Vortex aeration

Voluntary materials standards, 15 742 Voluntary sulfur, 23 569 von Liebig, Justus, 25 628 von Neumann law, 12 15 von Willebrand factor, 4 85-86,12 137,147 Vorsyl separator, 16 634 Vortex aeration, 15 694 Vortex finder, in hydrocyclones, 22 285, 286... 

Chain et al. also report some results from operation without baffles or a sparger under conditions where a vortex was produced, enough air was drawn in through the vortex to give oxygen uptake rates equal to those observed with baffled operation and a submerged air inlet. However, Kneule (K6), in a very brief report, finds that aeration under the usual baffled conditions is preferable to vortex aeration. 

Use only stainless steel tanks minimize vortex formation to prevent aeration. Product attacks glass avoid contact with glass. 

In recent years attempts have been made to improve the gas-liquid mass transfer by changing the design of the mechanically agitated vessel. Mann et al. (1989) evaluated the use of horizontal baffles mounted near the gas-liquid surface. Horizontal baffles prevent vortex formation, generate less shear than standard baffles, increase gas holdup, and improve gas-liquid mass transfer. The latter two results are due to the rotational flow below the baffles, which causes gas bubbles to move upward in a spiral trajectory and induces surface aeration. For a 12-inch i.d. and 18-inch-tall stirred vessel, they showed kLat to be improved by a factor of 1.6 to 2.3 with 30 to 50% lower agitation power compared to the standard vessel. 

Consequently, for the case of surface-aerated bioreactors, the most important condition to avoid is the formation of a vortex that can lead to the entrainment... 

Fig. 1.22 Gas entrainment via vortex in comparison to the volume aeration by self-aspirating hollow stirrers (type "three-edged stirrer ) from [609]. 

Equipment for blending resins with catalyst and accelerator should ensure that such blending is uniform. However, over vigorous blending which results in air becoming dispersed in the resin mix should be avoided. In particular very high speed propeller mixers which create a vortex and aerate the resin should not be used. 

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