The Investigation On Flow Characteristic Of In Gas-solid Micro-scale Fluidized Bed

Because of the small dimensions of micro-scale fluidized beds (MFBs), the energyconsumption and waste effluent is decreased greatly. Thus，MFBs are characterized byexcellent heat and mass transfer efficiency, which can be used as catalytic and nonecatalytic reactors. The computational fluid dynamics (CFD) method has been interestedover the past years by many researchers, because it can obtain the data which is difficultfor experiment, optimize experimental apparatus, modify and testify numerical models,reduce experimental charge, and so on. Based on the Euerian two-fluid models,hydrodynamic in MFBs is numerical simulated by means of Fluent CFD software.Firstly, the fluidization characteristics of three different particles in MFBs with innerdiameters of30mm were investigated. The pressure sensor which was connected to acomputer online system，was used to measure the bed pressure drop and minimumfluidization velocity (umf). The results noted that some extra cohesive force betweenparticles need to be overcome when increasing gas velocity to fluidize particles, whichmakes the measured umfmuch more unstable in ascending run than descending run. Thecalculation values of bed pressure drop of Geldart group A in MFBs were higher than theexperimental values, but group B and D were contraries. The minimum fluidizationvelocity in MFBs was increased with increasing static bed height, but the amplitude wasdifferences.Secondly, the slugging characteristics of different particles were determined usingCFD code Fluent6.3combining experimental data measured in our lab. The sluggingfluidization of different particles was investigated using experimental and numericalsimulation methods in MFBs with height of30mm and inner diameter of300mm. It wasfound that a steady stable of group A developed and slugging phenomenon did not occur.The results of the transfer of slugging fluidization of group B, maximum bed expansionratio and pressure fluctuation were systemically investigated in a gas-solid fluidized bed.By comparing to the experimental datas, the simulation results can better predict the slugging fluidization characterization. Along with the increasing bed size, the bed becamemore stability and uniformity. Slugging also occurred in fluidized system of group D. Thecontinuous formation of large bubbles were formed in the bed layer and the fluctuationrange of bed pressure drop was serious.Finally, the bubbling characteristics of group B were systematically studied in MFBs.Then the parameters of gas-solid distribution, bed expansion ratio, bed pressure drop, et al,were systemically investigated in a gas-solid fluidized bed. The results were shown thatthe bed is rendered into a nonuniform flow state, which is based on multiple bubbles ofvarying sizes with interchange of gas and solids taking place between the bubble phaseand the emulsion phase. Moreover, appropriate setting of geometrical model, time step,particle restitution coefficient and drag model were obtained to decrease calculation errorby investigating the parameters effects on the calculation results. The choice wasdetermined using the2D model, the time step of0.0005s, particle collision coefficient ofrestitution of0.90, drag model using Syamlal-O’Brien model for optimum calculationparameters.