Agitators, design

The mass-transfer coefficients depend on complex functions of diffii-sivity, viscosity, density, interfacial tension, and turbulence. Similarly, the mass-transfer area of the droplets depends on complex functions of viscosity, interfacial tension, density difference, extractor geometry, agitation intensity, agitator design, flow rates, and interfacial rag deposits. Only limited success has been achieved in correlating extractor performance with these basic principles. The lumped parameter deals directly with the ultimate design criterion, which is the height of an extraction tower. 

Mixers and agitators designed for flammable liquids or dusts should be constructed to minimize fire and explosive possibilities. Electrical equipment should follow the requirements of Uie National Electrical Code. Equipment should be bonded and grounded to prevent Uie accumulation of staUc electricity. 

Careful consideration has to be given to agitator design within a bioreactor because it controls the operation of the bioreactor. 

In discussing equations 9.207 and 9.208 Fletcher 96 has summarised correlations obtained for a wide range of impeller and agitator designs in terms of the constant before the Reynolds number and the index on the Reynolds number as shown in Table 9.11. 

According to Wisseroth, the agitator design was quite important, and was very similar to those shown in reference 1. The speed was adjustable from 0-360 rpm and a gland packing seal was used. For special operations, metallic balls were added to the reactor to improve temperature stability (10). 

Although experts in agitator design are loath to admit to using such a simplistic rule, most scaleups of conventionally agitated vessels are done at or near constant power per unit volume. The consequences of scaling in this fashion are explored in Example 4.7... 

Perform each step in a separate vessel with the design optimized for that operation this includes vessel size, pressure rating, emergency relief system design, materials of construction, utilities, and agitation design. 

When mass transfer coefficients are not determinable, agitator design may be based on superficial liquid velocities with the criteria of Table 10.2. 

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