Minimum rotor tip speed

The foam centrifuge compresses the primary foam (db 1 mm) to a flowable secondary foam (db 0.05-0.1 mm). Preliminary experiments showed that a foam density of ca. 0.5 kg/1 is necessary [533], which was attained with a rotor tip speed of ca. 20 m/s. A similar trend of the density of the compacted foam pf as a function of the rotor tip speed u was achieved with the foam turbine [171] for which a foam density of 0.35 kg/1 was sufficient for the secondary foam to flow. Fig. 4.26 shows these measurements for both types of foam breaker and different foams and also shows the large effect the concentration of the foaming agents exerts in the range 0.2-2.0 mmol/1 = 0.073-0.73 g/L (CMC is the Critical Micelle Concentration). However, Fig, 4.26 also shows that to realize the same flowability of the foam 

For three tensides (Triton X, Mersolat H and CTAB), whose concentrations in the liquid were c = 1 CMC, the following relationship was determined between the average bubble diameter di2 in foam and the liquid fraction in foam (= foam density pf) with the foam turbine [171]  

From this it follows that a compressed secondary foam with 0.50 (a foam density pf 0.5 kg/1) consisted of bubbles with 1/32 0.1 mm, whereas the primary foam with rp 0.10 (= foam density pf 0.1 kg/1) contained bubbles of 32 w 2 mm. Increasing the liquid viscosity from 1.0 to 6.6 mPa s had no effect on this result. 

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