Suction, power and efficiency characteristics

There are stirring operations in chemical engineering in which a large gas throughput is involved (e.g, blowing out of volatile compounds from a liquid), for which a minimization of stirrer power input is desirable. The condition for which P/q = min can be obtained from the process characteristics Q = /j(Fr) and Ne = f2(Fr) (Fig. 4.31 and 4.32), if the Ne, Q, Fr numbers are combined in a way, that a dimensionless expression for P/q arises  

as the components themselves, is a fimction of the Froude number. Fig. 4.33 shows the course of this function. It shows, that there are two operating ranges  

For Fr 10, F eFrlQ = const applies, i.e. P/q oc d. In this range P/q increases directly proportionally with scale P/q cc d. (In case of a scale-up of n = 1 10, the full-scale device required a ten-fold stirring power for the same gas throughput ) 

For Fr 10, hollow stirrer operate still less economically, since here F cFr/Q increases approximately proportionally with Fr ex. n d P/q ex d  

The fact, that hollow stirrers are not suitable on an industrial scale for sucking up large gas throughputs, could be described small is beautiful . Here, the gas throughput and the stirrer power must be decoupled from one another, by feeding a fast rotating stirrer from underneath by externally compressed gas. 

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