Impeller-Type Mixing Equipment

Dickey, D. S., et al. 200 ). Mixing Equipment (Impeller Type) AIChE Equipment Testing Procedure, 3rd ed., AIChE, New York. 

The commonly used types of mixing equipment can be placed in the broad categories (1) mechanical agitators, (2) inline motionless mixers, (3) tank jet mixers, and (4) miscellaneous. The nature and type of agitator used depends upon the scale and type of mixing and upon the fluids being mixed. The broad classes of impellers are ... 

Figure 5-5X. Type R-500. Very high shear radial flow impeller for particle size reduction and uniform dispersion in liquids. By permission, Lightnin, (Formerly Mixing Equipment Co.) a unit of General Signal.

A.i.Ch.E. Standard Nomenclature for Mixing from A.i.Ch.E. Standard Testing Procedure for Mixing Equipment (Impeller Type), American Institute of Chemical Engineers. 

Traditional scale-up rules Table 4.2 (These scale-up rules have been used for many types of equipment scale-ups, e.g., the stirred vessel for mixing of the fluids that have no reaction ability. It is clarified that the distribution of the dimensionless turbulent statistical values by making use of impeller tip velocity UT(= ND) becomes identical regardless of impeller rotational... 

An extensive compilation was published by Rushton et al. (R13), giving the results of a program of measurements carried out by the Mixing Equipment Company. The data cover a wide range of impeller types, impeller and tank sizes, liquid properties, and operating conditions. They also presented their results in the form of a function of dimensionless groups ... 

Mixing equipment, impeller type, prepared by the Equipment Testing Procedures Committee of the American Institute of Chemical Engineers, New York, 2001. 

In practice, it is often not possible to calculate the selectivity for this type of process from first principles. Experimental studies have to be done under various conditions, leading to an empiricd optimum on a small scale. It has been shown in section 5.2.2 that the selectivity can be sensitive to the meso-mixe(hiess, and that these can both decrease on larger scales. It may be practical to study the reaction first in a well mixed semi-batch reactor, preferably equipped with an effective turbine impeller, or propeller. The feed tube should end in the exit flow of the impeller. With this equipment one measures the influence of the feed rate on the selectivity. It may be that a sufficiently high selectivity is obtained when the feeding time has a certain minimum value. The specific energy dissipation should be measured or calculated. 

A qualified mixing equipment supplier can assist with process sizing, equipment selection, impeller options, capital versus operating cost evaluation, testing, reliability, and service. In this chapter we describe each type of support and its importance in the equipment selection process. Criteria for choosing a qualified supplier are identified. 

Equipment suitable for reactions between hquids is represented in Fig. 23-37. Almost invariably, one of the phases is aqueous with reactants distributed between phases for instance, NaOH in water at the start and an ester in the organic phase. Such reac tions can be carried out in any kind of equipment that is suitable for physical extraction, including mixer-settlers and towers of various kinds-, empty or packed, still or agitated, either phase dispersed, provided that adequate heat transfer can be incorporated. Mechanically agitated tanks are favored because the interfacial area can be made large, as much as 100 times that of spray towers, for instance. Power requirements for L/L mixing are normally about 5 hp/1,000 gal and tip speeds of turbine-type impellers are 4.6 to 6.1 i7i/s (15 to 20 ft/s). 

In the research laboratory it is important to recognize the effect of mixing on reaction rate or on other performance criteria. Energy must he supplied to produce fluid motion, thus, to compare mixing with different equipment or with different sizes of the same type impeller, it is essentia] that the comparisons be made on the basis of equal power input. 

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