A gas−solid fluidized bed, 0.14 m in diameter and 1.6 m in height, was employed to investigate systematically the effects of perforated ratios of distributor on fluidization characteristics with air as gas phase and fluid catalytic cracking particles as solid phase. The distributions of the distributor pressure drop, solid particle concentration, and bed pressure drop were obtained by means of different perforated ratios of distributors. The particle concentration distribution and bed pressure drop were measured by a PV-6A particles velocity measurer and a U-manometer, respectively. The parameters of bed pressure drop, distributor pressure drop, the instantaneous evolution of bubbles, and profile of radial solid holdups adopted three perforated ratios of distributors were simulated using computational fluid dynamics code Fluent 6.2. The results showed that the distributor pressure drop decreased with increasing perforated ratios and decreasing superficial gas velocity. The global solid holdup decreased from the wall to center region, and it had parabolic concentration profile under pressure-driven force for different perforated ratios of three distributors investigated. However, the distribution of radial solid holdup was more homogeneous, and it had a better agreement with experiment values for perforated ratio 0.46% of distributor than that for perforated ratio 0.86 or 1.10% of distributors. The bubble size at the region of distributor decreased with increasing perforated ratio of distributors, and it had more obvious circulation motion of solid particles for the perforated ratio 0.46% of distributor than that for perforated ratio 0.86 or 1.10% of distributor. The bed pressure drop and root mean square (rms) of bed pressure drop in gas−solid fluidized bed appeared differently for three perforated ratios of distributors. The rms of bed pressure drop for the perforated ratio 0.46% of distributor was larger than that for perforated ratio 0.86 or 1.10% of distributors, and the larger discrepancy occurred as the perforated ratio of distributor was 0.46%. The numerical simulation results agreed well with the experimental data at low superficial gas velocity for calculation of distributor pressure drop. However, larger error occurred at high superficial gas velocity.

The gas-liquid-(solid) three-phase hydrodynamics in an external-loop airlift reactor (EL-ALR) with an upward pipe 0.47 m in diameter and 2.5 m in height, two external loop downward pipes 0.08 m in diameter and 2.5 m in height, were investigated using four different gas sparger designs. The microconductivity probe and the three-dimensional (3-D) laser Doppler anemometry (LDA) techniques were, respectively, implemented to measure the local gas holdup in the riser (R Gr ) and liquid phase velocity in the downcomer (U Ld ) using air as the gas phase, water as the liquid phase, and alginate gel beads as the solid phase, over a wide range of operation conditions. The tracer age distribution was measured using the pulse-pursuit response technology. Axial dispersion model (ADM) was used to estimate the model parameter Peclet number (Pe) values as a fitted parameter with the measured data, using the gold partition method for nonlinear programming strategy inequation restrict conditions. The ADM gave better fits to the experimental data at high axial locations and lower superficial gas velocity (U G ) for an EL-ALR used with a large L/D R ratio. A synergistic effect of U Ld , R Gr , Pe, solids loading (SL), and sparger designs on the performance of an EL-ALR was observed in our experiments. The sparger designs were determined to have a noticeable effect on the R Gr and Pe in the lower gas velocity and lower solid loading ranges (U G < 0.025 m/s and SL < 2%), but only a slight effect in the high gas velocity and high solid loading ranges (U G > 0.030 m/s and SL > 3%). However, the effect of sparger designs on the U Ld is greater in the gas velocity from 0.025 m/s to 0.045 m/s. For the lower solids loading, the increase of orifice diameter leads to a decrease in R Gr . This is in accordance with what was presented in the gas-liquid two-phase system. Moreover, the influence of orifice diameters of the spargers is negligible for solids loading of >3%. Although the Pe values decreased with the operating gas velocity, the gas velocity change from 0.03 m/s to 0.04 m/s yielded lower Pe values, as a result of the reduced bubble size. As the gas velocity further increased to 0.06 m/s, the R Gr and the U Ld values increased, while the Pe values negligibly increased. For a gas-liquid two-phase system, Pe decreases with the orifice diameter and, for 1% of solids, Pe is also lower for sparger P-2 (φ 0.6 mm) than for sparger P-1 (φ 0.3 mm). For higher amounts of solids (3%), Pe does not have a defined trend. In addition to the gas velocity and sparger design effects, the solids loading had the effect of decreasing the U Ld values, while such effect became small and flattened at high solid loadings. The U Ld values, especially with VO ) 100%, are 20% lower in three-phase flow than that in two-phase flow. In addition, the U Ld profiles in three-phase flow are flatter than that in two-phase flow with VO ) 50%-100%, actually showing a parabolic shape rather than the almost linear one encountered in two-phase flow. This is very important for ...

in Wiley InterScience (www.interscience.wiley.com).The effects of sound assistance on fluidization behaviors were systematically investigated in a gas-solid acoustic fluidized bed. A model modified from Syamlal-O'Brien drag model was established. The original solid momentum equation was developed and an acoustic model was also proposed. The radial particle volume fraction, axial root-mean-square of bed pressure drop, granular temperature, and particle velocity in gas-solid acoustic fluidized bed were simulated using computational fluid dynamics (CFD) code Fluent 6.2. The results showed that radial particle volume fraction increased using modified drag model compared with that using the original one. Radial particle volume fraction was revealed as a parabolic concentration profile. Axial particle volume fraction decreased with the increasing bed height. The granular temperature increased with increasing sound pressure level. It showed that simulation values using CFD code Fluent 6.2 were in agreement with the experimental data.

A gas−liquid external-loop airlift reactor with a riser 0.47 m in diameter and 2.5 m in height and two external-loop down-comers 0.08 m in diameter and 2.5 m in height were used to investigate the gas−liquid two-phase flow structure. Local phase holdups were measured simultaneously by a microconductivity probe with air as the gas phase and water as the liquid phase over a wide range of operation conditions. Liquid flow velocity measurements were performed using the electrolyte tracer measurement (ETM) technique. The hydrodynamics near the sparger zone, riser disengagement zone (zone 1), junction zone (zone 2), and down-comer disengagement zone (zone 3) were systematically examined using the CFDs at the local scale and at the riser scale, respectively. The simulation results showed that zones 1, 2, and 3 exhibit three different flow regimes, which were the secondary mixed flow regime, the mixed flow regime, and the homogeneous bubble regime, respectively. It was also indicated that turbulent kinetic energy and turbulent kinetic energy dissipation rate were influenced by a gas sparger. These results were necessary to explain these different regimes using computational fluid dynamics (CFD) to provide deeper insight at the local scale for reactor geometry, such as gas sparger, junction and disengagement zones as well as the gas−liquid phase flow microstructure. The simulation results at the local scale were difficult to obtain by experiment. The numerical simulating results of local gas holdup and local gas and liquid velocities agreed well with the experimental data at a low gas flow rate. However, large errors occurred in the simulations at a high gas flow rate, because of poor estimation of the influence of bubble-induced turbulence or the higher density of the tracer and the poor mesh refinement. The flow structure and turbulence parameters of the phases presented here were useful for designing gas−liquid external-loop airlift reactors.