Hydrodynamics of Pulsed Fluidized Bed of Ultrafine Powder: Fully Collapsing Fluidized Bed

The processing of fine and ultrafine particles using a fluidized bed is challenging in view of their unpredictable hydrodynamic behavior due to interparticle forces. The use of assisted fluidization techniques in such cases can be effective in improving the bed hydrodynamics. This work investigates the dynamics of pulsed fluidized bed of ultrafine nanosilica subjected to square-wave flow pulsations. The pulse duration used in this study is sufficient to allow the complete collapse of the pulsed fluidized bed between two consecutive flow pulsations. The proposed pulsation strategy is carefully implemented using electronic mass flow controllers with the help of analog output signals from data acquisition system. Given that the different regions of the fluidized bed exhibit varying dynamics, which together contribute to overall bed dynamics, the bed transients in the upper, central, and lower regions of the fluidized bed are monitored using several sensitive pressure transducers located along the height of the bed. The effect of the flow pulsation on the hydrodynamics of the fluidized bed is rigorously characterized. A significant reduction in the minimum fluidization velocity was obtained and an increase in the bed homogeneity was observed due to flow pulsations. The frequency domain analysis of the signals clearly delineated the frequency of the various events occurring during the fluidization.

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Deagglomeration of Ultrafine Hydrophilic Nanopowder Using Low-Frequency Pulsed Fluidization

Nanomaterials ◽

10.3390/nano10020388 ◽

2020 ◽

Vol 10 (2) ◽

pp. 388 ◽

Cited By ~ 2

Author(s):

Ebrahim H. Al-Ghurabi ◽

Mohammed Shahabuddin ◽

Nadavala Siva Kumar ◽

Mohammad Asif

Keyword(s):

Fluidized Bed ◽

Low Frequency ◽

Frequency Domain Analysis ◽

Wave Flow ◽

Velocity Change ◽

Pressure Transducers ◽

Wide Range ◽

Transient Data ◽

Flow Pulsations ◽

Sensitive Pressure

Low-frequency flow pulsations were utilized to improve the hydrodynamics of the fluidized bed of hydrophilic ultrafine nanosilica powder with strong agglomeration behavior. A gradual fluidization of unassisted fluidized bed through stepwise velocity change was carried out over a wide range of velocities followed by a gradual defluidization process. Bed dynamics in different regions of the fluidized bed were carefully monitored using fast and sensitive pressure transducers. Next, 0.05-Hz square-wave flow pulsation was introduced, and the fluidization behavior of the pulsed fluidized bed was rigorously characterized to delineate its effect on the bed hydrodynamics by comparing it with one of the unassisted fluidized bed. Flow pulsations caused a substantial decrease in minimum fluidization velocity and effective agglomerate diameter. The frequencies and amplitudes of various events in different fluidized bed regions were determined by performing frequency domain analysis on real-time bed transient data. The pulsations and their effects promoted deagglomeration and improved homogeneity of the pulsed fluidized bed.

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Nanopowder Fluidization Using the Combined Assisted Fluidization Techniques of Particle Mixing and Flow Pulsation

Applied Sciences ◽

10.3390/app9030572 ◽

2019 ◽

Vol 9 (3) ◽

pp. 572 ◽

Cited By ~ 4

Author(s):

Syed Ali ◽

Avijit Basu ◽

Sulaiman Alfadul ◽

Mohammad Asif

Keyword(s):

Fluidized Bed ◽

Gas Flow ◽

Substantial Reduction ◽

Data Acquisition System ◽

Gas Flow Rate ◽

Flow Pulsation ◽

Pressure Transducers ◽

Particle Mixing ◽

Group A ◽

Sensitive Pressure

In the present study, we report the fluidization behavior of ultrafine nanopowder using the assisted fluidization technique of particle mixing, which was further superimposed with the pulsation of the inlet gas flow to the fluidized bed. The powder selected in the present study was hydrophilic nanosilica, which shows strong agglomeration behavior leading to poor fluidization hydrodynamics. For particle mixing, small proportions of inert particles of Geldart group A classification were used. The inlet gas flow to the fluidized bed was pulsed with a square wave of frequency 0.1 Hz with the help of a solenoid valve controlled using the data acquisition system (DAQ). In addition to the gas flow rate to the fluidized bed, pressure transients were carefully monitored using sensitive pressure transducers connected to the DAQ. Our results indicate a substantial reduction in the effective agglomerate size as a result of the simultaneous implementation of the assisted fluidization techniques of particle mixing and flow pulsation.

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Morphology and structure analyses of SnO2 thin film coated on Al2O3 ultrafine particles by gas phase reaction in fluidized bed

Journal of Shanghai University (English Edition) ◽

10.1007/s11741-999-0031-6 ◽

1999 ◽

Vol 3 (1) ◽

pp. 62-65

Author(s):

Bin Hua ◽

Liyi Shi ◽

Chunzhong Li

Keyword(s):

Thin Film ◽

Gas Phase ◽

Fluidized Bed ◽

Ultrafine Particles ◽

Sno2 Thin Film ◽

Phase Reaction ◽

Gas Phase Reaction ◽

Morphology And Structure

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Horizontal Pressure Fluctuation in Bubbling Fluidized Bed

17th International Conference on Fluidized Bed Combustion ◽

10.1115/fbc2003-046 ◽

2003 ◽

Author(s):

Vesa V. Walle´n

Keyword(s):

Pressure Gradient ◽

Fluidized Bed ◽

Pressure Fluctuation ◽

Pressure Fluctuations ◽

Middle Part ◽

Biomass Combustion ◽

Bottom Part ◽

Pressure Transducers ◽

Bubbling Fluidized Bed ◽

Horizontal Pressure

Pressure measurements were conducted in a two-dimensional hot atmospheric bubbling fluidized bed reactor in the laboratory of Energy and Process Engineering at Tampere University of Technology. A set of six fast pressure transducers was used to detect the rapid pressure fluctuations inside the bubbling bed of the reactor. These pressure transducers were placed both vertically and horizontally into the reactor. From these measurements it was found that the vertical pressure fluctuation took place at the same time at different levels of the bed. Also the same fluctuation could be seen under the air distributor. The horizontal pressure fluctuation was found to vary both by place and time. At the bottom part of the bed the highest pressure peaks was found at centre of the bed. Most of the time there was a pressure gradient the highest pressure being in the centre of the bed. This gradient creates horizontal flow of gases from middle to the sides. The velocity of this flow varies with the size of the pressure gradient. The opposite effect can be found in the upper part of the bed. The highest pressure was no more in the middle part of the bed. Instead, it was found to be between the centre of the bed and left and right walls. The pressure was low at the walls but also rather low at the middle of the bed. There must be flow towards the walls and to the centre axis. These pressure fluctuations can provide an explanation for the well-known “wandering plume” effect. They can also give a tool to better describe the mixing inside a bubbling fluidized bed. This kind of tool is needed when biomass combustion is modelled in bubbling fluidized bed.

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Fluidization, Mixing and Segregation of a Biomass-Sand Mixture in a Fluidized Bed

International Journal of Chemical Reactor Engineering ◽

10.2202/1542-6580.1809 ◽

2008 ◽

Vol 6 (1) ◽

Cited By ~ 8

Author(s):

Yong Zhang ◽

Baosheng Jin ◽

Wenqi Zhong

Keyword(s):

Fluidized Bed ◽

Pressure Fluctuation ◽

Visual Observation ◽

Fluctuation Analysis ◽

Mixing Ratio ◽

Dynamic Features ◽

Pressure Transducers ◽

Sand Mixture ◽

Wide Range ◽

Initial Packing

Fluidization, mixing and segregation of a biomass-sand mixture in a 3D gas-fluidized bed have been investigated by means of visual observation, pressure fluctuation analysis and the bed-frozen method. Three types of mixtures are considered, in which biomass is a thin long stalk, and sand belongs to the Geldart B category. Experiments are carried out in a segmented fluidized bed equipped with multiple pressure transducers. Three initial packing conditions and two experiment procedures are used. The fluidization velocity varies to cover a wide range. Results show that in the local fluidization region, the mixing and segregation patterns are sensitive to the initial packing condition. In the case of a fully segregated state with biomass at the bottom, the bed inversion can be significantly observed due to the great segregation tendency of biomass. Further analyses indicate that the mixing ratio exerts a subtle influence on the competition between mixing and segregation by disturbing the coalescence and break-up of the bubble. In addition, the pressure fluctuation signal proves to be helpful in understanding the dynamic features of the phenomenology.

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