화학공학소재연구정보센터
Chemical Engineering Science, Vol.57, No.18, 3939-3952, 2002
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
The flow patterns established in a continuously-fed stirred tank, equipped with a Mixel TT axial-flow impeller, have been investigated by laser Doppler velocimetry, for a high and a low value of mean residence time-mixing time ratio. The pseudo-two-dimensional axial-radial-velocity vector plots, as well as the spatial distributions of the tangential velocity component and the velocity profiles around the impeller, show that the interaction between the incoming liquid and the liquid entrained by the agitator rotation cause the flow pattern in the vessel to become strongly three-dimensional, especially in the region between the plane, where the feeding tube lies, and the 180degrees-downstream plane. The increase in the liquid flow rate and the location of the feed entry both affect the flow pattern, with the latter having a more pronounced effect. The overall process, in this mode of operation, depends upon the appropriate configuration and choice of parameters: for conditions corresponding to high liquid flow rates, the flow patterns indicate the possibility of short-circuiting, when the liquid is fed into the stream being drawn by the agitator and when the outlet is located at the bottom of the vessel.