Small-Scale Phenomena in Reactive Bubbly Flows: Experiments, Numerical Modeling, and Applications

Improving the yield and selectivity of chemical reactions is one of the challenging tasks in paving the way for a more sustainable and climate-friendly economy. For the industrially highly relevant gas–liquid reactions, this can be achieved by tailoring the timescales of mixing to the requirements of the reaction. Although this has long been known for idealized reactors and time- and space-averaged processes, considerable progress has been made recently on the influence of local mixing processes. This progress has become possible through joint research between chemists, mathematicians, and engineers. We present the reaction systems with adjustable kinetics that have been developed, which are easy to handle and analyze. We show examples of how the selectivity of competitive-consecutive reactions can be controlled via local bubble wake structures. This is demonstrated for Taylor bubbles and bubbly flows under technical conditions. Highly resolvednumerical simulations confirm the importance of the bubble wake structure for the performance of a particular chemical reaction and indicate tremendous potential for future process improvements.

Improve of Unsteady Pressure Pulsation Based On Jet-Wake Suppression for a Low Specific Centrifugal Pump

In this study, three impellers with different blade pressure side (PS) profiles were designed and the influence on the hydraulic and dynamic performance of a low specific speed centrifugal pump was investigated by numerical simulation and experimental research. The result shows that blade PS modification introduced in this study can efficiently alleviate the unsteady pressure pulsation of pump. In order to study the effects of blade modification on the internal flow filed, the volute domain was replaced by an even outlet region for CFD analysis. Relative velocity distribution was extracted to visualize the three-dimensional (3-D) flow characteristics at the impeller outlet. The result shows that the flow at impeller outlet presents a typical jet-wake structure which is significantly suppressed after the blade modification. The suppression of jet-wake structure, which is attributed to the redistribution of pressure and velocity in the impeller caused by the change of blade work capacity can directly reduce the intensity of pressure pulsation in the volute by increasing the velocity uniformity at impeller outlet. Given that the existence of jet-wake flow results in large mixing loss and velocity deviation at the impeller outlet, entropy generation rate and slip velocity calculation were introduced here to measure the extent of jet-wake configuration. Result shows that both indicators introduced here can be used to quantify the extent of the wake-jet structure at impeller outlet, and thus, indirectly predict the strength of unsteady pressure pulsation in pump volute.