Water flow in a stirring mixer driven by a six-blade Rushton turbine has been quantified by a Particle Image Velocimetry(PIV) for a blade rotational speed of 100 r.p.m. Three different fields of view, top, middle and bottom covering the whole r-z plane were used to measure the bulk velocity field in the entire tank. A non-intrusive Planar Laser-Induced Fluorescence(PLIF) technique was applied to study the turbulent mixing process in a Rushton turbine reactor. Instantaneous and ensemble averaged concentration fields are obtained by measuring the fluorescence intensity of Rhodamine B tracer excited by a thin Nd:Yag laser sheet illuminating the whole center plane of the stirred tank. The gray level images captured by a 14-bit cooled CCD camera can be transformed to the local concentration values using a calibration matrix. Three different dye injection points were selected to observe the mixing characteristics in upper and lower bulk flow regions and the impeller flow region. It is found that the general features of the mixing pattern seem to be quite dependent on the local flow characteristics. There exist distinct two time scales: the rapid decay of mean concentration in each region after the dye infusion reflects the large scale mixing while the followed slow decay reveals the small scale mixing.
ASJC Scopus subject areas
- Aerospace Engineering