Investigation by laser doppler velocimetry of the effects of liquid flow rates and feed positions on the flow patterns induced in a stirred tank by an axial-flow impeller

Abstract

The (ow patterns established in a continuously-fed stirred tank, equipped with a Mixel TT axial-(ow impeller, have been investigated bylaser Doppler velocimetry, for a high and a low value of mean residence time—mixing time ratio. The pseudo-two-dimensional axial– radial-velocityvector plots, as well as the spatial distributions of the tangential velocitycomponent and the velocitypro;les around the impeller, show that the interaction between the incoming liquid and the liquid entrained bythe agitator rotation cause the (ow pattern in the vessel to become stronglythree-dimensional, especiallyin the region between the plane, where the feeding tube lies, and the 180◦-downstream plane. The increase in the liquid (ow rate and the location of the feed entryboth a$ect the (ow pattern, with the latter having a more pronounced e$ect. The overall process, in this mode of operation, depends upon the appropriate con;guration and choice of parameters: for conditions corresponding to high liquid (ow rates, the (ow patterns indicate the possibilityof short-circuiting, when the liquid is fed into the stream being drawn bythe agitator and when the outlet is located at the bottom of the vessel.