Flow regime very dilute

However, it is not always easy to distinguish between the flow behavior encountered in the fast fluidization and the transport bed reactors [56]. The transport reactors are sometimes called dilute riser (transport) reactors because they are operated at very low solids mass fluxes. The dense riser transport reactors are operated in the fast fluidization regime with higher solids mass fluxes. The transition between these two flow regimes appears to be gradual rather than abrupt. However, fast fluidization generally applies to a higher overall suspension density (typically 2 to 15% by volume solids) and to a situation wherein the flow continues to develop over virtually the entire... 

For gas-particle flows, fhe mosf obvious manifestation of non-equilibrium behavior is particle trajectory crossing (PTC) at KUp = oo (i.e. no collisions). PTC occurs in the very-dilute-flow regime ( p c 1) and is most easily identified when fhe granular femper-afure is null (Map = c ). An example of PTC is shown in Figure 1.4. The panel on fhe... 

By means of Eqs. (83) and (79) for a constant density binary of different particle sizes, and Eqs. (110) and (107) for a fixed size binary of different particle densities, Table 2 indicates what happens to the nondimensionalized bulk density difference in each case as one moves from a very dilute system (e.g., Sg = 1 = 8,) to a very dense system (e.g. 8g = 0.5 = s,). It is seen that, irrespective of flow regime, y decreases as s decreases, while Yi, does the reverse. This tendency by y was already rationalized in the discussion (item 2) of Eq. (84). Substituting Eq. (110) into Eq. (107), we obtain... 

Such a flow is not encountered, except in laminar regimes of very dilute concentrations... 

Suppression of domain coalescence in the melt flow regime is one of the most important effects of the interfacial reaction on morphology and morphology development. Simdararaj and Macosko [33] have conducted a careful study of morphology as a function of dispersed phase voliune fraction in reactive and non-reactive blends to discern the influence of the reaction. Figure 5.9 illustrates the dependence of the dispersed phase domain size on the dispersed phase concentration for typical uncompatibilized blends. At dispersed phase concentrations less than about 0.5 wt.% the system is dilute enough that coalescence is insignificant due to the very low frequency of dispersed phase domain... 

From Figure 23.12, we can see that in spite of using a high space velocity and catalyst bed diluted, the sample showed a very high conversion in the first hour and drops considerably after some time of reaction, stabilizing it at around 10%. After 48 h of reaction, the flow was increased and the conversion decreased proportionally. This suggests that the system operated in the kinetic regime, i.e., in the absence of diffusion effects in a differential reactor. 

The hydrodynamics of a circulating fluidized bed is further complicated by the existence of significant variations in solids concentration and velocity in the radial direction. A more uniform distribution can be achieved at conditions of lower solids concentrations under higher gas flow conditions. In the dilute transport regime, the solids concentration is very low and both gas and solids have short residence times. 

---