Low viscosity systems

Typical equipment for low viscosity liquids consists of a vertical cylindrical tank, with a height to diameter ratio of l.5 to 2, fitted with an agitator. For low viscosity liquids, high-speed propellers of diameter about one-third that of the vessel are suitable, running at 10-25 Hz. Although work on single-phase mixing of low viscosity liquids is of limited 

In equation 7.12, P is the impeller power, that is, the energy per unit time dissipated within the liquid. Clearly, the electrical power required to drive the motor will be greater than P on account of transmission losses in the gear box, motor, bearings, and so on. 

It is readily acknowledged that the functional relationship in equation 7.12 cannot be established from first principles. However, by using dimensional analysis, the number of variables can be reduced to give  

The simplest form of the function in equation 7.14 is a power law, giving  

The value of K depends on the type of impeller/vessel arrangement, and whether the tank is fitted with baffles. For marine-type three-bladed propellers with pitch equal to diameter, K has been found to have a value of about 41. 

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Emulsion Process. The emulsion polymerization process utilizes water as a continuous phase with the reactants suspended as microscopic particles. This low viscosity system allows facile mixing and heat transfer for control purposes. An emulsifier is generally employed to stabilize the water insoluble monomers and other reactants, and to prevent reactor fouling. With SAN the system is composed of water, monomers, chain-transfer agents for molecular weight control, emulsifiers, and initiators. Both batch and semibatch processes are employed. Copolymerization is normally carried out at 60 to 100°C to conversions of - 97%. Lower temperature polymerization can be achieved with redox-initiator systems (51). 

Fig. 4. Typical design elements foi wet deagglomeiation in low viscosity systems (a) a high, ipm lotoi (shown below its normal position within stator) produces turbulence and cavitation as blades pass each other (b) a rotating disk creates a deep vortex to rapidly refresh the surface, and up- and downtumed teeth at the edge cause impact, turbulence, and sometimes cavitation and (c) the clearance of a high rpm rotor can be reduced as the batch...

Higher annular velocity-low viscosity system or low annular velocity-higher viscosity systems can be selected. Annular velocity can be substituted for viscosity in lifting particle. Annular velocity at 150 ft/min should be sufficient for borehole cleaning with 1 cp viscosity clear salt water. 

Like the high-build epoxy paints, these are solvent-free low-viscosity systems which are readily applied onto a prepared level substrate to provide a jointless thin (thickness approximately 1.5 mm) chemically resistant flooring in a single application. ... 

These types of agitator are used in low-viscosity systems (ji < 50 kg m 1 s-1) with high rotational speed. The typical tip speed velocity for turbine and intermig is in the region of 3 m s 1 a propeller rotates faster. These impellers are classified as remote clearance type, having diameters in the range 25-67% of the tank diameter. 

Sufficient information is available on low viscosity systems for the estimation of the power requirements for a given duty under most conditions of practical interest. 

Illustration Satellite formation in capillary breakup. The distribution of drops produced upon disintegration of a thread at rest is a unique function of the viscosity ratio. Tjahjadi et al. (1992) showed through inspection of experiments and numerical simulations that up to 19 satellite drops between the two larger mother drops could be formed. The number of satellite drops decreased as the viscosity ratio was increased. In low-viscosity systems p < 0(0.1)] the breakup mechanism is self-repeating Every pinch-off results in the formation of a rounded surface and a conical one the conical surface then becomes bulbous and a neck forms near the end, which again pinches off and the process repeats (Fig. 21). There is excellent agreement between numerical simulations and the experimental results (Fig. 21). 

Bubble Column 1. No moving parts 2. Simple 3. Low equipment costs 4. High cell concentration 1. Poor mixing 2. Excessive foaming. 3. Limited to low viscosity system... 

Figure 29 shows the importance of orientation on sideentering mixers on low-viscosity systems. The mixer must be inclined about 7° from the tank diameter, to ensure a... 

Schmidt (102) observed that flooding and minimum wetting are caused by two different mechanisms. A low-liquid-rate column may therefore flood even when it operates below the MWR. This is most likely to occur in vacuum systems (where liquid rates are low and vapor velocities are high) and in high-surface-tension, low-viscosity systems. 

Epoxy acrylate oligomers that are used in uv/EB curing are very low-viscosity systems with high vapor pressures. Within this group of oligomers, there are several major subclassifications aromatic difunctional epoxy acrylates, acrylated oil epoxy acrylate, novolac epoxy acrylate, aliphatic epoxy acrylate, and miscellaneous epoxy acrylates. Characteristics of these various classes are summarized in Table 4.8. 

High-Viscosity Systems All axial-flow impellers become radial flow as Reynolds numbers approach the viscous region. Blending in the transition and low-viscosity system is largely a measure of fluid motion throughout the tank. For close-clearance impellers, the anchor and helical impellers provide blending by having an effective action at the tank wall, which is particularly suitable for pseudoplastic fluids. 

If the liquid flow is reversed on successive trays, the cross-flow enhancement of efficiency is greatly reduced, but still present. Thus, tray efficiencies of 110% or more are sometimes observed for low-viscosity systems, such as depropanizers or butane-isobutane splitters. 

Calculate the number of theoretical plates that can be achieved with a pressure of 10 bar and 10 pin silica under optimum conditions (low viscosity system). 

There are notable exceptions, however, such as the CEP Lodge Stressmeter . This rheometer is unique in that it measures both viscosity and first normal stress difference, Nl. Both laboratory and in-line configurations are available. The instrument is shown in Figure 4.13. The Lodge Stressmeter is applicable to low-viscosity systems and available commercially from Chemical ElectroPhysics Corp. (Delaware, NJ). 

High cell concentration Limited to low viscosity system... 

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