High-shear impellers (HSIs) are mixers used in industrial stirred tanks to incorporate powders into liquids and break down particle agglomerates. A detailed numerical study of two commercial ring-style HSIs of laboratory scale was carried out and their performance was compared with the Rushton turbine (RT). It was found that power and pumping numbers or their ratio cannot be simply connected for properly selecting an impeller in applications where highly localized viscous dissipation is desirable. The ratio of the average viscous dissipation in the impeller swept volume to the mean in the entire volume at two constant values of power input turned out to be lower for HSIs compared to that evaluated for RT. However, at higher power input, the dimensionless average viscous dissipation in the blade swept volume was found to be similar for the HSI of two rings and the RT, corroborating the high local viscous dissipation of this HSI when operated at higher speeds.

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Biological control is the artificial manipulation of natural enemies of a pest for its regulation to densities below a threshold for economic damage. The authors address the biological control of a class of pest population models using a modelbased robust feedback approach. The proposed control framework is based on a recursive cascade control scheme exploiting the chained form of pest population models and the use of virtual inputs. The robust feedback is formulated considering the nonlinear model uncertainties via a simple and intuitive control design. Numerical results on three pest biological control problems show that the proposed model-based robust feedback can regulate the pest population at the desired reference via the manipulation of a biological control action despite model uncertainties.

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