Multiple impeller reactors are widely used due to their advanced gas utilization and an increased volumetric mass transfer coefficient. However, with the application of Rushton impellers, gas dispersion efficiency varies between the bottom and the upper impeller levels. The present study analyzes the individual flow regime, power input, and gas hold-up in each compartment of a reactor equipped with four Rushton impellers. The results indicate that the pre-dispersion of the air introduced by the bottom impeller (up to 80%) plays a key role in a better gas retention efficiency of the upper impellers (>300%) and leads to a shift of the cavity and flooding lines in the flow map (Fr-vs Fl-Number) of the upper impellers. A novel analysis of the bubble flow in the dispersed state via a two-phase LES-based CFD model reveals that a more homogenous distribution of air bubbles in the upper compartments leads to high compartment gas hold-up values, but fewer bubbles in the vicinity of the impellers. The measured and simulated data of this study indicate that the upper impellers' efficiency mostly depends on the flow regime of and the pre-dispersion by the bottom impeller rather than on the upper impellers' flow regimes. These results contribute to the understanding of essential mixing processes and scaling of aerated bioreactors.

In high-performance industrial fermentation processes, stirring and aeration may account for significant production costs. Compared to the widely applied Rushton impellers, axial-pumping impellers are known to yield a lower power draw and at the same time improve mixing. However, their lower gas dispersion capability requires stronger agitation, compromising these benefits. Diverse advanced impeller forms have been developed to cope with this challenge. We apply alternating radial and axial impellers and demonstrate strong gas dispersion and energy-efficient mixing for the first time in a large-scale (160 m 3 ) bioreactor, based on experimental and computational fluid dynamics simulation data. For equal operating conditions (stirrer speed, aeration rate), this setup yielded similar gas hold-ups and better mixing times (35%) compared to a classical Rushton-only configuration. Hence, applying a radial impeller on an upper level for improving gas dispersion maintains the benefits of axial impellers in terms of reducing energy demand (up to 50%). We conclude that this effect is significant only at large-scale, when bubbles substantially expand due to the release of the hydrostatic pressure and have time to coalesce. The work thus extends current knowledge on mixing and aeration of large-scale reactors using classical impeller types.

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While it is undisputed that the Eurozone crisis has contributed to the politicization of European integration, the longer-term impact of this politicization on the structure of political conflict in Europe remains unclear. This article engages with research findings which argue that the crisis has contributed to a shift of political cleavages in Europe, from an economic (left vs. right) to a transnational (pro-vs. anti-EU) divide. We examine whether there is any evidence of such a shift in parliamentary debates about the crisis in four Eurozone states (Germany, Austria, Spain and Ireland) between 2009 and 2014. We use a combination of content and cluster analysis to identify the discursive frames that parliamentarians employed to make sense of the crisis, and then assess which factors affected how these frames were used. Our findings show that the economic (left-right) cleavage remained highly influential in shaping the four parliaments' crisis discourse.

Examples of less well-known electrochemical processes will also be described, as well the possibilities of electrochemistry in the closing of material cycles. On-site processes for production of hydrogen peroxide, chlorine reduction in gas streams, and cleaning of particle systems using electrochemical processes will also be discussed. Another promising area in electrochemistry is electrodialysis. Examples of selective separation of pollutants from processes and their conversion into recyclable materials will be discussed.