Power high viscosity system

From a practical point of view, power consumption is perhaps the most important parameter in the design of stirred vessels. Because of the very different flow patterns and mixing mechanisms involved, it is convenient to consider power consumption in low and high viscosity systems separately. 

A standard baffle configuration consists of four vertical plates having width equal to 8 to 10% (T/12 to T/10) of the tank diameter. Narrower baffles are sometimes used for high viscosity systems, buoyant particle entrainment (width = 2% of T), or when a small vortex is desired. A small spacing between baffles and the tank wall (1.5% of T) is allowed to minimize dead zones particularly in solid-liquid systems. Wall baffles increase the power consumption of the mixer and generally enhance the process result. 

The shape of the fuel spray is related to viscosity. High viscosities cause poor atomization and a solid-stream jet spray pattern. Poor combustion and low power result. Low viscosities result in soft, nonpenetrating fuel spray, leakage of fuel past the injection plunger, and possible wear of fuel system components. 

The volumetric gas-liquid mass transfer coefficient, khaL, largely depends on power per unit volume, gas velocity (for a gassed system), and the physical properties of the fluids. For high-viscosity fluids, kLaL is a strong function of liquid viscosity, and for low-viscosity fluids (fi < 50 mPa s), kLaL depends on the coalescence nature of the bubbles. In the aeration of low-viscosity, pure liquids such as water, methanol, or acetone, a stable bubble diameter of 3-5 mm results, irrespective of the type of the gas distributor. This state is reached immediately after the tiny primary bubbles leave the area of high shear forces. The generation of fine primary gas bubbles in pure liquids is therefore uneconomical. 

In this chapter, PEC systems using RTILs were introduced. The discussion focused on the relationship between the viscosity of the RTILs and the short-circuit photocurrent. It was shown that a Grotthus-like mechanism observed in a high concentration of iodide/triiodide redox in RTILs compensates for the shortcomings of the relatively high viscosity of RTILs. This is a critical fact for the apphcation of RTILs in actual electrochemical power devices. 

The drive system consists of a motor, a speed reducer, and thrust bearing (Figure 14-5). Obviously, the motor turns the screw and is often fairly large, as it takes a lot of power to push high viscosity molten poly-... 

Cabaret et al. (2008) and Gagnon et al. (1998) concluded that better mixing and higher product conversion can be achieved if a close clearance impeller, such as the helical ribbon, is used in conjunction with a radial flow impeller such as the RT in a highly viscous system. The Rushton-type turbine provides proper gas dispersion, while the close clearance impeller attempts to contact most of the reactor volume and provides proper bulk mixing, shear distribution, lower apparent viscosity, and minimal stagnant zones (Tecante and Choplin, 1993). These effects also lead to higher reactor utilization and can decrease power requirements. 

Countercurrent chromatography is based on the distribution of substances in two liquid phases [128,129]. The liquid is fed into a coiled tube that is moved along an orbital trajectory. Due to centrifugal power, the liquids move in a counter-current. For proteins and many other biomolecules, this method is not practical because of denaturation in a nonaqueous phase. In aqueous two-phase systems, at least one phase exhibits high viscosity and, therefore, mass transfer between the two phases is limited. Similar problems occur with reversed micelle extraction as were observed with the aqueous two-phase extraction [130]. CCC has not been used for large-scale purification of proteins and other biopolymers. 

In a single-phase system there are usually less transport limitations, resulting in a higher productivity per unit volume. This is particularly true when the liquid has a relatively high viscosity, since the dispersion of a gas in a viscous liquid is mostly not very effective. However, reaction in viscous liquids requires powerful agitation, in order to minimize transport limitations. 

Several attempts have also been made to destroy high-viscosity foams in the food industry (e.g. sugar and molasses), but unfortunately with these highly stabilized systems, the success rate is much lower. However, for the case of particle-stabilized foams (i.e. in the mineral industry, e.g. clays and carbonates) some degree of success has been achieved. Preliminary studies carried out by Sandor and Stein (18) clearly indicate that ultrasonic vibrations can both prevent the formation of foams and destroy foams stabilized with SDS surfactant and that those vibrators, which give the higher power consumption are more effective. It was also shown that the power consumption could be greatly enhanced when a broader tip was used. 

Countercurrent extraction should be the answer to the problem and has indeed been suggested by a number of authors [18-20]. Calculations by Englert and Tompa [21] have demonstrated that truly impressive results should be obtainable, provided some experimental problems could be solved. The latter relate to the extremely slow phase segregation caused by the high viscosity of the concentrated phase which is a handicap for continuous operation. Further, a binary solvent system in whieh the solvent power of the two phases is different, though not too much, is not easy to find. It has been a fairly reeent accomplishment of Wolf et al. [22 24] to overeome these practical problems and realize large-seale fractionation by continuous liquid liquid extraction. They included poly(isobutylene) in their studies and also sueeeeded in applying the method succesfully to linear poly(ethylene) [25]. 

A pressure stroke in the measuring kettle compresses the small nitrogen bubbles into tiny vesicles, so that the previous high viscosity rj results. Because of that, the stirring power increases by dpsa- The control system of the measuring kettle... 

Viscosity Glassifications. The general ISO iatemational viscosity classification system for iadustrial oils is given ia Table 4 from ASTM D2422 (American National Standard Z11.232). For high speed machines, ISO viscosity-grade 32 turbiae and hydrauHc oils are a common choice. ISO grades 68 and 100 are appHed for more load capacity ia slower speed machines where power loss and temperature rise are less of a question. 

Sodium is used as a heat-transfer medium in primary and secondary cooling loops of Hquid-metal fast-breeder power reactors (5,155—157). Low neutron cross section, short half-life of the radioisotopes produced, low corrosiveness, low density, low viscosity, low melting point, high boiling point, high thermal conductivity, and low pressure make sodium systems attractive for this appHcation (40). 

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