A Study of Ventilated Gas Cavities on DiscTurbine

Authors: S A Manning G J Jameson

Publish Date: 1992

Volume: , Issue: , Pages: 225-231

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Abstract

The presence of ventilated gas cavities on the rear of impeller blades is an important characteristic of gasliquid stirred systems Cavities blanket the rear of the blades reducing the impeller power consumption the interfacial area and the rate of interphase mass transfer Few fundamental studies involving measurements in and around cavities appear in the literatureIn this study air was supplied through a hollow shaft to one blade of a twoblade standard discturbine impeller The size of ventilated cavities produced at various impeller speed/gas flowrate combinations was measured A specially designed bearing mounted on the impeller shaft allowed accurate measurements of the gas pressure inside the cavities to be madeFor constant gas flowrates the impeller speed was increased from zero At very low impeller speeds no cavities were formed At higher speeds cavities formed which grew in length as the speed increased The cavities grew to a maximum size which increased with gas flowrrate Once the maximum size was reached further increases in the impeller speed caused the tails of the cavities to be eroded resulting in shorter cavities Cavity pressure was almost constant during the cavity growth region dropping only slightly At higher impeller speeds substantial reductions in cavity pressure were observed which mirrored the reduction in cavity size The critical speed for the transition between cavity growth and dispersion regions was found to increase with increasing gas flowrateModels are presented that relate the growth region Zone 1 and dispersion region Zone 2 of cavity size with the cavity internal pressure for various impeller operating conditons The implications of these results to the power consumption and gas dispersion quality in impeller stirred gasliquid reactors are discussed

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