Hydrodynamic cavitation in microfluidic devices with roughened surfaces

The importance of the hydrodynamic cavitation phenomenon in small domains has been increasing during recent decades along with the global demand for microfluidic devices involving small-scale cavitation applications. Different characteristics of microscale hydrodynamic cavitation relative to the conventional size can be exploited in futuristic applications and improvements in the performances of new-generation microfluidic devices. Therefore, in-depth studies on the fundamentals of microscale hydrodynamic cavitation are required to reveal new physics of small-scale hydrodynamic cavitation. In this study, microfluidic devices with rough surfaces and micro restrictive elements are fabricated so that a basic study on 'Hydrodynamic Cavitation on Chip' is performed. Cavitating flows are investigated under transient and fully developed turbulent conditions within the Reynolds number range between 2962 and 8620 and cavitation number range between 2.025 and 0.72. The microfluidic devices have short restrictive elements with hydraulic diameters of 75, 66.6 and 50 µm and lengths of 2 mm, which are connected to a bigger microchannel with a width of 900 µm and length of 2 mm, called an 'extended channel'. Different upstream pressures up to 900 Psi are applied at the inlet. The hydrodynamic cavitation inception is recorded and analyzed for each microfluidic device. Flow patterns are characterized inside the microfluidic devices from cavitation inception to chocked flow conditions. Accordingly, it is observed that the transition from inception to choked occurs slowly in contrast to microscale hydrodynamic cavitation results in the literature under laminar flow conditions. Moreover, the comparison between microfluidic devices with roughened and plane (smooth) surfaces reveals that the roughened surface results in more intense cavitating flows, especially at higher upstream pressures relative to the plane surface. (paper)