Dispersions radial

Below a critical power input the gas bubbles are not affected laterally but move upward with their natural buoyancy. This condition is called gas flooding of the impeller. At higher power inputs the gas is dispersed radially, bubbles impinge on the walls and are broken up, consequently with improvement of mass transfer. A correlation of the critical power input is shown as Figure 10.10. 

Centrifugal separation of gas, oil, water and solid phases, making the dispersion radially inhomogeneous, and possibly breaking emulsions or collapsing foams. 

Like axial dispersion, radial dispersion can also occur. Radial-dispersion effects normally arise from radial thermal gradients that can dramatically alter the reaction rate across the diameter of the reactor. Radial dispersion can be described in an analogous manner to axial dispersion. That is, there is a radial dispersion coefficient. A complete material balance for a transient tubular reactor could look like ... 

In upflow bubble operation the consumption of the gas phase by reaction must also be considered in the model if the reactor operates under lower pressure (<20 bar) and if the reactor length is of technical dimensions (L>2 m) additionally gas phase dispersion (radial and axial) may have an influence on conversion [65]. As this reactor type is also used in waste water treatment as well as in fermentation processes, the possible non-Newtonian behavior of the liquid phase as well as the coalescence behavior of the system must be taken into account. Finally, it should be remembered that - comparable to fluidized bed reactors - results from laboratory reactors with small column diameter and/or particle sizes smaller than 0.2 cm usually cannot be regarded as representative for technical upflow units, because capillary force as well as lare scale circulation in the liquid phase may be significantly different. 

D Riser diameter Axial dispersion Radial dispersion Diffusion... 

Fluid heat dispersion (axial) Fluid heat dispersion (radial) Solid heat dispersion (axial) Solid heat dispersion (radial) Fluid-solid mass transfer... 

The mass balance in the void space of the column is described by a plug flow model with axial dispersion radial gradients are neglected due to convection enforced in axial direction ... 

When the solid particles enter near the cylindrical wall they can be dispersed radially inwards because of the intensive turbulent mixing in the feed sections. There is, however, very little information about the behaviour of the liquid in the cylindrical section this portion of the cyclone is usually treated as a preliminary separating zone and the main separations are thought to be performed in the conical section. 

Diffusion limitations inside the catalyst neglected Plug flow or axial dispersion neither radial concentration nor temperature gradients in the reactor Plug flow or axial dispersion radial concentration and temperature gradients in the reactor... 

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