The Development and Impact of Instabilities in Gas Fluidized Beds PDF Download

Author: Jayati Johri
Publisher:
ISBN:
Category :
Languages : en
Pages : 382

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Author: Xue Liu
Publisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages :

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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 113

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This project studies the particle pressure, which may be thought of as the force exerted by the particulate phase of a multiphase mixture, independently of that exerted by other phases. The project is divided into two parts, one concerning gas and the other liquid fluidized beds. Previous work on gas fluidized beds had suggested that the particle pressures are generated by bubbling action. Thus, for these gas fluidized bed studies, the particle pressure is measured around single bubbles generated in 2-D fluidized beds, using special probes developed especially for this purpose. Liquid beds are immune from bubbling and the particle pressures proved too small to measure directly. However, the major interest in particle pressures in liquid beds lies in their stabilizing effect that arises from the effective elasticity (the derivative of the particle pressure with respect to the void fraction), they impart to the bed. So rather than directly measure the particle pressure, the authors inferred the values of the elasticity from measurements of instability growth in liquid beds; the inference was made by first developing a generic stability model (one with all the normally modeled coefficients left undetermined) and then working backwards to determine the unknown coefficients, including the elasticity.

Author: Kevin Matthew Mandich
Publisher:
ISBN: 9781303194337
Category :
Languages : en
Pages : 138

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Applied mathematical techniques are employed to investigate the hydrodynamic stability of three gas-fluidized bed problems. The first considers an unbounded bed subjected to a uniform fluid-phase pressure drop. The dispersion relation is solved numerically to determine the stability characteristics as a function of the bed parameters. Analytic solutions are derived for the cases of purely transverse and purely longitudinal disturbances. Long-wavelength analyses performed on each reveal the relevant stability mechanisms. Several of these are novel mechanisms stemming from the extension of kinetic gas theory to rapid granular flows used to close the equations of motion. The linear stability analysis is then applied to two bounded problems: a cylindrically-bound vertical bed and a planar bed whose bounding walls are inclined from the vertical. The base states and linear stability analyses for both problems are solved numerically to determine the complex frequency. In the 3D vertical bed, no particle movement is allowed in the base state, while this restriction is relaxed for the 2D inclined bed to allow for the non-uniform solid-phase pressure distribution. It is found that the axisymmetric disturbance is dominant in the cylindrical bed. The dependence of its growth rate on the particle diameter and density matches previously-published tendencies for a gas-fluidized bed to exhibit bubbling at minimum fluidization as a function of these parameters. At low angles of inclination [theta], the eigenmodes of the inclined bed and their characteristics exhibit similar behavior to those of the cylindrical bed. Analytic solutions derived for the limiting cases of full slip at the walls for both beds explain these similarities. The dominant mode of the inclined bed at large [theta] exhibits an eigenmode whose time-evolution yields regions of drastic voidage adjacent to the top wall, matching the development and propagation of bubbles observed in experiment. Pressure time signals were obtained during experiments performed on lab-scale vertical and inclined beds. A Fourier analysis yielded dominant experimental frequencies, which were compared to those from the numerical methods. The frequencies as a function of fluidization velocity and [theta] show qualitatively similar behavior between the stability analysis and experimental observations.

Author: Roy Jackson
Publisher: Cambridge University Press
ISBN: 9780521781220
Category : Mathematics
Languages : en
Pages : 358

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This 2000 book provides a careful and critical development of the equations which describe the motion of fluid-particle mixtures.

Author: Xue Liu
Publisher:
ISBN: 9781109876369
Category : Gas flow
Languages : en
Pages : 287

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Finally, we extend our work to investigate the steady state solutions of boundary-driven and body-force-driven granular flows and gas-particle fluidized beds with a bi-disperse particle mixture. Granular energy equipartition breaks down with an increase in the system inelasticity and the mass ratio, whereas the effect of the size ratio is very small if the two particle species have the same mass. The segregation of total particles and each individual particle species is enhanced when the effect of non-equipartition of granular energy is considered. The species segregation is enhanced with a decrease in the system elasticity, an increase in the average solids fraction or an increase in the size ratio, due to the competition of three diffusion forces: the thermal diffusion force, the ordinary diffusion force and the pressure diffusion force. For gas-particle fluidized beds and granular flows in a channel, we find that for the kinetic theory models used in the present study, the solids fraction and the granular temperature profiles are quite similar.

Author: K. S. Sutherland
Publisher:
ISBN:
Category : Bulk solids flow
Languages : en
Pages : 58

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The development of a continuous method for determining changes in particle size and particle size distribution in fluid-bed systems has been studied experimentally. Differential pressure measurements were employed to study the effects of solid particle size on the behavior of gas-fluidized beds. The relevant bed properties are briefly described and a review given of previous work on the study of fluidized-bed quality. It is shown that, within certain limitations, measurements of bed quality can be used to indicate changes in particle size. Gas-bubble velocities, while increasing in proportion to the square root of bubble diameter, are also shown to be dependent on particle size, increasing as the particle size decreases.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 29

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Campbell and Wang (1991) showed that the particle pressures in gas-fluidized beds were largely generated by the passage of bubbles. In particular, they showed that the average particle pressure exerted on the side walls scaled with the average size of the bubble. This immediately brings to mind two questions: (1) what is it about bubbles that leads to particle pressure generation and (2) would there be measurable particle pressures in liquid-fluidized beds which, while unstable, do not bubble? This project is largely aimed at answering these two questions. To attack the first problem, the authors have built a two-dimensional gas-fluidized bed into which bubbles may be injected and the distribution of particle-pressure measured. For the latter, other experiments are being performed in liquid fluidized beds. However, it soon became apparent that the particle pressures generated in the liquid beds are extremely small. This has pointed that phase of the research in two directions. The first is the design and construction of a third, and more sensitive, from of the particle pressure transducer. The second approach arose from reflection on what ultimately was the utility of the current research. This led to the development of a generic stability model, in which all modeled terms are left unspecified. From analyzing this model, they have developed an experimental plan that, by measuring the characteristics of voidage disturbances and comparing with the theory, will allow them to back out appropriate values for the modeled terms. The results will not only yield insight into the particle pressure, but also of the fluid drag. The latter results may be used to evaluate common models for these terms.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 39

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Book Description
Campbell and Wang (1991) showed that the particle pressures in gas-fluidized beds were largely generated by the passage of bubbles. In particular, they showed that the average particle pressure exerted on the side walls scaled with the average size of the bubble. This immediately brings to mind two questions: (1) what is it about bubbles that leads to particle pressure generation and (2) would there be measurable particle pressures in liquid-fluidized beds which, while unstable, do not bubble? This project is largely aimed at answering these two questions. To attack the first problem, the authors have built a two-dimensional gas-fluidized bed into which bubbles may be injected and the distribution of particle-pressure measured. For the latter, other experiments are being performed in liquid fluidized beds. However, it soon became apparent that the particle pressures generated in the liquid beds are extremely small. This has pointed that phase of the research in two directions. The first is the design and construction of a third, and more sensitive, from of the particle pressure transducer. The second approach arose from reflection on what ultimately was the utility of the current research. This led to the development of a generic stability model, in which all modeled terms are left unspecified. From analyzing this model, they have developed an experimental plan that, by measuring the characteristics of voidage disturbances and comparing with the theory, will allow them to back out appropriate values for the modeled terms. The results will not only yield insight into the particle pressure, but also of the fluid drag. The latter results may be used to evaluate common models for these terms.

Author: John R. Grace
Publisher: John Wiley & Sons
ISBN: 3527340645
Category : Technology & Engineering
Languages : en
Pages : 626

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Book Description
A concise and clear treatment of the fundamentals of fluidization, with a view to its applications in the process and energy industries.