Novel multifunctional optical‐fiber probe: I. Development and validation

Liu, Jinzhong; Grace, John R.; Bi, Xiaotao

doi:10.1002/aic.690490607

Cited by 109 publications

(81 citation statements)

References 12 publications

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“…The optical probes developed for this study are based on backscattering principle (Liu et al, 2003). The optical fiber probes (OFP) were made of two standard step index plastic optical fibers (emitter and receiver fibers) embedded in a metallic coil of 3 mm external diameter.…”

Section: Experimental Set-upsupporting

confidence: 39%

Experimental and computational study on the bubble behavior in a 3-D fluidized bed

Acosta-Iborra

Sobrino

Hernández-Jiménez

et al. 2011

Chemical Engineering Science

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a b s t r a c tThe results from a two fluid Eulerian Eulerian three dimensional (3 D) simulation of a cylindrical bed, filled with Geldart B particles and fluidized with air in the bubbling regime, are compared with experimental data obtained from pressure and optical probe measurements in a real bed of similar dimensions and operative conditions. The main objectives of this comparison are to test the validity of the simulation results and to characterize the bubble behavior and bed dynamics. The fluidized bed is 0.193 m internal diameter and 0.8 m height, and it is filled with silica sand particles, reaching a settle height of 0.22 m. A frequency domain analysis of absolute and differential pressure signals in both the measured and the simulated cases shows that the same principal phenomena are reproduced with similar distributions of peak frequencies in the power spectral density (PSD) and width of the spectrum. The local dynamic behavior is also studied in the present work by means of the PSD of the simulated particle fraction and the PSD of the measured optical signal, which reveals as well good agreement between both the spectra. This work also presents, for the first time, comparative results of the measured and the simulated bubble size and velocity in a fully 3 D bed configuration. The values of bubble pierced length and velocity retrieved from the experimental optical signals and from the simulated particle fraction compare fairly well in different radial and axial positions. Very similar values are obtained when these bubble parameters are deduced from either simulated pressure signals or simulated particle volume fraction. In addition, applying the maximum entropy method technique, bubble size probability density functions are also calculated. All these results indicate that the two fluid model is able to reproduce the essential dynamics and interaction between bubbles and dense phase in the 3 D bed studied.

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Section: Experimental Set-upsupporting

confidence: 39%

Experimental and computational study on the bubble behavior in a 3-D fluidized bed

Acosta-Iborra

Sobrino

Hernández-Jiménez

et al. 2011

Chemical Engineering Science

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“…4, it is possible to specify limits of the penetration depth. For a distance of 5 mm the signal intensity falls about a 10% its maximum value, hence this may be considered the outer limit of the measuring volume of the probe (Liu et al, 2003). The optical probes have to be placed perpendicular to the flow to preclude the light reflected at the bottom of the bubble from affecting the determination of the time instant the probe leaves the bubble (see Fig.…”

Section: Optical Probessupporting

confidence: 37%

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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“…LEDs, a high pulsation frequency can easily be achieved, effectively removing background noise without compromising the sampling rate. Liu et al (2003) used a reflection type probe to measure both the solids concentration close to the probe as well as the solids velocity, thus obtaining the local solids flux. They used a three-fiber arrangement, with the sending fiber in the center.…”

Section: X-ray and Gamma-ray Tomographymentioning

confidence: 46%

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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Novel multifunctional optical‐fiber probe: I. Development and validation

Cited by 109 publications

References 12 publications

Experimental and computational study on the bubble behavior in a 3-D fluidized bed

Experimental and computational study on the bubble behavior in a 3-D fluidized bed

Maximum entropy estimation of the bubble size distribution in fluidized beds

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

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