A numerical model of gas-fluidized beds

Abstract

A first-principles model for a gas-fluid&d bed based on the so-called "two-fluid model" (TFM) has been developed_ In the TFM approach, both phases are considered to be continuous and fully interpenetrating. The equations for mass, momentum and thermal energy conservation, supplemented with the necessary constitutive equations, have been sotved by a finite-difference technique on a mini-computer. The computer model calculates the porosity, the pressure, the fluid phase temperature, the solid phase temperature and the velocity fields of both phases in two-dimensional Cartesian or axi-symmetrical cylindrical coordinates. Contrary to previous modelling work, all important terms have been retained in the transport equations. As a test of the theoretical model, the phenomena associated with the formation, propagation and eruption of a single bubble in a cold-flow two-dimensional air-fluidized bed with one central orifice have been calculated theoretically. The calculation was done for mono-sized spherical solid particles with a diameter of 500 pm and a true density of 2640 kg/ma. Our preliminary calculations indicate strong leakage of bubble gas into the emulsion phase, especially during the initial stage of bubble formation. In its present state, the model does not correctly display all the details associated with the propagation of bubbles in gas-fluidized beds. The further development of the model, both from a physical (bed rheology) and mathematical (finite-difference approximations) point of view, Seems highly desirable.

Numerical Investigation on the Effect of Pressure on Fluidization in a 3D Fluidized Bed

“…17,18 To account for particle−particle interactions, the kinetic theory of granular flow 19,20 (KTGF) is used. In this work, the standard TFM equations were used to describe the continuum modeling approach for the gas and solids phases.…”

A Study of Vertical Gas Jets in a Bubbling Fluidized Bed

“…Measured gas and particle mean velocities in a bubbling bed using the robust technique developed in the previous quarter 4  Analyzed velocity profiles by checking for self-similar behavior  Validated the gas-solid equations in MFIX with experimental data from a bubble injection experiment performed by Kuipers (1990). 5  Measured mean velocity profiles by varying the fluidized state of the emulsion using the LDV technique.…”

“…Additional validations of the gas-solid equations used by MFIX were made by comparisons with the experimental data of Tsuji et al (1983) for vertical risers and Kuipers (1990) for bubble injection, and were found to match favorably. These are, however, not included in this report.…”

Mesoscale dynamic coupling of finite- and discrete-element methods for fluid–particle interactions

“…For the past two decades, particulate flows have been an active area of research and two widely used approaches are now considered state of the art. The first approach is based on an Eulerian continuum model of two phase flows, which only describes the averaged behaviour of the multi-phase media [1]. The second approach is based on an Eulerian-Lagrangian approach using finite-volume/finite-difference methods on a fixed grid as a fluid solver and either an immersed boundary [2], fictitious domain (FD) [3], marker and cell [4] or discrete-element method (DEM) [5] for the particles.…”