Power Consumption of Gassed Liquids

Power Consumption of Gassed Liquids 297 Superficial Liquid Velocity 297 Design Procedures 297... 

Figure 10.11. Power consumption, (a) Ratio of power consumptions of aerated and unaerated liquids. Q is the volumetric rate of the gas (O) glycol ( X ) ethanol ( ) water. [After Calderbank, Trans. Inst. Chem. Eng. 36, 443 (1958)]. (b) Ratio of power consumptions of aerated and unaerated liquids at low values otQ/Nd3. Six-bladed disk turbine ( ) water ( ) methanol (10%) (A) ethylene glycol (8%) (A) glycerol (40%) Pg = gassed power input P = ungassed power input Q = gas flow rate IV = agitator speed d = agitator-impeller diameter. [Luong and Volesky, AIChE J. 25, 893 (1979)].

When gas is bubbled below the impeller, the power drawn by the agitator decreases relative to the non-gassed liquid. This is because the gas/liquid mixture creates a zone of lower density below the stirrer, that strongly reduces the power consumption. From the point of view of design, however, it should be noted that the drive-motor- should be designed for the most demanding case, that is, the ungassed condition. 

As already discussed in context with the single-phase simulations, boundary conditions at the impeller are predicted from measured data of the averaged velocities. The gassed linear liquid velocities differ from the ungassed velocities because impeller power consumption and pumping capacity of the impeller decrease due to gassing. 

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