Particle Fluctuation Velocity in Gas Fluidized Beds - Fundamental Models Compared to Recent Experimental Data

2000 ◽  
Vol 627 ◽  
Author(s):  
G. D. Cody
Keyword(s):  
Fluidized Beds ◽  
Gas Flow ◽  
Vibrational Energy ◽  
Particle Diameter ◽  
Power Spectral Analysis ◽  
Recent Experimental Data ◽  
Granular Temperature ◽  
Fluctuation Velocity ◽  
Gas Fluidized Beds ◽  
Random Particle

ABSTRACTThe first measurements of the mean squared fluctuation velocity, or granular temperature, of monodispersed glass spheres in gas fluidized beds were recently obtained by two independent techniques: Power Spectral analysis of wall vibrational energy excited by random particle impact or Acoustic Shot Noise (ASN), and Diffusing Wave Spectroscopy (DWS) of reflected laser light multiply scattered by random particle motion. We explore the relevance of this data to the initial stability of the uniform fluidized state and to recent fundamental models for the magnitude, gas flow, and particle diameter dependence of the steady state granular temperature.

Particle granular temperature in gas fluidized beds

1996 ◽  
Vol 87 (3) ◽  
pp. 211-232 ◽  
Author(s):  
G.D. Cody ◽  
D.J. Goldfarb ◽  
G.V. Storch ◽  
A.N. Norris
Keyword(s):  
Fluidized Beds ◽  
Granular Temperature ◽  
Gas Fluidized Beds

Particle pressures generated around bubbles in gas-fluidized beds

2002 ◽  
Vol 455 ◽  
pp. 103-127 ◽  
Author(s):  
KHURRAM RAHMAN ◽  
CHARLES S. CAMPBELL
Keyword(s):  
Fluidized Bed ◽  
Bubble Size ◽  
Fluidized Beds ◽  
Gas Flow ◽  
Solid Particles ◽  
Particle Phase ◽  
Fluid Mixture ◽  
Maximum Value ◽  
Particle Pressure ◽  
Gas Fluidized Beds

The particle pressure is the surface force in a particle/fluid mixture that is exerted solely by the particle phase. This paper presents measurements of the particle pressure on the faces of a two-dimensional gas-fluidized bed and gives insight into the mechanisms by which bubbles generate particle pressure. The particle pressure is measured by a specially designed ‘particle pressure transducer’. The results show that, around single bubbles, the most significant particle pressures are generated below and to the sides of the bubble and that these particle pressures steadily increase and reach a maximum value at bubble eruption. The dominant mechanism appears to be defluidization of material in the particle phase that results from the bubble attracting fluidizing gas away from the surrounding material; the surrounding material is no longer supported by the gas flow and can only be supported across interparticle contacts which results in the observed particle pressures. The contribution of particle motion to particle pressure generation is insignificant.The magnitude of the particle pressure below a single bubble in a gas-fluidized bed depends on the bubble size and the density of the solid particles, as might be expected as the amount of gas attracted by the bubble should increase with bubble size and because the weight of defluidized material depends on the density of the solid material. A simple scaling of these quantities is suggested that is otherwise independent of the bed material.In freely bubbling gas-fluidized beds the particle pressures generated behave differently. Overall they are smaller in magnitude and reach their maximum value soon after the bubble passes instead of at eruption. In this situation, it appears that the bubbles interact with one another in such a way that the de uidization effect below a leading bubble is largely counteracted by refluidizing gas exiting the roof of trailing bubbles.

A Correlation for Maximum Heat Transfer to Cylinders and Spheres in Gas-Fluidized Beds

2018 ◽  
Author(s):  
Mirza M. Shah
Keyword(s):  
Heat Transfer ◽  
Fluidized Beds ◽  
Particle Diameter ◽  
Absolute Deviation ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Surface Diameter ◽  
Data Points ◽  
Gas Fluidized Beds ◽  
Cylinders And Spheres

A general correlation is presented for predicting maximum heat transfer coefficient for surfaces submerged in gas-fluidized beds. It has been verified with data for horizontal and vertical cylinders and spheres in beds of a wide variety of particles and gases. The gases include air, cryogens, methane, CO2, ammonia, and R-12. The range of parameters includes: heat transfer surface diameter 0.05 to 220 mm, particle diameter 31 to 15000 μm, pressure 0.026 to 0.95 MPa, and temperature 13 to 1028 °C. The 363 data points from 53 sources are predicted with a mean absolute deviation of 16.2 %. Several other correlations were also compared to the same data but had much larger deviations.

Discontinuity in Particle Granular Temperature Observed in Gas Fluidized Beds Across The Geldart B/A Boundary - Implications for Stability and Properties of the Geldart A Phase

1996 ◽  
Vol 464 ◽  
Author(s):  
George D. Cody ◽  
David J. Goldfarb
Keyword(s):  
Experimental Data ◽  
Gas Flow ◽  
Granular Temperature ◽  
Average Particle ◽  
Sphere Diameter ◽  
Langevin Model ◽  
Glass Spheres ◽  
Gas Fluidized Beds ◽  
The One ◽  
Fluidized Particles

ABSTRACTWe present new experimental data on the properties of monodispersed glass spheresas a function of sphere diameter and gas flow in a gas fluidized bed. The data obtained by a novel non-intrusive probe of the average particle kinetic energy, or granular temperature, at thewall is used to explore and understand the well known empirical distinction between fluidized particles which exhibit a single phase state at initial fluidization (Geldart A powders) and fluidized particles that exhibit gas bubbles at initial fluidization (Geldart B powders). Specifically we show that the experimental “jump” we observe in the granular temperature atthe Geldart / transition is sufficient to account for the initial stability of the Geldart A phase on the basis of the one dimensional, first order, two wave, stability theory first introduced by Jackson in the early sixties. We present new data on the diameter dependent properties of the glass spheres during bed collapse and bed expansion, which demonstrate the distinctionbetween Geldart A and B behavior for these monodispersed glass spheres. Finally we present a simple Langevin model to account for the dependence of the granular temperature on sphere diameter and gas flow, and discuss the implications of these new experimental data for the fundamental physics of the Geldart A phase.

Spatially resolved measurement of anisotropic granular temperature in gas-fluidized beds

2008 ◽  
Vol 182 (2) ◽  
pp. 171-181 ◽  
Author(s):  
D.J. Holland ◽  
C.R. Müller ◽  
J.S. Dennis ◽  
L.F. Gladden ◽  
A.J. Sederman
Keyword(s):  
Fluidized Beds ◽  
Granular Temperature ◽  
Spatially Resolved ◽  
Gas Fluidized Beds
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