Delta paddle mixing impeller--some hydrodynamic studies

Local measurements of the pressure difference across a 20 cm diameter delta impeller blade, and the pressure on the blade, have been carried out using a rotating manometer mounted on the shaft. The impeller was driven at speeds between 1.33 and 3.67 r.p.s. in a 30 cm square tank containing 27 l of water. The velocity field has been observed using cotton streamers taped to the blade, and by photographing dispersions of particles. Flow enters the top of the triangular blade and is then deflected outwards across the rear of the blade, with vortex shedding near the outer tip. The pressure profiles show a sharp minimum at a radius of 6 cm at the rear of the blade and this corresponds to maximum velocity. The flow pattern and mixing performance are compared with those of a conventional Rushton turbine. The good liquid-liquid dispersion characteristics of the delta paddle impeller (observed previously) are attributed to a ligament stretching mechanism of drop breakup.