Origin, propagation and attenuation of pressure waves in gas—solid fluidized beds

Schaaf, van der Tw Tjerk; Schouten, JC Jaap; Bleek, van den Cm

doi:10.1016/s0032-5910(97)03341-x

Cited by 146 publications

(94 citation statements)

References 7 publications

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“…Even though several reports suggested that these high frequency methods can be tuned to serve for some fluidized bed applications, the sampling frequencies on the order of hundreds of kHz considerably can increase the computational costs needed to handle the monitoring problem. In addition, this approach disregards two important factors, such as the compression waves (van der Schaaf et al, 1998) and the structural vessel dynamics, which might affect the measurement of flow-induced vibration resulting from the fluidized bed dynamics, as discussed below. Consequently, the use of a theory based solely on "elastic waves" as the single source of "Acoustic Emissions ( AE)" cannot be easily extended to other FB systems and does not explain the most recent research results in the field (Abbasi et al, 2009;Cody et al, 1996;Cody et al, 2000;de Martin et al, 2010;de Martin et al, 2011;Li et al, 2011).…”

Section: Flow-induced Vibration In Fluidized Bedsmentioning

confidence: 99%

“…The origin and the propagation of pressure waves in fluidized beds have been the subject of substantial research efforts (Bi et al, 1995;Musmarra et al, 1995;Roy et al, 1990;van der Schaaf et al, 1998). The propagating pressure waves, which are mainly a result of the fluctuations in gas or particle velocities and to local changes in the bed voidage, are coupled with "forced fluidized bed oscillations", leading to an acoustic wave pattern characterized by a natural period of the pressure oscillation, t n .…”

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confidence: 99%

“…The separated flow theory has been reported to be more appropriate in accounting for c s with the observed effects of the wave frequency and the particle size (i.e. elastic waves) (Bi et al, 1995;van der Schaaf et al, 1998). In this paper, the separated-flow compressiblewave theory is used to characterize the natural frequency of the bed.…”

mentioning

confidence: 99%

“…3 was taken from the quarter of the period of the wave frequency estimated from the pseudo-homogeneous approach (eq. 2) (van der Schaaf et al, 1998), with the resulting c s value used to compute a new natural period (eq. 2) and so on.…”

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confidence: 99%

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Characterization of flow-induced vibrations in gas–solid fluidized beds: Elements of the theory

Briongos

Sobrino

Gómez-Hernández

et al. 2013

Chemical Engineering Science

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Abstract:This paper revisits the basic hypothesis underlying the measurement of flow-induced vibration in fluidized beds. A novel theoretical approach based on the standing pressure field characterizing the bed dynamics is proposed to link the pressure fluctuations to the measured accelerometer signals. The model provides a reliable prediction of the carrying frequency band and helps in designing the accelerometer measurement process.The model was tested with previous results reported in the literature as well as with piezoelectric accelerometer measurements collected from a lab-scale experimental facility. A study on accelerometer measurements was conducted to identify the main limitations expected for measuring flow-induced vibrations in a gas-solid fluidized bed.The structural response of the vessel to flow-induced vibration was mostly determined by the "bed acoustics" that can be dominated by either elastic or compression waves.Finally, the survival of an envelope process on the measured accelerometer signal guaranteed the quality of the flow dynamical information collected during the measurement process.

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Section: Flow-induced Vibration In Fluidized Bedsmentioning

confidence: 99%

mentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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Characterization of flow-induced vibrations in gas–solid fluidized beds: Elements of the theory

Briongos

Sobrino

Gómez-Hernández

et al. 2013

Chemical Engineering Science

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“…Compression waves can propagate both upwards and downwards through the bed. In a small diameter fluidized bed, the amplitude of a downward travelling compression wave stays constant; the amplitude of an upward travelling compression wave decreases linearly to zero at the bed surface (van der Schaaf et al, 1998). The fast-travelling compression waves can originate from a number of sources: a.…”

Section: Origin Of Pressure Fluctuationsmentioning

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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