Study by laser Doppler anemometry of the turbulent flow induced by a Rushton turbine in a stirred tank: Influence of the size of the units—I. Mean flow and turbulence

Abstract The hydrodynamical characteristics of the flow induced by a six flat blades disk turbine were determined by laser Doppler anemometry. Two different cylindrical tanks, geometrically similar, with a flat bottom and four vertical baffles were used, giving liquid (water) volumes of 70 and 200 l, for a height of liquid equal to the tank diameter. The turbines were located at the midheight of the water level in the tank. Mean velocities and velocity fluctuations were measured, at different impeller rotational speeds, in two vertical planes: the median plane between two baffles and the plane of a baffle. When divided by the blade tip velocity, the non-dimensional profiles were observed to be independent of the impeller rotational speed. Therefore the following dimensionless groups, the discharge flow number and the circulation flow number, were calculated. A comparison of the results obtained with the two different vessels gives information on the influence of the size of the vessel. Some scale-up rules for agitation can then be suggested.