Aerated and unaerated power consumption and flow patterns in a 0.56 m diameter agitated vessel containing water with dual Rushton turbines have been studied. Under unaerated conditions with a liquid height-to-diameter ratio of 2, an impeller spacing of 2 to 3 times the impeller is required for each to draw an amount of power equal to a single impeller. For aerated conditions, if a similar spacing is used, equations for the flooding-loading transition and for power consumption for a single Rushton impeller can be extended relatively easily to dual systems. All results for this spacing are explained by reference to bulk flow patterns and gassed-filled cavity structures and the proportion of sparged gas flowing through the upper impeller is also estimated. Such a spacing is generally recommended since it maximizes the power draw and hence the potential for oxygen mass transfer. Data are presented for other spacings but the results do not fit in easily with single agitator studies because strong impeller-impeller flow pattern interactions occur.

No abstract

No abstract

No abstract

Power for agitation has been measured under aerated and unaerated conditions in a 0.29 m vessel of Rushton dimensions at specific powers up to 18 W/kg. The lluids studied were water. Newtonian solutions up to 19 m Pas and non-Newtonian shear thinning fluids some of which also exhibited a yield stress and some of which were viscoelastic. For the unaerated case. the power number-Reynolds number plot is in good agreement with the literature. For the aerated case, the resull can conveniently be divided into three Reynolds number regions. At Re > -900. the data obtained for the solutions is not markedly different [0 that for water except that a higher impeller speed is required to achieve complete gas dispersion. For -10 < Re < -900. the power drawn is independent of gassing rate and greater levels of elasticity and the presence of a yield stress leads to the lowest power numbers. For Re < --10. the gassed and ungassed power numbers are equal.