Chaotic and statistical tests on fiber optic dynamic data taken from the riser section of a circulating fluidized bed

Numerical simulations using the Gidaspow and Syamlal-O’Brien drag models have been performed based on the National Energy Technology Laboratory small scale challenge problem for three test cases. Validation tools including statistical moments, spectral analysis, and the autocorrelation function are used to analyze the pressure drop fluctuations. The analyses using these tools reveal a regime change from bubbling/slugging to turbulent flow with increasing superficial gas velocity. 1D discrete wavelet analysis is utilized in the study of the distribution of energy between the macro-, meso-, and microscales and also in the characterization of turbulence quantified in terms of the flatness factor. 1D fast Fourier transform energy spectra are constructed from the predicted and measured particle velocity data and compared. Predicted and measured granular temperatures are found to be in reasonable agreement with literature values.

Section: Results and Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Two-Fluid Model Simulations of the National Energy Technology Laboratory Bubbling Fluidized Bed Challenge Problem

Lungu

Wang

Yang

et al. 2016

“…Yan et al 25 tried to identify the clusters in the riser by combing wavelet decomposition with sensitivity analysis method. Breault et al 26 decomposed the raw voltage signal through discrete wavelet decomposition and proposed d3−d5 characterizes the mesoscale. However, these methods do not give more information about size distribution and velocities of mesoscale flow structures.…”

Section: Introductionmentioning

confidence: 99%

Identification of Mesoscale Flow in a Bubbling and Turbulent Gas–Solid Fluidized Bed

Niu

Huang

Chu

et al. 2019

Based on the moment consistency principle, the bubble threshold was determined by using the traversing method. A novel approach was proposed to identify bubbles and agglomerates from transient signals registered in a cold mode fluidized bed dealing with different particles. Bubble and agglomerate hydrodynamics including volume fraction, solid holdup, immigration velocity, and frequency were investigated. Adding fine powder promotes the formation of particle agglomerates at low superficial gas velocity and leads to a great bubble volume fraction at high superficial gas velocity. Bubble frequency increases significantly during the flow pattern transition from bubbling to turbulence bed. Compared with FCC particles, the mixed particles have a narrow bubble chord length distribution. The net velocity of agglomerates is positive in the center and close to zero or even negative in the vicinity of the wall. The agglomerate frequency in the mixed particle bed is significantly lower than that in the FCC particle bed.

“…Up to now, numerous studies have been conducted to measure the distributions of the time-average particle velocity and time-average solids flux in CFB risers. The devices employed include laser Doppler velocimetry, − an optical fiber probe, ,, and particle image velocimetry. − A consensus has already been reached on many points: (1) time-average particle velocity increases from the riser wall to riser center; (2) time-average particle velocity may be negative in the riser wall; (3) time-average particle velocity increases with both superficial gas velocity and solids circulating rate; (4) time-average solids flux increases from the riser wall toward the riser center; and (5) time-average solids flux may be negative in the riser wall.…”

Section: Introductionmentioning

confidence: 99%

Tracking the Flow Dynamics in Circulating Fluidized Bed through High-Speed Photography

Wei

Zhu

2019

In gas−solid circulating fluidized beds, particle velocity and solids flux are crucial parameters for understanding the gas−solid interaction. In the literature, the time-average information has been investigated intensely, but the analysis of instantaneous information remains lacking. In this work, flow behavior in a narrow rectangular circulating fluidized bed has been recorded using a high-speed camera. Then, with a verified correlation between grayscale and solids holdup, particle velocity is computed by tracking local solids holdup characteristics using a two-dimensional cross-correlation, and solids flux is computed by multiplying the particle velocity with particle density and local solids holdup. The time-average information in this work is found to be consistent with that of previous publications. Instantaneous information of particle velocity and solids flux, including relations with local solids holdup, instantaneous radial distributions, instantaneous solids circulating rates, and impacts of macro-fluctuation is analyzed systematically and discussed in detail for the first time.