Mixing duty

The stirring requirements for average mixing duty are estimated at 5 hp per 100 ft , and combining this with the cost data on mixer-motor installations gives... 

Typical values for the impeller clearance off the vessel bottom are 7/4 for hydrofoil impellers and 7/3 for pitched-blade turbines. Hydrofoil impellers may be a poor choice when solid suspension is accompanied by other mixing duties, such as liquid-liquid dispersion or gas dispersion. For such cases, a multiple impeller system consisting of a high-efficiency impeller in combination with a 45"" pitched-blade impeller should be evaluated. Small pitched blade impellers with a... 

The wide range of mixing equipment available commercially reflects the enormous variety of mixing duties required in the chemical, paint, food, and pharmaceutical industries. Some of these duties are listed below ... 

Mixing duties in the plastics industry are often carried out in either single- or twin-screw extruders. The feed to such units will usually contain the base... 

The mixing problems considered so far have related to batch systems in which two or more materials are mixed together and uniformity is maintained by continued operation of the agitator. Consideration will now be given to some of the equipment used for continuous mixing duties. 

With regard to the physics, BHR believe that a large scale adiabatic reactor could be used with high mass transfer and near plug flow. Temperature is around 100°C and the residence time can be seconds to a few minutes. The reactor pressure should be sufficient to suppress methanol boiling at the desired temperature. Challenges are associated with the mixing duty and the fact that operation is currently mainly batch mode. 

Six rectangular blades are mounted symmetrically around the circumference of a horizontal carrier disk and perpendicular to it, as shown in Figure 13.2. The flat blade disk turbine is used especially on gassing duties because of its good dispersing effect Under certain conditions, it can also be used for other mixing duties. 

Ram shape and clearance modification can help to enhance the performance of a mixer, particularly on machines dedicated to a restricted mixing duty. This should be discussed with the mixer manufacturer to get the best from the equipment. 

CMC. CMC (sodium carboxymethylcellulose) solutions need to be made up from the appropriate grade of powdered CMC. Although specialist equipment can be obtained to perform this mixing duty, a laboratory mixing vessel can also be used for this process. Care must be taken to feed the powder slowly. 

Expressing the correlation in this way makes it very useful for design since the properties of the jet are separated from the properties of the mixing duty (the blend time, vessel size, and liquid physical properties). 

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