Kwauk proposed that the characteristic fine particle distribution in fast fluidization could not be accounted for by the one-dimensional analysis on accelerative motion of particulate fluidization, and presented a physical model for a gas-solid fast fluidization system. The average solid concentration is composed of both the strands and dilute continuum. Besides, he explained that characteristically the curve extends from a low voidage at the bottom.
The random particle motion phenomena in a fluidized bed is similar to the ecological diffusion process in which motion is from high particle concentration to lower concentration. Combining Brownian movement model and random walk theory with particle motion in a fast-fluidized bed.
[...] The core-annulus assumption has become the basic for many models. The flow structure can be visualized as shown in Figure 2. Figure Flow structure in Fast Fluidized Bed The particles, which are coming down in the annular region is coming with a velocity that is modeled in this work. The gas flows upward in the core only. Here, the assumptions are The slip velocity in the core is equal to the terminal settling velocity of the average particle. The annular voidage is equal to minimum fluidization voidage of the particles. [...]
[...] From a mass balance across a typical section of the riser, the upward flux E can also be evaluated as ( G is the net solids flux or circulation rate and W is the downward solids flux, which is limited to the annular region and voidage in the annular region is assumed to be that of a fluidized bed at minimum fluidization condition The downward flux, can be calculated from ( ( ( ( The upward particle mass flow rate can be calculated along the core region as ( Calculation of Entrainment Flux: For calculating the solid circulation rate at different heights we need to calculate entrainment flux and down ward flux at that heights. [...]
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