Effect Of Bed Height Research Articles

A fractal analysis of solids mixing in two-dimensional vibrating particle beds

Using flow visualization and digital image processing we have shown experimentally that convective motions and mixing of particles within vertically vibrating two-dimensional particle beds are amenable to characterization by fractal properties. The time profile of a fractal dimension presents quantitative information on the rate and degree of mixing. Thus, the fractal dimension has been used to show the variation in the rate of mixing along the bed height. Numerical studies based on molecular dynamics simulations confirmed the fractal properties of the system. The effect of bed height on the regional variations in the rate of mixing is explained in terms of kinetic energy per particle.

Tensile strength of wet granula materials

The dimensionless tensile strength σd/ α of wet granular materials with saturation levels in the plateau region of the pendular state was correlated with the void fraction of the agglomerate. The correlation fitted well with experimental measurements carried out on glass beads of diameter 93 μm and with literature data, and was an improvement over the traditional Rumpf model. The tensile strength at other saturations could be easily derived from the proposed correlation. The effects of bed height in the tester cell, liquid saturation levels in the agglomerate, chemical additives and non-uniformity of the packing of the powder mass were also investigated.

Fluidized Bed Drying of Large Particles

Batch drying of red spring wheat in a fluidized bed was performed. Effects of bed height, gas velocity, initial moisture content and air temperature on drying rate were investigated. Wheat was conditioned to simulate high moisture contents just after harvest. Heated air was the medium for moisture removal with thermocouples located along the height of the freeboard recording bed temperatures. Samples were removed at regular intervals during drying and their moisture contents determined. It was found that the rate of moisture removal was controlled by the internal rate of diffusion and hence slugging had no effect on the drying rate. The temperature distribution within the bed was uniform due to the high degree of mixing that occurs as wall slugs are formed with wheat. At lower bed temperatures the rate of drying slowed considerably. Drying times were considerably shorter than other drying apparatus.

Application of fuzzy logic to bed height control in agitation-fluidized bed granulation

Development of a new technique for producing spherical and well-compacted granules, and the application of fuzzy control to a fluidized bed granulation process are described. An agitation-fluidized bed, a type of fluidized bed equipped with an agitator blade, was used for granulation; bed height was controlled by fuzzy logic based on a linguistic algorithm employing IF—THEN rules, to maintain a constant bed height and impart effective agitation to the granules. It was shown that bed height control was effective in preventing defluidization and channeling, and was necessary for automatic operation. The effects of bed height and agitator rotational speed on granule properties, such as apparent density, and on granule shape were investigated. A new technique is proposed for utilizing bed height control to produce spherical and well-compacted granules, which cannot be done using conventional fluidized bed techniques.

Effect of bed height on simultaneous heat and mass transfer in a two-dimensional spouted bed dryer

The drying kinetics of shelled corn was studied in a laboratory-scale two dimensional spouted bed dryer equipped with draft plates. The effect of bed height on drying rate is interpreted in terms of the heat and mass transfer mechanism with unsteady diffusion being dominant in moisture transport. The relevant apparent diffusion coefficient is evaluated from Fick's equation in spherical coordinates approaching sufficiently the geometry of a single grain, and related to the height of a bulk of grain. Page's equation is found to adequately describe the drying kinetics of the bulk of grain if parameters of this equation are related to the bed height.

超微粒子の一軸圧縮過程における圧力伝達特性及び層内部構造の変化

Ultrafine Fe particles with a chain-like structure and TiO2 and MgO particles of four different sizes with a lumpy structure were packed by uniaxial compression. The effects of bed height and particle size on the compression characteristics of the packed bed, the stress transmission characteristics of the bed, the pore size distribution of the bed and radial distribution of stress at the bottom of the bed were investigated. The characteristic curve of the stress transmission can be explained from the change in pore-size distributions of the bed measured by a mercury porosimeter. The bed voidage can be correlated well with the applied stress by Modified Cooper's Equation with three terms. The three terms are found to be represented by three regions in a stress transition characteristic curve and change by the change of measured pore size distribution. It is found that the stress transmission through the bed increases with increase in particle size.

Effect of bed height on particle entrainment from gas-fluidized beds

Both the flux of particles ejected from a fluidized bed and the flux of particles entrained above the TDH increase when the bed height increases. Tracer measurements confirmed that jets of particles are ejected from the bed only when two or more bubbles coalesce near the bed surface. A new model which accounts for ‘Gulf Streaming’ effects can predict the flux of ejected particles.

Some aerodynamic and solids circulation measurements in a slotted spouted bed of grains

Pressure drop, minimum circulation velocity and solids circulation rates were measured in a spouted bed with a slotted gas inlet and a draft tube formed by vertical partitions, for barley, peas, corn and wheat. Both full (symmetric) and half (asymmetric) configurations were examined. The presence of appropriately positioned vertical baffles was found to yield stable spouting and eliminate the upper limit on the maximum spoutable height. The solids circulation rate, which is equal to the solids entrainment rate by the spouting air jet, was observed to correlate directly with the square root of the air inlet velocity for all the grains studied. Effects of bed height, height and location of the vertical baffle(s) and the inlet slot width on the bed pressure drop and solids circulation rate are documented and discussed.

Convective Cooling of Simulated Core Debris Beds

Natural convection heat transfer in simulated core debris beds has been examined. The debris beds are simulated using electrically heated packed tube bundles arranged in either a square or staggered lattice with porosities varying between 0.31 and 0.95. The effects of bed height, heat generation rate, particle size, porosity, overlying liquid layer height, and top surface boundary condition on the downward and upward power fractions and Nusselt numbers have been determined. Flow patterns within the bed and overlying fluid region have been visualized using particle tracing techniques. Correlations for the downward and upward Nusselt numbers, Nu /SUB B/ and Nu /SUB T/ , as functions of the internal Rayleigh number have been developed. In all cases, the beds are bounded from below by a cooled isothermal surface. When the overlying fluid is bounded from above by a cooled solid isothermal surface, the Nusselt numbers are given by Nu /SUB B/ = 0.424 Ra /SUP 0.226/ and Nu /SUB T/ = 1.61 Ra /SUP 0.220/ . When the upper surface of the overlying fluid is free, the downward Nusselt number is given by Nu /SUB B/ = 0.503 Ra /SUP 0.180/ . These correlations are valid for the ranges 10/sup 2/more » less than or equal to Ra less than or equal to 10/sup 7/ and 0.1 less than or equal to /eta/ less than or equal to 1.0, where /eta/ is the ratio between the heights of the overlying fluid layer and the bed.« less

Gas distributor in fluidised beds

Satisfactory performance of fluidised bed reactors in terms of bed characteristics, chemical conversion and power requirement for pumping the fluidising medium is influenced by the design features of gas distributors. In industrial practice multi-orifice types of distributors are frequently used. This paper presents the results of experiments carried out in a 100-mm-diam. glass column using multi-orifice plate distributors. The effect of bed height and bed materials on the number of operating orifices is reported. The number of operating orifices is found to be a function of gas velocity and the ratio of pressure drops across the distributor and the bed.