The confined impeller stirred tank (CIST): A bench scale testing device for specification of local mixing conditions required in large scale vessels

A new stirred tank geometry, the confined impeller stirred tank (CIST), was designed to provide repeatable testing of the effect of mixing on the performance of chemical additives at the bench scale. The CIST (T = 0.076 m, H = 3T) is filled with five or six impellers. Three impeller geometries were tested: A310, Rushton and Intermig. This paper presents the following hydrodynamic characteristics of the CIST: power number, flow number, momentum number, velocity profiles at different locations in the tank and the transition point from fully turbulent to transitional flow. Based on the scaled velocity profiles, the CIST was able to keep the flow turbulent at Re < 2000 for Rushton turbines and 3200 for Intermigs. The ratio ɛmax/ɛaverage was lower for the CIST than for a conventional stirred tank, indicating that the energy dissipation is more uniformly distributed in the CIST. The CIST consistently maintains turbulent flow down to a Reynolds number 10× smaller than that needed in a conventional stirred tank.