Contact

Dr. Hendrik Hessenkemper

h.hessenkemperAthzdr.de
Phone: +49 351 260 4719

Experiment: Lateral lift force of single bubbles

The shear-induced lift force, which strongly influences the spatial bubble distribution, is one of the most important non-drag forces. However, measuring the lift force of ellipsoidal bubbles in a shear field is a very challenging task. Recently, our group developed a special experimental design that allows creating a stable linear shear field in air-water systems. Together with an averaging procedure suitable to address irregular movements of bubbles with high Reynolds number, we were able to experimentally determine the lift coefficient of ellipsoidal bubbles. Furthermore, we could reveal how surfactants and even tiny amounts of impurities in tap water can alter the strength of the lift force.

Left: Experimental design to create linear shear flow. Right: Averaging procedure to obtain average bubble rise path.

Foto: Lift corr ©Copyright: Dr. Hendrik Hessenkemper

Lift coefficient for different modified Eötvös numbers of ellipsoidal bubbles in water.

Ongoing work: Wall effects on the lift force

With regard to the hydrodynamic rising behavior of gas bubbles, it is known that additional acting forces or a modification of acting forces such as the drag force or the lift force can occur near the wall. Previous studies have focused on spherical bubbles or on highly viscous systems. In our current work, we want to investigate such phenomena for ellipsoidal/deformable bubbles in low-viscosity systems, as in the previous experiments on the lift force. In particular, modifications of the shear-induced lift force due to wall effects will be investigated.

Ongoing work: Swarm effects on the lift force

A particular focus of our work is the investigation of swarm effects, which are caused by the interaction of bubbles and their surrounding flow field with other bubbles in the vicinity. By implementing and applying AI-based evaluation methods, experimental images with an increased number of bubbles can be evaluated automatically. We will use these methods to investigate the aforementioned phenomena with bubble swarms, since bubble swarms, in contrast to single bubbles, can be found in most practical cases.

Publications