Hydrodynamics of Fluidization of Mixtures

摘要CTS-9610053对流态化流体力学的定量了解是石油、化工和电力工业中高效新型反应堆的设计和放大所必需的。本研究的目的是拓展流态化和多相流流体力学理论的发展。这一理论使用质量守恒、动量守恒和能量守恒原理来描述每个相态和颗粒的大小。虽然守恒定律是众所周知和被接受的，但在理论和实验上确定不同颗粒尺寸混合物的本构方程的工作相对较少，这些本构方程是各种计算流体动力学(CFD)程序的输入。Gidaspow在《多相流和流态化》一书中回顾了最近发展起来的颗粒流理论，学术出版社，1994年，它给了我们一个不同的视角。在过去的三年中，收集了大量的实验证据，表明流体中的颗粒确实表现为另一种相，具有它们自己的压力、颗粒温度、粘度等。在稀释极限中，颗粒服从理想的“气体”状态方程。对于75微米流态化催化裂化催化剂颗粒的更密集流动，修正了凝聚压力的标准硬球模型。粘聚力是通过使用电荷耦合器件(CCD)相机测量的径向分布函数独立确定的。对于凝聚力可以忽略不计的较大粒子，这些实验将重复进行。然后，这一理论将被扩展到二进制大小的混合，其中等分原理不适用。将使用新开发的CCD摄像方法和更传统的技术，如X射线密度计，在液固循环的两层循环床(CFB)和气液固矩形沸腾床中测量颗粒速度、浓度和径向分布函数。这些测量将给出混合物的粘度。测量的速度、颗粒浓度和湍流(颗粒温度)分布将与使用计算机代码的CFD计算进行比较。

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.