Shear efficiency

For highly viscous blends, the mixer needs to have a higher shear efficiency or to be heated at higher temperatures. In this case, the energy consumption is close to 100 kJ kg . Mixing or pulverization of pigments needs machines equipped with a friction blade mixing powders with liquids is done in turbomixers (Fig. 14.6). 

To minimize the self-weight-induced stresses, innovative deck cross-sections with high sectional (bending and shear) efficiencies coupled with innovative materials have to be invented A few such cross-sectional shapes of FRP composite decking were successfully implemented by various State Departments of Transportation in the United States. The decking systems are shown in Fig. 31.3, with cost comparisons in Table 31.1. 

In common with the thermal processes (Section 4.3), these processes and mechanical processes that use chemical agents (Section 4.4) often use supercritical fluids (e.g., supercritical CO2) as a process aid. A supercritical fluid is chosen that is compatible with the rubber that is being devulcanised so that it swells the rubber within the process equipment and so facilitates devulcanisation by ensuring a high degree of fill and, hence, shearing efficiency. It is, however, harder to maintain the fluid in a supercritical state in these types of processes, due to leakage and loss of pressure, than in sealed vessels (e.g., autoclaves), as are often used in thermal processes. 

Rotary cell culture systems 36 X 10 cells/mL Low shear, efficient gas and nutrient transport Aggregation, less scalable than stirred vessels Come et al. (2008) Gerecht-Nir et al. (2004)... 

Newtonian behavior the rate of shear is small compared to the rate constant for the flow process. When molecular displacements occur very much faster than the rate of shear (7 < kj ), the molecules show maximum efficiency in dissipating the applied forces. When the molecules cannot move fast enough to keep pace with the external forces, they couple with and dissipate those forces to a lesser extent. Thus there is a decrease in viscosity from its upper, Newtonian limit with increasing 7/kj. The rate constant for the flow process is therefore seen to define a standard against which the rate of shear is to be judged large or small. In the next section we shall consider a molecular model in terms of which this rate constant can be analyzed. 

Minimization of the elastic behavior of the fluid at high deformation rates that are present when high molecular weight water-soluble polymers are used to obtain cost-efficient viscosities at low shear rates. 

Drops coalesce because of coUisions and drainage of Hquid trapped between colliding drops. Therefore, coalescence frequency can be defined as the product of coUision frequency and efficiency per coUision. The coUision frequency depends on number of drops and flow parameters such as shear rate and fluid forces. The coUision efficiency is a function of Hquid drainage rate, surface forces, and attractive forces such as van der Waal s. Because dispersed phase drop size depends on physical properties which are sometimes difficult to measure, it becomes necessary to carry out laboratory experiments to define the process mixing requirements. A suitable mixing system can then be designed based on satisfying these requirements. 

Off-Gas Treatment. Before the advent of the shear, the gases released from the spent fuel were mixed with the entire dissolver off-gas flow. Newer shear designs contain the fission gases and provide the opportunity for more efficient treatment. The gaseous fission products krypton and xenon are chemically inert and are released into the off-gas system as soon as the fuel cladding is breached. Efficient recovery of these isotopes requires capture at the point of release, before dilution with large quantities of air. Two processes have been developed, a cryogenic distillation and a Freon absorption. 

Disk Pumps. When pumping shear-sensitive or highly viscous fluids, it is desirable to reduce internal turbulence caused by the vanes. The disk pump design rehes on the centrifugal frictional effect of a vaneless disk. Whereas the efficiency of this pump is lower than that of similar centrifugal pumps having vanes, it is often the only solution to certain pumping appHcations. 

Anodic deposition is controlled by either fluid shear (cross-flow filtration) (48), similar to gel-polarization control, or by continual anode replacement (electrodeposited paints) (46). High fluid shear rates can cause deviations from theory when E > (49). The EUF efficiency drops rapidly... 

In the equation referred to above, it is assumed that there is 100 percent transmission of the shear rate in the shear stress. However, with the slurry viscosity determined essentially by the properties of the slurry, at high concentrations of slurries there is a shppage factor. Internal motion of particles in the fluids over and around each other can reduce the effective transmission of viscosity efficiencies from 100 percent to as low as 30 percent. 

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