CD Laboratory for Cavitation and Micro Erosion

The subject of the research is mechanical micro-erosion caused by a liquid. The mechanisms, approaches and techniques of such erosion caused by cavitation and the impact of droplets or jets of liquid on solid surfaces are investigated in detail.

Cavitation is the formation of gas bubbles in a liquid caused by negative pressure, for example in strong ultrasonic fields. If such gas bubbles collapse, extreme conditions - with high pressure values and temperatures - can occur briefly inside them and on neighbouring surfaces. This attacks and erodes even the hardest materials. Droplets hitting surfaces can also develop great erosion potential, which is a desired reaction in certain cases. Accordingly, the concept of erosion is defined so broadly here that, in addition to "destruction", "cleaning" by gentle interaction of liquid or cavitation bubbles with the solid surfaces is also investigated.

The research work is initially focussing on the mechanical processes at the micro level. They are triggered when droplets hit or cavitation bubbles pulsate on a solid object and then collapse. While a lot is already known in this area for smooth surfaces, we are also interested in contaminated and structured surfaces, which have hardly been investigated to date. The aim is to achieve controlled erosion or cleaning activity by specifically influencing and selecting external parameters, such as the droplet size or the ultrasonic field. Knowledge of the exact microscopic phenomena is the prerequisite for optimising the erosion effects. Thanks to the research work, it is possible to treat solid surfaces and structures precisely and in a scalable manner, for example to clean them without destroying them.

The extreme conditions in a collapsing bubble are also the basis for many other phenomena and techniques associated with cavitation. Various chemical reactions take place inside the bubble (sonochemistry), which are also investigated. Under certain conditions, for example, light is also produced (sonoluminescence). In addition, strong currents and turbulence occur in the liquid, which not only serve cleaning purposes, but also mixing processes or disinfection. Many of the processes involved are not yet fully understood in detail. The research results are highly relevant for cavitation applications in the fields of cleaning, chemistry, medicine or life sciences.