APPLICATION OF 3-DIMENSIONAL PHASE-DOPPLER ANEMOMETRY TO MECHANICALLYAGITATED 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 vel ocity vector of the fluid and of suspended process particles, are dete rmined simultaneously. Measurements have been carried out at a limited number of locations, in order to examine the spatial variation of flo w and turbulence characteristics, and of process particle behaviour an d concentration. It is found that the turbulence in the bulk of the ta nk is not entirely isotropic. The difference in magnitude and directio n of the mean velocity of the fluid and of the process particles. is u sually small. Differences in the root-mean-square value of the fluctua ting velocities of the two phases can only be observed in the discharg e flow of the impeller. The resultant, three-dimensional, turbulence l ength macroscale varies almost by a factor of two, the energy dissipat ion rate by a factor of 18 and the process particle concentration by a factor of three. Low frequency, decaying oscillations in the autocorr elation coefficient have been recorded out in the bulk of the tank.