Periodic pressure fluctuations in fluidized beds

Verloop, J.; Heertjes, P.M.

doi:10.1016/0009-2509(74)80096-5

Cited by 102 publications

(47 citation statements)

References 4 publications

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“…This frequency has been shown to be related to the emergence of gas bubbles at the surface of the bed. Verloop and Heertjes (1974) reported that pressure fluctuations are similar to sinusoidal waves. Hiraoka et al (1984Hiraoka et al ( , 1986) developed a dynamic model to predict the dominant frequency of bed fluctuations.…”

Section: Introductionmentioning

confidence: 93%

Standard deviation of absolute and differential pressure fluctuations in fluidized beds of group B particles

Sobrino

Sánchez-Delgado

García-Hernando

et al. 2008

Chemical Engineering Research and Design

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Keywords: Fluidization; Gas-solid bed; Pressure fluctuations IntroductionKnowledge of bed fluctuations in a gas-solid fluidized bed is important for its design and/or operation as they provide information on indexes of fluidization quality, which include formation, rise and eruption of gas bubbles, movement of solids and pressure waves propagation through the bed. These indexes are commonly considered as an indicative of the dynamic behaviour of the fluidized bed and can be explored as a way of monitoring the process (Felipe and Rocha, 2007). Due to the ease of measurement and its significance in understanding dynamic behaviours, pressure time series and pressure fluctuations have been investigated by numerous researchers (Bi, 2007). It is accepted that the complex pressure signal is a result of the superposition of local fluctuations caused mainly by traveling gas bubbles and fast-traveling pressure waves arising due to bubble formation, coalescence and eruption. In order to characterize the hydrodynamics of the bed, statistical methods and spectral analysis have been used to identify these phenomena and to establish the different fluidization regimes (Lirag and Littman, 1971;Fan et al., 1981;Johnsson et al., 2000;van der Schaaf et al., 2002;Bai et al., 2005;Puncochar and Drahos, 2005 ity (Puncochar et al., 1985;Wilkinson, 1995;Felipe and Rocha, 2007). In spite of the measurement simplicity the nature of pressure fluctuations in a fluidized bed is a complex function of particle properties, bed geometry, flow conditions, pressure and temperature. Fan et al. (1981) investigated the effect of particle size, static bed height and gas velocity. Svoboda et al. (1984) showed that the magnitude of the pressure fluctuations increases with both excess gas velocity and particle diameter. Svoboda et al. (1983) also reported that the amplitude of pressure fluctuations depends upon the height above the distributor. Pressure fluctuations can be very different at different locations on the axis of the bed (the region of bubble coalescence is displaced as the gas velocity increases) and thus the position at which pressure fluctuations are measured becomes an important factor in determining the relationship between the standard deviation of pressure fluctuations and the gas velocity. The effect of the probe location was studied by Hong et al. (1990) and Wilkinson (1995) for several particle sizes and static bed heights. The use of absolute or differential probes has also been discussed in order to elucidate weather or not they provide similar or different information: Roy and Davidson (1989) showed that single point pressure measurements were different from differential pressure measurements because the former included contributions from all 0263-8762/$ -see front matter

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Section: Introductionmentioning

confidence: 93%

Standard deviation of absolute and differential pressure fluctuations in fluidized beds of group B particles

Sobrino

Sánchez-Delgado

García-Hernando

et al. 2008

Chemical Engineering Research and Design

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“…Larger natural frequencies than the zero frequency give rise to the number of nodes. As shown in Figure 1, some damping effects are included in f 0 , as estimated according to (Verloop and Heertjes, 1974) as:…”

Section: The Acoustic Interaction Modelmentioning

confidence: 99%

“…Purely periodic oscillations of the gas pressure in gas-solid fluidized bed described by expressions analogous to eq.1 have been observed in shallow beds (Verloop and Heertjes, 1974). As noted in Hao and Bi (2005), the different dynamical forces acting within a freely fluidized bed (i.e.…”

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confidence: 94%

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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“…The first two researchers to present mechanisms for fluctuations were Hiby [9] and Verloop [10]. Fundamentally the mechanism proposed by both these researchers is the same,although the derivations differ slightly.…”

Section: Experimental Operating Conditionsmentioning

confidence: 99%