6.1 Flow Patterns in Agitated Vessels

  • In the usual case of a vertical shaft, the radial and tangential velocity components are in a horizontal plane, and the longitudinal components is vertical. The radial and longitudinal components are useful and provide the flow necessary for the mixing action. When the shaft is vertical and centrally located in the tank, the tangential component is generally dangerous.

  • The tangential flow follows a circular path around the shaft, creates a vortex at the surface of the liquid. If solid particles are present, circulatory currents tend to throw the particles to the outside by centrifugal force, from where they move downward and to the centre of the tank at the bottom. Instead of mixing, its reverse—settling occurs.

  • In an unbaffled vessel circulatory flow is induced by all types of impellers, whether axial flow or radial flow.