Agitator power tank

In these equations, a is the specific interfacial area for a significant degree of surface aeration (m2/m3), I is the agitator power per unit volume of vessel (W/m3), pL is the liquid density, o is the surface tension (N/m), us is the superficial gas velocity (m/s), u0 is the terminal bubble-rise velocity (m/s), N is the impeller speed (Hz), d, is the impeller diameter (m), dt is the tank diameter (m), pi is the liquid viscosity (Ns/m2) and d0 is the Sauter mean bubble diameter defined in Chapter 1, Section 1.2.4. 

In stirred tanks, the power input to agitate the tank will depend on the physical properties of the liquid. In tubular reactors, the axial dispersion in empty tubes may be estimated [e.g., Wen in Petho and Noble (eds.), Residence Time Distribution Theory in Chemical Engineering, Verlag Chemie, 1982] as... 

Values for the constant K and the indices b and c for various types of agitator, tank-agitator geometries, and dimensions can be found in the literature see Rushton et al. (1999). A useful review of the published correlations for agitator power consumption... 

In the case of stirred tank fermenters, heat that must be dissipated includes not only that generated by microbial metabolic activity but also that evolved from agitation power (i.e., 2500Btu/shp-hr) and expansion of sparged gas. This can lead to scale-up problems because vessel volume is proportional to vessel diameter cubed, while heat transfer area is proportional only to vessel diameter squared. 

For high aeration values, gas expansion power Pgas can reach the magnitude of the aerated agitator power Pg. If gas expansion power is greater than or equal to the stirrer power, there is the likelihood of impeller flooding, which limits gas dispersion to the central region of the tank. 

The most important choices in the design of batch reactors are reactor volume selection of the agitator speed of the agitator power consumption geometry of the tank, including baffles and heat exchange area (internal and external). 

Agitator power requirements for ungassed systems Agitator requirements for gas-liquid dispersions Temperature tank diameter Volume of reactor contents Superficial gas velocity... 

Fig. 4.2-6 Temperature evolution in a continuously operated tank with input of agitator power (77 = normalized dimensioidess agitator power)...

If the correlations are well established to determine the agitation power in absence of a gas phase, Pq> for different stirrers (71), the situation is more complex for the case of aerated tanks. Most authors propose to represent the decrease of the agitation power in presence of a gas phase at the same stirring velocity, by ccjrrelations between Pg/P aerated number... 

Impeller Diameter/Tank Agitation Power Flow Reynolds... 

A baffled fermentation tank for a pilot plant is to be l.S m in diameter and will contain liquid to a depth 2.0 m. The flat-blade disk turbine impeller, 0.5 m diameter, will be located m from the bottom of the vessel. Air at a superficial velocity of 0.06 m/s will be introduced beneath the impeller. The temperature will be 27 C, and the liquid properties may be taken as those of water. Small-scale tests indicate that a suitable agitator power will be 0.5 kW/m of liquid. At what speed should the impeller be turned ... 

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