Wave propagation and granular temperature in fluidized beds of nanoparticles

2011

Ind. Eng. Chem. Res.

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Particle image velocimetry (PIV) experiments were performed noninvasively in the Illinois Institute of Technology (IIT) two-dimensional circulating fluidized bed (2-D CFB) of fluid catalytic cracking (FCC) particles to measure laminar and turbulent properties, near the front wall in the z-direction; at the center and near the right and left walls in the x-direction; and in the free board region in the y-direction. The PIV measurements were obtained simultaneously in the y- and x-axes, using a charge-coupled device (CCD) camera, with the aid of a colored rotating transparency. The instantaneous and hydrodynamic velocities were used to obtain laminar properties for particles and turbulent properties for clusters, respectively. Laminar and turbulent properties for solids conveyed anisotropy. The y-axis solids velocities, power spectral densities of hydrodynamic velocities, and granular temperatures were highest at the center in the x-direction. The mixing was on the level of particles. The y- and x-axes solids dispersion coefficients were several orders of magnitude lower than the literature values, because of the low particle velocities in the free board. However, total granular temperatures were reasonably close to the literature values.

Section: Laminar and Turbulent Propertiesmentioning

confidence: 89%

Section: Light Diode Assemblymentioning

confidence: 99%

Measurements of Dispersion Coefficients for FCC Particles in a Free Board

Kashyap

2011

Ind. Eng. Chem. Res.

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“…A light diode assembly has been used several times to understand the dynamics in fluidized beds by measuring solids volume fractions (Refs 26–29…”

Section: Experimental Procedures For the Measurements Of Mass Transfermentioning

confidence: 99%

Measurements and computation of low mass transfer coefficients for FCC particles with ozone decomposition reaction

Kashyap

2011

AIChE Journal

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in Wiley Online Library (wileyonlinelibrary.com).The mass transfer coefficients and Sherwood numbers for catalyzed fluid cracking catalyst particles were measured and computed in a two-dimensional (2-D) bubbling fluidized bed, with ozone decomposition reaction. The measured and computed Sherwood numbers, using 3-and 2-D kinetic theory based computational fluid dynamics simulations, were of the order of 10 À6 -10 À2. The low Sherwood numbers were in reasonable agreement with the literature data for small particles, at low Reynolds numbers. The computational fluid dynamics simulations showed that it is possible to compute conversions in fluidized bed reactors without using the conventional model with empirical mass transfer coefficients.

“…A series of experiments were conducted to understand the impact of a compression wave through a fluidized bed of 75-µm FCC particles. 21,22 The physical parameters for the system are defined in Table 1.…”

Section: Introductionmentioning

confidence: 99%

Porosity and Pressure Waves in a Fluidized Bed of FCC Particles

Driscoll

2008

Ind. Eng. Chem. Res.

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The speeds of motion of compression waves through a fluidized bed of 75-µm FCC particles between the minimum bubbling and the minimum fluidization velocities were determined by measuring the times of arrival of compression zones using a γ-ray densitometer. The theory of characteristics shows that this speed, which is on the order of 1.4 m/s, represents the maximum velocity of discharge of nonfluidized FCC particles. The velocity of these compression waves was used to calculate the solids stress modulus of the fluidized bed via the one-dimensional mass and momentum balances for granular flow. In addition, measurements of the pressure wave propagation produced a mixture sonic velocity that is an order of magnitude higher than the speeds of the solids compression wave. The sonic velocity of the homogeneous mixture, which is on the order of 20 m/s, gives the maximum achievable velocity for the circulation of FCC particles in a standpipe of a refinery. This study shows that there are two distinct waves that travel through the fluidized bed at significantly different velocities when the bed is subjected to a shock. A correlation for the solids stress modulus was determined as a function of void fraction. This new correlation was an input into the viscosity input gas-solid hydrodynamic model and yielded simulations that were consistent with the experimental observations and results. Using the complete equation of state for FCC particles and the relationship between the compression wave velocity and the solids stress modulus, the computed granular temperature is two orders of magnitude lower than the square of the wave propagation velocity and is consistent with literature values.