Mechanically Stirred Vessels

Particle suspension in top-covered unbaffled tanks

“…As a matter of fact, it is well known that for single-phase baffled tanks equipped with Rushton turbines, power number increases with an increase in impeller clearance (Hemrajani and Tatterson, 2004). In the present case the distance of the impeller from tank bottom is significantly modified by the presence of unsuspended particles, especially at high solid loading.…”

Mass transfer and hydrodynamic characteristics of a high aspect ratio self-ingesting reactor for gas–liquid operations

“…The relatively constant value observed may anyway be regarded as an indication of hydrodynamic robustness. It is finally worth noting that if each of the six stirrers dissipated the same power as if they were placed in a standard stirred vessel, then the relevant power numbers would have been 4 for the radial impeller (Bates et al, 1963) and 1.27 for each of the axial impellers (Hemrajani and Tatterson, 2004), and the total dissipation by the six stirrers would have resulted in an ungassed power number (based on the larger impeller diameter) of 4.94. The fact that about the same value was obtained here for the six impeller system may be regarded as a validation of the experimental procedure adopted.…”

Modeling of Oxygen Transfer Correlations for Stirred Tank Bioreactor Agitated with Atypical Helical Ribbon Impeller

“…Inferior k L a values below 800 W m −3 for helical screw compared to others may be attributed to the absence of horizontal turbine disc or baffles structure. The spinning disk helps to create lower pressure region in bioreactor to redirect the bubbles passage into the high shearing region of the blades while baffles can create additional breakup near the tank wall areas [2] . Nevertheless as the power input increases, the energy dissipated by the close clearance geometry could have created higher turbulence throughout the stirred tank environment and increases the liquid drag force.…”

“…Open type impellers have from one third to half of D i /D T ratio. Else, if the diameter ratio is higher or as found in some setup, quite close to the vessel wall to effect a scraping action, impellers are otherwise generalized as proximity type agitators [2] . Open type are primarily employed in aerobic fermentation whereas proximity types are mostly associated with the bulk blending of viscous nonNewtonian fluids [3] .…”