Controlling extreme cavitation conditions by laser tailoring of surface functionalities (eCATS)

Controlling extreme cavitation conditions by laser tailoring of surface functionalities (eCATS) Cavitation as a physical phenomenon occurs due to a local pressure drop in the liquid and represents small gas/vapour bubbles that grow and collapse at multiple locations and can release a large amount of energy in a short span of time. Bubble collapse can be accompanied by extreme conditions such as strong shear flows, microjet formation, shock waves and high local temperatures. This usually results in unwanted effects such as erosion, efficiency loss, noise and vibrations on mechanical machines/devices. However, cavitation can also serve for intensification of various physical and chemical processes that are important in a variety of applications, such as surface cleaning, enhanced chemistry, and wastewater treatment. To exploit this enormous potential of hydrodynamic cavitation, we are already investigating fundamental mechanisms of interaction between bubbles and contaminants (bacteria and viruses) within our ERC Consolidator Grant - CABUM. Wastewater treatment and other processes that use hydrodynamic cavitation for decontamination require extreme cavitation conditions for efficient destruction of microorganisms. Consequently, a cavitation device that usually consists of a cavitation chamber, suffers from intense material loss, noise and vibrations. This problem is currently addressed by (i) modification of main geometry of the submerged body or flow tract or (ii) by selection of advanced materials with increased wear resistance. However, geometry modification results in decreased cavitation and is therefore not appropriate for inducing extreme cavitation conditions required for decontamination, while solely increased wear resistance does not allow controlling the cavitation intensity. To fill this gap and develop a new approach to generate extreme cavitation conditions with minimized erosion effects on the cavitation device, the proposed eCATS project investigates the mechanisms of interaction between different types of cavitation and laser- functionalized surfaces. To achieve this, we will combine different body geometries with functionalized surfaces. We will perform surface functionalization by laser nano- and micro-processing that we have already developed within our ARRS project (No. J2-1741) and that has been proven as one of the most promising paramount methods in the field of surface engineering. Recent studies that exploit and implement cavitation as an advanced treatment method deal mostly with the effectiveness of the method itself. Thus, they usually follow a very simplistic principle - the more intense the cavitation, the more effective the process. Most of them intentionally discard the consequences such as material erosion and durability of the cavitation device, even though these side effects significantly affect applicability. The overall eCATS objective is to improve the fundamental understanding of how surface micro-/nano-topography, chemistry, and wettability influence cavitation dynamics and cavitation erosion. This understanding will allow us to use advanced laser processing to control cavitation dynamics. We expect that the eCATS results will enable to create 3D surfaces that lead to extreme cavitation behind these surfaces, but do not lead to cavitation erosion of themselves. This is achieved in three steps, where we study the interaction between: (i) a single laser-induced bubble and flat functionalized surfaces; (ii) bubble clusters and flat functionalized surfaces; (iii) 3D laser-textured samples and hydrodynamic cavitation. In the final step, the results of the previous two steps are merged to find optimal surface functionalization techniques to control cavitation characteristics to either enhance or mitigate cavitation and its consequences.