Relative power demand, gassed

A common way to determine the agitator power under gassed conditions is to use the k-factor, sometimes called the relative power demand, defined as the ratio of gassed to ungassed shaft power ... 

In Eq. (6) Kq/u (=Pg/Pxj) is the gassing factor or relative power demand (RPD) between (otherwise identical) gassed and ungassed systems, g/u depends on the impeller type, Qq, N, and D, and generally decreases with increasing gas flow number, Flo- A summary of typical g/u values for popular impellers at high gas flow rates (Mg = 0.1) is given in Table 3. 

Fig. 6 Relative power demand for a gassed Rushton turbine D/T = 0.4). (Data from Refs.ti " ].)...

Figure 11-7 (a) and (b) ventilated gas cavity forms [ a) vortex cavities (b) large cavity] on turbine blades and (c) relative power demand for a gassed Rushton turbine (D/T = 0.4). (Data from Warmoeskerken et al, 1982.)... 

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. 

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