Internal mixing

Atomizers for large boiler burners are usually of the swid pressure jet or internally mixed twin-fluid types, producing hoUow conical sprays. Less common are the externally mixed twin-fluid types (89,90). 

Internal mixing is widely used with fluorocarbon elastomers. Gumstocks and compounds that are particularly successful fall in the viscosity ranges discussed earlier, and use both incorporated bisphenol-type and peroxide cure systems. A typical internal mix cycle mns 6—8 min with a drop temperature of 90—120°C. The typical formulations in Tables 4 and 7 are readily mixed in an internal mixer. 

However, the static-drop assumption is usually extremely conservative. For example, the high interfacial velocity in the spray from nozzles yields a high degree of internal mixing and much higher transfer. 

The second use of Equations (2.36) is to eliminate some of the composition variables from rate expressions. For example, 0i-A(a,b) can be converted to i A a) if Equation (2.36) can be applied to each and every point in the reactor. Reactors for which this is possible are said to preserve local stoichiometry. This does not apply to real reactors if there are internal mixing or separation processes, such as molecular diffusion, that distinguish between types of molecules. Neither does it apply to multiple reactions, although this restriction can be relaxed through use of the reaction coordinate method described in the next section. 

The design equations for a chemical reactor contain several parameters that are functions of temperature. Equation (7.17) applies to a nonisothermal batch reactor and is exemplary of the physical property variations that can be important even for ideal reactors. Note that the word ideal has three uses in this chapter. In connection with reactors, ideal refers to the quality of mixing in the vessel. Ideal batch reactors and CSTRs have perfect internal mixing. Ideal PFRs are perfectly mixed in the radial direction and have no mixing in the axial direction. These ideal reactors may be nonisothermal and may have physical properties that vary with temperature, pressure, and composition. 

The lithium abundance, using the Li I 6707 doublet, will be used as a signature of internal mixing to confirm whether or not internal mixing is one of the mechanisms responsible for the existence of blue straggler stars. 

The formation mechanisms that can explain the existence of blue stragglers are still very unclear. The different explanations involve mass-transfer in binary systems, or internal mixing. 

For Wolf-Rayet stars of type WN, rotation makes smoother changes of abundances, due to internal mixing. For WN stars, the transition phase, with still H present, becomes longer due to rotation and this increases the late WN phase (WNL) where H is usually present. The CNO abundances at the end of the WN phase are the same for rotating and non-rotating models, because they are model independent and determined just by CNO nuclear equilibrium. Indeed, CNO abundances in WN stars provide a unique test of the physics of the CNO cycle. 

Ten years after the first ESO Workshop on light elements, and five years after the IAU in conference in Natal (Brazil) on the same subject, we felt that it was time to have a new conference on this topic a wealth of new observational data have become available from the 8-meter telescopes and in particular from the VLT, and, at the same time, in the last years new theoretical roads have also been inaugurated in the interpretation of the stellar data. It soon became clear, on the other hand, that in order to understand the evolution of the fragile Li and Be in stars and in the Galaxy, the whole problem of internal mixing in stars must be addressed and understood first, and therefore a large number of elements must be investigated, in many different environments. 

The disc holder was machined to fit into the stainless steel flange in such a way that it directs the gas to consecutively sweep both faces of the catalyst disc, with an expansion volume in-between. This configuration provided good gas-phase mixing in the cell, thus allowing the reactor to be characterized as a CSTR. This mode of internal mixing eliminates the need for internal moving parts or external recycle loops and pumps. 

Figure 2.6. Schematic of internal-mixing two-fluid atomizers.

A variety of atomizer designs have been developed in an effort to control the droplet size distribution and to increase the yield of fine powders. Gas atomizers used for the atomization of melts may be loosely classified into two primary categories in terms of the interaction mode between a liquid metal and an atomization gas during atomization, i.e., (1) internal mixing and (2) external mixing. 

In internal mixing atomization (for example centrifugal-pneumatic atomization), 159] the liquid metal and gas enter the swirl jet atomizer tangentially under pressure (Fig. 2.13)J159] The two fluids rotate, form a mixture, and accelerate in the confuser. Due to the strong centrifugal force, the liquid metal forms a film at the nozzle exit even without the presence of the gas. With the applied gas, the liquid film is atomized into a fine dispersion of droplets outside the nozzle. 

Figure 2.13. Schematic of an internal-mixing atomizer for atomization of melts.

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