Digital image analysis measurements of bed expansion and segregation dynamics in dense gas-fluidised beds

Goldschmidt, Mjv; Link, JM; Mellema, S; Kuipers, J.A.M.

doi:10.1016/j.powtec.2003.09.003

Cited by 190 publications

(166 citation statements)

References 17 publications

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“…The size of the picture captured from the central region of the bed with the camera is approximately 0.20 × 0.25 m. Thus, only a small section of the bed is captured in order to get a high spatial resolution. The white picture is similar to the one obtained by Goldschmidt et al [12] who used it to correct local light intensities in their segregation study. A lighter region appears in the center of the image.…”

Section: Experimental Set-up and Calibrationsupporting

confidence: 76%

“…One with the empty bed and another one with the bed slightly under minimum fluidization conditions in order to avoid the presence of bubbles. The grey level obtained with the empty bed was used as a spatial calibration of voidage ε =1 [12]. The grey map obtained from the pictures at minimum fluidization conditions is ε mf .…”

Section: Experimental Set-up and Calibrationmentioning

confidence: 99%

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Voidage distribution around bubbles in a fluidized bed: Influence on throughflow

et al. 2010

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a b s t r a c tIn this work, a new method for measuring void fraction distribution around endogenous bubbles in a 2D fluidized bed is presented. The technique is based on illuminating a transparent wall 2 dimensional bed with diffuse light from the rear and recording the distribution of light that penetrates the bed. The recording is made with a high speed video camera, which gives frames with grey level corresponding to the light penetration and from which the voidage distribution around the bubbles can be determined. In this way, voidage distribution in the region very close to the bubble contour (r/R b ≲ 1.2) is obtained, which was not possible in previous studies due to limitations in spatial resolution. A correlation is proposed for the voidage at the contour of the bubble, with the voidage depending on the radial position and the polar angle ε(r, θ). In addition, the effect of the voidage distribution on the throughflow crossing the bubbles was studied and an increase of 20% was determined for the average bubble geometry of the more than 100 bubbles analysed.

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Section: Experimental Set-up and Calibrationsupporting

confidence: 76%

Section: Experimental Set-up and Calibrationmentioning

confidence: 99%

Voidage distribution around bubbles in a fluidized bed: Influence on throughflow

et al. 2010

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“…Goldschmidt et al [14] used this technique to detect particles and Link et al [5] successfully applied DIA to study spout-fluidized beds. In this work, the particles are detected with the use of DIA, and additionally, a new algorithm is proposed to determine the volume fraction of particles in each interrogation area.…”

Section: Digital Image Analysismentioning

confidence: 99%

An experimental study of the effect of collision properties on spout fluidized bed dynamics

et al. 2011

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In this paper we experimentally study the effect of collision properties of different particle systems on the bed dynamics of a spout fluidized bed. This is done in different flow regimes: the spout-fluidization regime (case A), the jet-in-fluidized-bed regime (case B) and the spouting-with-aeration regime (case C). The considered particle systems comprise glass beads, γ-alumina oxide and zeolite 4A particles, which are all classified as Geldart D. A non-intrusive measurement technique is used, viz. particle image velocimetry (PIV) to measure the particle flow field in a pseudo two-dimensional (2D) spout fluidized bed. Additionally, digital images are analyzed using a newly developed digital image analysis (DIA) algorithm to evaluate the particle volume fraction. It is demonstrated that the new proposed DIA algorithm provides reliable information on the particle volume fraction, showing that it is a powerful tool when combined with PIV. The added value of DIA is confirmed by comparing the particle velocity fields and volumetric particle fluxes. The particle fluxes display only small differences between the particle systems for each of the examined flow regimes, with the largest difference in the jet-in-fluidized bed regime. In this regime, the flow behaviour of the zeolite 4A particles does not show any features of the spout fluidized bed anymore, but behaviour of an ordinary fluidized bed. This is due to the direct bubble formation above the bottom plate, which results in a large disturbance near the spout entrance. It seems that zeolite 4A particles -because of their small restitution coefficient-tend to cluster in a more pronounced way, producing more bubbles compared to glass beads and γ-alumina oxide particles.

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“…Image processing can be used to improve the quality of obtained recording (e.g., Lackermeier et al, 2001). In addition, it can be used to extract quantitative information, for example about the bubble size and velocity (Lim et al, 1990, Mudde et al, 1994 or the segregation of particles (Goldschmidt et al, 2003) in pseudo 2-D beds. While the translation of results obtained in pseudo 2-D beds to 3-D systems must be done with caution, the use of pseudo 2-D beds can be valuable for, e.g., calibration of other types of measurement equipment and for validation of simulation codes.…”

Section: Direct Visualisationmentioning

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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Digital image analysis measurements of bed expansion and segregation dynamics in dense gas-fluidised beds

Cited by 190 publications

References 17 publications

Voidage distribution around bubbles in a fluidized bed: Influence on throughflow

Voidage distribution around bubbles in a fluidized bed: Influence on throughflow

An experimental study of the effect of collision properties on spout fluidized bed dynamics

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

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