The effect of impeller/tank, configurations on fluid-particle mass transfer

Abstract Integral mass transfer coefficients for dissolving monodisperse spherical sodium chloride crystals have been measured for six-blade disc turbines, two-blade flat paddles and four-blade 45°-pitch turbines in closed vessels 0.14 and 0.28 m in diameter and of Rushton dimensions. Thirtynine different geometries were employed and in all cases the coefficient obtained at the stirrer speed at which the crystals were just fully suspended was approximately constant. The power per unit mass required to achieve this coefficient was some 30 times less in some geometries than in others. The specific power consumed in just suspending the particles was always less in the larger for geometrically similar impeller/ tank configurations. In general, the larger impellers with a small clearance above the vessel base, consumed less power than other configurations, but the 45°-pitch turbine consumed least and did not follow this rule. Photographs of particle suspension and flow patterns allowed an explanation of this apparent anomaly.