The present study was carried out by experimenting in a stirred tank of unbaffled system employed with concave blade impeller. In this study the influence of impeller diameter (d), tank diameter (D) and impeller clearance depth (C) on vortex depth is investigated at various impeller rotational speeds. The higher vortex depth is observed when the impeller is closer to the tank bottom. Relative vortex depth increases with the increase in the impeller diameter in all cases of impeller clearance depth at constant D. Smaller tank diameter gives higher relative vortex depth, when d is constant at different impeller clearance depths. Critical speed is found decreasing with the increase in C/D and d/D ratio. Finally, a scale up criteria for relative vortex depth has been developed, which is valid for geometrically similar conditions.
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