Abstract
The effects of operational parameters such as vessel size, impeller design, diameter and blade number, Reynolds number ( Re) and baffle number on the flows and specifically the macro-instability (MI) phenomena in stirred vessels were studied. Laser anemometry and particle image velocimetry techniques were employed to measure the mean flow and turbulence structures in vessels of diameters in the range 100–400 mm. The data show that the characteristic frequency of the MIs, f′ = f/ N, although constant for high Res, it exhibits higher value(s) over an appreciable region in the vessel for Re < 17,500. The presence of the MI is shown to broaden the measured r.m.s. levels in the vessel by up to 23%. Measurements of the tangential mean velocities near the vessel surface did not reveal any clear evidence of scaling of the flow with impeller diameter, blade number, or the number of baffles. The implications of the results for an improved understanding and a more accurate and quantitative characterisation of the flows in stirred tanks are discussed and assessed.
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