Emulsification mechanism in an ultrasonic microreactor: Influence of surface roughness and ultrasound frequency

Numerical analysis of dynamic acoustic resonance with deformed liquid surfaces: the acoustic fountain

“…At 20 • C the cavitation pressure is in the range from 16 MPa to 30 MPa (Herbert et al 2006, p. 041603-4), and it is found to decrease monotonically with temperature: from 26 MPa at 0.1 • C to 17 MPa at 80 • C. Furthermore, the authors highlight the importance of water purity, as the cavitation threshold varies largely depending on impurities and gas content. A similar experimental study using a 1 MHz focused transducer was carried out by Vlaisavljevich et al (2016), in which the decrease of cavitation pressure with temperature was confirmed: from 29.8 MPa at 10 • C to 14.9 MPa at 90 • C. Figure 11 summarises the different acoustic pressure thresholds for water at 1 MHz as a function of temperature, allowing us to distinguish the different phenomena. The atomisation VOF and Faraday instability curves were computed using the Kumar & Tuckerman (1994) method and the modified Goodridge formula using a value of 0.9 for the constant (see the Appendix C), respectively.…”

“…The Faraday instability and atomisation thresholds were converted into an acoustic pressure using the relation between the particular oscillation u (in m) and the acoustic pressure (in Pa) from (2.2). Based on the works of Herbert et al (2006) andVlaisavljevich et al (2016) the cavitation threshold of water at 1 MHz is in the range of 24-28 MPa at 20 • C. As a consequence, cavitation bubbles should appear during a resonance peak. The strong peak obtained for the Magnitude 11 simulation (see figure 9a), has an acoustic pressure above 25 MPa.…”

“…The atomisation VOF and Faraday instability curves were computed using the Kumar & Tuckerman (1994) method and the modified Goodridge formula using a value of 0.9 for the constant (see the Appendix C), respectively. For this, the temperature dependence of surface tension, density, speed of sound and shear viscosity was implemented using the values reported in Vlaisavljevich et al (2016Vlaisavljevich et al ( , p. 1066. The Faraday instability and atomisation thresholds were converted into an acoustic pressure using the relation between the particular oscillation u (in m) and the acoustic pressure (in Pa) from (2.2).…”

“…Ultrasound-assisted microreactors have proven to be relevant for various applications in biological, pharmaceutical and chemical processes (Fernandez Rivas & Kuhn 2016;Suryawanshi et al 2018;Dong et al 2021). High intensity acoustic fields enable non-invasive manipulation of fluids and solids, which can for example be exploited to enhance fluid mixing in microreactors, to generate nanoemulsions (Modarres-Gheisari et al 2019;Udepurkar, Clasen & Kuhn 2023) and to achieve controlled atomisation in ultrasonic nebulisers to produce fine chemicals and pharmaceuticals (Naidu, Kahraman & Feng 2022). Focused ultrasound can also be used to enhance drug delivery through the fragmentation of drug carriers and the enhancement of nanoparticle penetration in the region of interest, see e.g.…”

A Liquid Mirror Resonator

“…Interfacial tension and capillary waves are relevant to a variety of microfluidic systems, among them compound droplets [ 1 ], liquid interfaces [ 2 ], emulsification mechanisms [ 3 ], droplets coalescence [ 4 , 5 ], microfluidic devices [ 6 ], bioreactors [ 7 ], bifluid flows [ 8 ], microjets [ 9 ], and particle separation [ 10 ]. In a seemingly unrelated lane of study, optical microfluidics [ 11 , 12 ] have been used for biological and chemical analysis [ 13 , 14 , 15 , 16 ] as well as for biolasers [ 17 ].…”