Hydrodynamics of Fluidization of Mixtures

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Abstract CTS-9610053 Quantitative understanding of the hydrodynamics of fluidization is needed for the design and scale-up of efficient new reactors in the oil, chemical, and electric power industries. The objective of this research is to extend the development of the hydrodynamic theory of fluidization and multiphase flow. This theory uses the principles of conservation of mass, momentum and energy for each phase and particle size. While the conservation laws are well known and accepted, relatively little has been done theoretically and experimentally to determine the constitutive equations for a mixture of different particle sizes that are needed as an input into various computational fluid dynamics (CFD) codes. The recently developed theory of granular flow, as reviewed by Gidaspow in Multiphase Flow and Fluidization, Academic Press, 1994, gave us a different perspective on the subject. During the last three years much experimental evidence was gathered that shows that indeed the particles in a fluid behave as another phase with their own pressure, granular temperature, viscosity, etc. In the dilute limit the particles obey an ideal "gas" equation of state. For denser flow of 75 micron fluidized catalytic cracking catalyst particles, the standard hard sphere model for a cohesive pressure was corrected. Cohesion was independently determined using radial distribution functions measured using a charge coupled device (CCD) camera. These experiments will be repeated for larger particles with negligible cohesion. Then this theory will be extended to a mixture of binary sizes, where the principle of equi-partition does not apply. Measurements will be made of particle velocities, concentrations and radial distribution functions using the newly developed CCD camera method and more conventional techniques, such as X-ray densitometers, in a two-story circulating fluidized bed (CFB) in a liquid-solid loop and in a gas-liquid-solid rectangular fluidized bed. These measurements will give th e viscosities of the mixtures. The measured velocity, particle concentration and turbulence (granular temperature) profiles will be compared to the CFD computations using the computer code.