Application of a gamma-radiation density gauge for determining hydrodynamic properties of fluidized beds

Weimer, Alan W.; Gyure, Dale C.; Clough, David E.

doi:10.1016/0032-5910(85)87025-x

Cited by 28 publications

(9 citation statements)

References 7 publications

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“…Only one source is used, either in combination with a single detector (single beam arrangement, Weimer et al, 1985, Mudde et al, 1999, Bhusarapu et al, 2004 O"Hern et al, 2005, Tortora et al, 2006. The former requires a single traverse through the slice of interest; the latter provides these data in one capture.…”

Section: X-ray and Gamma-ray Tomographymentioning

confidence: 99%

Measuring the Gas-Solids Distribution in Fluidized Beds -- A Review

Ommen¹,

Mudde²

2008

International Journal of Chemical Reactor Engineering

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In gas-solid fluidized beds, the distribution of the particles typically varies both in time and space. Since the gas-solids distribution and its variation have a strong influence on the performance of a fluidized bed for a given process, it is very important to accurately measure the gas-solids or voidage distribution. This paper reviews techniques for measuring the voidage distribution in gas-solid fluidized beds, with a focus on the developments during the last ten years. We will treat subsequently direct visualisation, tomography, optical probes, capacitance probes, and pressure measurements.Dense gas-solids flows are typically opaque to visible light. This makes optical techniques only of limited use in dense gas-solids flow. However, direct visualization can be useful for very dilute systems, pseudo 2-D beds, and the outer layer of dense, 3-D systems. Tomography is frequently used to obtain the voidage distribution in a horizontal cross-section of the bed. Electric capacitance tomography is fast, but its spatial resolution is limited and image reconstruction is still troublesome. Although some steps forward have been made, research is continuing at this point. For nuclear (X-ray and gamma-ray) tomography, the image reconstruction is much easier and the spatial resolution better, but its temporal resolution is typically much lower. Therefore, research efforts for nuclear tomography are mainly aimed at increasing the measurement frequency. Optical probes determine the voidage as a function of time in a small measurement volume, either by the degree of reflection or by the degree of transmission of a light bundle. Capacitance probes determine the voidage as a function of time in a small measurement volume by measuring the dielectric permittivity of the gas-solids suspension in the measurement volume. Both optical and capacitance probe techniques are reasonably well-developed; the current research effort spent at improving them seems * We would like to thank M.O. Coppens, J. Nijenhuis, R.W.S Bohlken, and M.A. Wormsbecker for useful suggestions during preparation of this manuscript. limited, especially for capacitance probes. Time-averaged pressure measurements are commonly used to determine the average bed density and bed height. By sampling the local pressure at a sufficiently high frequency (typically in the order of 200 Hz), much more information can be obtained about the fluidized bed hydrodynamics. However, obtaining quantitative voidage data from pressure fluctuations measurement remains a difficult task; in-bed pressure fluctuation (and acoustic) measurements are mostly used to determine changes in the voidage dynamics and distribution.

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Section: X-ray and Gamma-ray Tomographymentioning

confidence: 99%

Measuring the Gas-Solids Distribution in Fluidized Beds -- A Review

Ommen¹,

Mudde²

2008

International Journal of Chemical Reactor Engineering

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“…Lee et al (1985) have attempted to better define the liquid surface by using a wooden buoy, interfaced to a digital sensor that floats on the surface and is not significantly affected by liquid splashing. Weimer et al (1985) used a gamma-radiation density gauge to obtain the height of a fluidized bed as a funciton of time once gas flow was cut off. The latter technique does not require any visual observations and can be employed to study hydrodynamics of systems at high temperatures and/or high pressures.…”

Section: Experimental Techniquementioning

confidence: 99%

Holdup and interfacial area measurements using dynamic gas disengagement

1989

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The dynamic gas disengagement technique is discussed comprehensively in this paper. Also outlined is the procedure for estimating holdup structures and bubble rise velocities in a bubble column, which is extended to include the methodology for estimating the Sauter mean bubble diameter and therefore the specific gas-liquid interfacial area. The error limits for the estimated quantities are established using two extreme cases to describe the disengagement process: constant rate disengagement and interactive disengagement of bubbles. The analysis is done assuming a bimodal bubble size distribution; however, generalized equations for a multimodal bubble size distribution are also presented. Sensitivity of results to the two cases is illustrated using results obtained from experiments conducted with the air-tap water system in two bubble columns (0.05 and 0.23 m in diameter, 3 m tall). Sauter mean bubble diameters and specific interfacial areas estimated using the two approaches provide lower and upper limits for values reported in the literature.

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“…Therefore, it is difficult to translate data related to the initial particle velocities obtained from carefully injected bubbles to the ones obtained from ejected particles in freely bubbling fluidized beds. These results about the origin of ejected particles and bubble dynamics in fluidized beds have been obtained mostly in 2D fluidized beds, as 3D fluidized beds visual observations of bubble dynamics are impossible today, except for special experimental techniques as X-ray image [6] and g-radiation [7].…”

Section: Introductionmentioning

confidence: 99%

Initial particle velocity spatial distribution from 2-D erupting bubbles in fluidized beds

et al. 2005

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Some results on particle image velocimetry (PIV) in 2 D freely bubbling fluidized beds are presented. The PIV applications were used in order to determine the initial particle velocity of bubble eruptions. A two dimensional non reacting fluidized bed was constructed to measure the origin of the ejected particles and the initial particle velocity distribution, using coarse sand particles. The bubble ejection mechanism was observed taking into account the origin of particles ejected, the initial particle velocity distributions as well as the effect of other neighbor exploding bubbles. Our results show that the assumption of linear dependence of initial velocity with the angle predicts the velocity faithfully only for purely vertical ascent bubbles. Measurements of ejection velocities show that initial velocities in the combined layer are higher than those of the particles in the nose of the leading bubble. Avoiding coalescence of bubbles at the bed surface can lead to less particle entrainment out of the bed and consequently to shorter fluidized beds.

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Application of a gamma-radiation density gauge for determining hydrodynamic properties of fluidized beds

Cited by 28 publications

References 7 publications

Measuring the Gas-Solids Distribution in Fluidized Beds -- A Review

Measuring the Gas-Solids Distribution in Fluidized Beds -- A Review

Holdup and interfacial area measurements using dynamic gas disengagement

Initial particle velocity spatial distribution from 2-D erupting bubbles in fluidized beds

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