The rates of oxygen mass transfer into a simulated fermentation medium, made up of 16 kg of paper pulp per m3of aqueous sodium sulphite solution with a cupric ion catalyst, were determined in vessels of 0·187, 0·291 and 0·451 m dia., using flat-bladed turbine impellers, and the effect of varying impeller dimensions and operating speed were investigated. Above a critical impeller tip speed the volumetric mass transfer coefficients obtained at the same speed with different power inputs (produced by variations in the impeller blade dimensions) could be represented by the sum of two terms, one depending on the impeller speed, the diameters of the impeller and vessel, and the height of pulp suspension in the vessel, and the other function of the power input per unit volume and the air velocity through the vessel. At each impeller speed the increase in the volumetric mass transfer coefficient with power input was found to be greater below a certain power input per unit volume, and a correlation for this power per unit volume was based on it corresponding to a change in the rate of air recirculation through the impeller. The expression for the mass transfer coefficient provides a more accurate basis for scale-up than the use of simple rules, such as constant power per unit volume. © 1973.
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