Application of Fast X-ray CT Scanner to Visualization of Bubbles in Fluidized Bed.

Kai, Takami; Misawa, Masaki; Takahashi, Tetsuo; Tiseanu, Ion; Ichikawa, Naoki; Tsuji, Naoki

doi:10.1252/jcej.33.906

Cited by 28 publications

(23 citation statements)

References 10 publications

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“…In recent years the scanner has been modified and upgraded to a multi tube scanner, allowing for a much shorter scanning time: about 6ms for a 4mm by 4mm resolution in a column of 32cm to 24ms for a 1mm by 1mm resolution in the same column. Kai et al (2000) where also able to combine a high spatial resolution (pixels of only 0.15 mm 2 ) with short scanning times (4 ms), using 18 X-ray sources and 122 detectors. They showed that from the obtained data pseudo 3-dimensional images of the bubbles can be reconstructed (Kai et al, 2005).…”

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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“…Non-intrusive techniques such as X-ray (Kai et al, 2000) or magnetic resonance imaging (Müller et al, 2006) provide valuable information on bubbles in three-dimensional fluidized beds. However, they are expensive and limited to small equipment.…”

Section: Introductionmentioning

confidence: 99%

Maximum entropy estimation of the bubble size distribution in fluidized beds

Sobrino¹,

Almendros-Ibáñez²,

Santana³

et al. 2009

Chemical Engineering Science

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This work presents a new methodology, based on the maximum entropy method, to obtain bubble characteristics in fluidized beds. The probability distributions (PDF) of bubble pierced length and velocity are obtained applying the maximum entropy principle to experimental measurements. In addition, the bubble diameter distribution has been inferred from experimental pierced length measurements. This method is applied to characterize bubbles in fluidized beds for the first time and the most general bubble geometry, a truncated spheroid, is considered. The distance between probes, s, which is the minimum pierced length that is possible to measure accurately using intrusive probes, has been introduced as a constraint in the derivation of the size distribution equation. The maximum entropy method is applied to experimental measurements of bubble characteristics carried out using optical and pressure probes in a three-dimensional fluidized bed of Geldart B particles. Results on bubble size obtained from pressure and optical probes are very similar, although optical probes provide more local information and can be used at any position in the bed. The maximum entropy principle has been found to be a simple method that offers many advantages over other methods applied before for size distribution modeling in fluidized beds.

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“…A fast X-ray CT system with 60 independent switchable X-ray sources has been suggested in Hori, Fujimoto, and Kawanishi (1998) and a similar system with 18 X-ray sources having the frame rate of 250 frames/s in Kai et al (2000) and Misawa, Tiseanu, Prasser, and Ichikawa (2003). A slightly different approach enabling dual plane measurements with the speed of 100 frames/s has been introduced in Mudde (2011) andSaayman, Nicol, van Ommen, andMudde (2013).…”

Section: Optical Flow Metersmentioning

confidence: 99%