Measuring bubble, drop and particle sizes in multiphase systems with ultrasound

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.

Section: Introductionmentioning

confidence: 99%

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

Briongos

Sobrino

Gómez-Hernández

et al. 2013

“…Those acoustic techniques are later applied as active or as passive methods (Cents et al, 2004;Herrera et al, 2002;Boyd and Varley, 2002). With regard to the passive acoustic emission in which the signal collected is created by the fluidizing process itself, acoustics measurements have been reported by either placing the sensor inside (Zukowski, 2001) or outside the vessel (Briongos et al, 2006b;Cody et al, 1996;Finney et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

Can low frequency accelerometry replace pressure measurements for monitoring gas-solid fluidized beds?

Martín

Briongos

Aragón

et al. 2010

a b s t r a c tThis paper is addressed to introduce a methodology based on low frequency accelerometry that can be used for gas solid fluidized bed monitoring, and for dynamic diagnosis purposes. The proposed methodology consists on extracting the low frequency information encoded within an accelerometry signal, by means of the Hilbert transform method. The time and the frequency domain analysis show how this low frequency information is directly related to the conventional pressure fluctuation measurements, providing useful information on bulk and bubble dynamics. The cross correlation and the coherence function analysis between the pressure and the envelope process of the measured accelerometer signals ''E'', exhibit values approaching unity for frequencies ranging between 2 and 4 Hz. This reveals that pressure signals and accelerometry envelope are related processes. The results from the Coherent Output Power, COP, and the Incoherent Output Power, IOP, analysis confirms that both pressure and envelope time series exhibit the same global and local features open the possibility of using low frequency accelerometers instead of conventional pressure transducers for monitoring and for dynamic diagnosis purposes.

“…The mass transfer parameters are a function of the local prevailing hydrodynamics (Cents et al, 2003), which in its turn are affected by the bubble behavior and variation of physical properties due to inhomogeneous chemical species distributions. It is these complex interactions that makes the overall prediction of performance and scale-up of this type of reactor very difficult.…”

Section: Introductionmentioning

confidence: 99%

Detailed modeling of hydrodynamics, mass transfer and chemical reactions in a bubble column using a discrete bubble model

Darmana

Deen

Kuipers

2005

167

197

A 3D discrete bubble model is adopted to investigate complex behavior involving hydrodynamics, mass transfer and chemical reactions in a gas-liquid bubble column reactor. In this model a continuum description is adopted for the liquid phase and additionally each individual bubble is tracked in a Lagrangian framework, while accounting for bubble-bubble and bubble-wall interactions via an encounter model. The mass transfer rate is calculated for each individual bubble using a surface renewal model accounting for the instantaneous and local properties of the liquid phase in its vicinity. The distributions in space of chemical species residing in the liquid phase are computed from the coupled species balances considering the mass transfer from bubbles and reactions between the species. The model has been applied to simulate chemisorption of CO 2 bubbles in NaOH solutions. Our results show that apart from hydrodynamics behavior, the model is able to predict the bubble size distribution as well as temporal and spatial variations of each chemical species involved.