Stirred tanks are ubiquitous in the chemical, polymer, and pharmaceutical industries and used extensively for conducting a variety of single liquid phase and multiphase operations. Turbulent flow is most often encountered in stirred tanks. While efficient mixing is often achieved under turbulent conditions, there are many applications in which turbulence is precluded because fluids are too viscous or shear sensitive materials may be damaged by vigorous agitation. In such cases, stirred tanks must be operated under laminar flow conditions. The low Reynolds number regime arises in many practical applications, such as culture of shear-sensitive cells, manufacture of creams and detergent. Therefore it is necessary and important to study the laminar flow in stirred tanks.
Both single phase and solid-liquid two-phase systems are frequently encountered in stirred tanks, and the presence of solid particles makes the flow in stirred tanks more complicated. Little literature on laminar solid-liquid flow in stirred tanks is available. To the authors’ best knowledge, only Jones and Weinberger (1) studied the laminar solid-liquid flow in a baffled tank stirred by a Rushton turbine. Dyster et al. (2) experimented on the radial discharge laminar flow in a baffled stirred tank. Bakker et al. (3) using laser Doppler velocimetry (LDV) and digital particle image velocimetry (DPIV) investigated the flow field generated by a pitched-blade turbine in laminar operations. Their stirrer is either paddle impeller or Rushton turbine. Therefore, it would be a very interesting experiment if we can combine the measurement of the laminar flow field in a baffled stirred tank with the DPIV technology.
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