Application of three-dimensional phase-doppler anemometry to mechanically agitated crystallizers

A three-dimensional phase-Doppler anemometer is applied to suspensions agitated by a pitched-blade turbine in a cylindrical, flat-bottomed, baffled tank. The complete local, instantaneous, three-dimensional velocity vector of the fluid and of suspended process particles, are determined simultaneously. Measurements have been carried out at a limited number of locations, in order to examine the spatial variation of flow and turbulence characteristics, and of process particle behaviour and concentration. It is found that the turbulence in the bulk of the tank is not entirely isotropic. The difference in magnitude and direction of the mean velocity of the fluid and of the process particles, is usually small. Differences in the root-mean-square value of the fluctuating velocities of the two phases can only be observed in the discharge flow of the impeller. The resultant, three-dimensional, turbulence length macroscale varies almost by a factor of two, the energy dissipation rate by a factor of 18 and the process particle concentration by a factor of three. Low frequency, decaying oscillations in the autocorrelation coefficient have been recorded out in the bulk of the tank.