Flow parameters were measured in a baffled, turbulent, stirred tank agitated by a six-blade, disk style turbine. The working fluid was air. Mean and fluctuating velocities were measured between the blades of the impeller with a probe mounted on the spinning impeller. Mean velocities, turbulent velocities, one-dimensional energy spectra, and Eulerian autocorrelation functions were measured in the impeller stream by using the shielded hot-wire anemometer of Gunkel et al. (1971) which permits the measurement of turbulence parameters in flows of very high turbulence intensity. Reliable impeller pumping capacities were obtained yielding Q r a d / N D 3 = 1.0 at the impeller periphery. An energy balance on a control volume containing the impeller and the impeller stream showed that the energy put into the tank via the impeller appeared as a net efflux of kinetic energy leaving the control volume. Therefore, most of the energy input to the tank is dissipated in the bulk of the tank.
SCOPENo progress in the understanding of mixing operations in stirred tanks can be achieved without a better picture of the flow phenomena in stirred tanks. The main objectives of this study were: to measure flow parameters in a turbulent stirred tank, from them to determine how the energy put into the tank was dissipated, and then to derive theoretically supported scale-up procedures for operations in stirred tanks. The achievement of this last objective is of most immediate importance for practical applications.Previous studies on the flow phenomena in the impeller stream of a stirred tank have reported mean velocities, turbulent velocities, one-dimensional energy spectra, and correlation functions (Kim and Manning, 1964;Bowers, 1965;Cutter, 1966; Sat0 et al., 1967;Mujumdar et al., 1970;Rao and Brodkey, 1972;Cho et al., 1971). The main shortcoming of these studies is the poor precision of the experimental techniques which were not suitable for the high turbulence intensities (up to Svo)found in stirred tanks. Nevertheless, Cutter (1966) concluded that 70% of the energy put into the tank was dissipated within the impeller and the impeller stream, and only 30y0 was dissipated in the bulk of the tank. In the first part of the present paper, accurate flow parameters are reported in the impeller stream from a six-blade, dipk style turbine. An energy balance is then used to determine the amount of energy dissipated in the impeller and the impeller stream.
CONCLUSIONS A N D SIGNIFICANCEA very complete picture of the flow pattern in the neighborhood of a six-blade, disk style turbine impeller has been obtained. For the first time velocities between the blades of a rotating impeller have been measured. These measurements indicated that four vortices are present between each pair of blades, two above and two below the disk.Mean velocity profiles in the impeller stream showed a jet like behavior, with the impeller stream entraining fluid as it traveled from the periphery of the impeller to the tank wall. Integration of the velocity profiles yielded ...