed expansion characteristics of several different chromatographic sorbent materials have been studied in liquid-solid fluidized bed systems with different column diameters. The sorbents used were sized below particle diameters ( d p) of 100 μm, and most were non-spherical in shape. The effect of particle shape and size distribution on the bed expansion behaviour and the values of bed expansion index were evaluated in relation to existing empirical correlations of bed voidage and fluid velocity under laminar flow conditions. The effect of fluid properties on the bed behaviour was studied using viscous bovine amniotic fluid as the feed stock. An axial dispersion model was used to compare the liquid mixing behaviour of the fluidized bed system with two different particle sizes of porous silica in 2.24 cm I.D. and 5.0 cm I.D. columns. The results on the bed expansion characteristics with these systems are discussed in terms of the dispersion coefficient, D x and the Peclet number N pe, for these sorbents fluidised under laminar flow conditions.

Liquid-fluidized magnetically stabilized beds

The fluid mechanics of liquid-fluidized magnetically stabilized beds (MSBs) have been studied to determine their operating characteristics and properties. Experiments were conducted to study the operating regimes, bed expansion and pressure drop, and axial liquid dispersion. Several regimes exist for magnetized, liquid-fluidized beds. These include the unfluidized or packed, stable, roll-cell, and random motion regimes. The transition between the stable and roll-cell regimes was found to be strongly dependent on the type of fluid distributor grid used. A hysteresis was found in both the pressure drop and bed expansion behavior. With decreasing liquid velocity, the pressure drop through the bed fell immediately to a value below the weight of the bed and the bed remained expanded even after the liquid flow had ceased. The height of the bed in the stable regime was found to depend on the liquid velocity but not on the strength of the magnetic field. Contacting experiments indicate axial dispersion in a liquid-fluidized MSB to be nearly the same as for packed beds and independent of the path taken to the stable operating condition.

Bed expansion characteristics of liquid fluidized particles with attached microbial growth

AbstractThe bed expansion behavior of liquid fluidized beds of char particles coated with attached microbial growth of denitrifying mixed bacteria was studied experimentally to obtain an expression that relates the bed expansion to the liquid velocity for liquid fluidized beds of composite particles. As for liquid beds of homogeneous spheres, the bed voidage and the liquid velocity vz for liquid fluidized beds of biomass‐coated particles were found to be related as vz/Vi = ∈n. The correlations recommended by Richardson and Zaki for homogeneous spheres are found to be satisfactory for the estimation of the constant n, but only under certain conditions for the constant Vi.