Engineering characterization of the novel Bach impeller for bioprocessing applications requiring low power inputs

The choice of impeller design in stirred-tank reactors (STRs) affects important process characteristics such as the suspension of particulates, mixing of nutrients or gasses, and the distribution of turbulent kinetic energy and its dissipation rate. A novel impeller, the Bach impeller, has been characterized in this work and its novel geometry and mechanism of action are discussed in detail. Experimental measurements of the power consumption, mixing time, and microparticles suspension dynamics were carried out at the 1 L scale in an unbaffled reactor and the performance compared with two conventional up-pumping axial flow impellers, namely the 3-Blade segment (3BS, also called “elephant ear”) and marine impeller. In addition, the impeller flow number and pumping efficiency were obtained from Particle Image Velocimetry experiments. The Bach impeller exhibited a low power number of NP=0.36 and showed it can generate a uniform suspension of microcarriers even at relatively low impeller speeds (from N=25–30 rpm onwards). The impeller was found to effectively mix the reactor volume within tM=25 s at N>50 rpm (i.e. NtM=37±5) at a higher clearance when it was mounted closer to the free surface, C/T>0.5, while minimally affecting its suspension capabilities. Lastly, the Bach impeller displaced more fluid than the marine impeller and roughly an equal amount to the 3BS impeller, suggesting that the novel impeller can successfully be used for STR processes in the (bio)chemical engineering industry where low power inputs, but high mixing and particle suspension efficiencies are sought.

Duke Scholars

Author Seog Oh Physics