Cavitation-induced shock wave behaviour in different liquids

Dual frequency ultrasonic liquid phase exfoliation method for the production of few layer graphene in green solvents

In this work, we implement a dual frequency (24 kHz and 1174 kHz) ultrasonic assisted liquid phase exfoliation (ULPE) technique in deionized water (DIW) and other eco-friendly solvents, to produce a variety of high-quality few-layer graphene (FLG) solutions under controlled ultrasonication conditions. The resulting FLG dispersions of variable sizes (∼0.2-1.5 μm2) confirmed by characterisation techniques comprising UV-Vis spectroscopy, Raman spectroscopy and high-resolution transmission electron microscopy (HR-TEM). For the first time we demonstrate that high yield of FLG flakes with minimal defects, stable for 6 + months in a solution (stability ∼ 70 %), can be obtained in less than 1-hour of treatment in either water/ethanol (DIW:EtOH) or water/isopropyl alcohol (DIW:IPA) eco-friendly mixtures. We also scrutinized the underlying mechanisms of cavitation using high-speed imaging synchronized with acoustic pressure measurements. The addition of ethanol or IPA to deionized water is proposed to play a central role in exfoliation as it regulates the extend of the cavitation zone, the intensity of the ultrasonic field and, thus, the cavitation effectiveness. Our study revealed that lateral sizes of the obtained FLG depend on the choice of exfoliating media and the diameter of a sonotrode used. This variability offers flexibility in producing FLG of different sizes, applicable in a wide spectrum of size-specific applications.

Numerical study of cavitation shock wave emission in the thin liquid layer by power ultrasonic vibratory machining

In the field of power ultrasonic vibration processing, the thin liquid layer nestled between the tool head and the material serves as a hotbed for cavitation shock wave emissions that significantly affect the material's surface. The precise manipulation of these emissions presents a formidable challenge, stemming from a historical deficit in the quantitative analysis of both the ultrasonic enhancement effect and the shock wave intensity within this niche environment. Our study addresses this gap by innovatively modifying the Gilmore-Akulichev equation, laying the groundwork for a sophisticated bubble dynamics model and a pioneering shock wave propagation model tailored to the thin liquid layer domain. Firstly, our study investigated the ultrasound enhancement effect under various parameters of thin liquid layers, revealing an amplification of ultrasound pressure in the thin liquid layer area by up to 7.47 times. The mathematical model was solved using the sixth-order Runge-Kutta method to examine shock wave velocity and pressure under different conditions. our study identified that geometric parameters of the tool head, thin liquid layer thickness, ultrasonic frequency, and initial bubble radius all significantly influenced shock wave emission. At an ultrasonic frequency of 60 kHz, the shock wave pressure at the measurement point exhibited a brief decrease from 182.6 to 179.5 MPa during an increase. Furthermore, rapid attenuation of the shock wave was found within the range of R0-3R0 from the bubble wall. This research model aims to enhance power ultrasonic vibration processing technology, and provide theoretical support for applications in related fields.

High-intensity ultrasound treatment of Atlantic cod: Impact on nutrients, structure, sensory quality, bioactivity, and in-vitro digestibility

This study evaluates the impact of high-intensity ultrasound (HIU) on the physicochemical properties and in-vitro digestibility of Atlantic cod (Gadus morhua). Various ultrasound durations (0-60 min) were applied to assess changes in color attributes, total antioxidant capacity (TAC), total flavonoid content (TFC), total phenolic content (TPC), total protein content, and in-vitro protein digestibility (IVPD). Results indicated HIU maximumly increased TAC, TFC, TPC, and peptide content before digestion by 7.28 % (US60), 3.00 % (US30), 32.43 % (US10), and 18.93 % (US60), respectively. While HIU reduced total protein content, it enhanced IVPD by up to 12.24 % (US30). Color attributes electron microscopy reflected structural changes in the cod samples, suggesting the effectiveness of HIU in altering protein structures. These findings highlight HIU's potential as a non-thermal technique for improving the sensory and nutritional quality of Atlantic cod, offering valuable insights for the seafood processing industry and consumers.

Ultrasonic liquid exfoliation for producing graphene materials from rice stem: Investigating cellular components and functionalities

This study investigates a prospective and straightforward method for producing graphene material derived from biomass, examining the influence of plant cell composition and functions. The experimental outcomes highlight ultrasound's crucial role in synthesizing graphene material sourced from biomass. Ultrasound, a pivotal element in the experiment, significantly affects graphene production from biomass by working synergistically with the liquid components in the solvent system. Notably, the ethanol content reduces the solution's surface tension, facilitating the effective dispersion of biochar and graphene oxide sheets throughout the process. Simultaneously, the water content maintains the solution's polarity, enhancing the cavitation effect induced by ultrasound. Biomass-derived graphene is exfoliated utilizing an ultrasonic bath system (134.4 W, 40 kHz, 0.5 W/cm2) from biochar. The as-synthesized graphene oxide exhibits a structure comprising a few layers while remaining intact, featuring abundant functional groups. Interestingly, the resulting product displays nanopores with an approximate diameter of 100 nm. These nanopores are attributed to preserving specific cell structures, particularly those with specialized cell wall structures or secondary metabolite deposits from biomass resources. The study's findings shed light on the impact of cellular structure on synthesizing graphene material sourced from biomass, emphasizing the potential application of ultrasound as a promising approach in graphene production.

Control mechanisms of different bionic structures for hydrofoil cavitation

Cavitation limits the efficient and stable operation of rotating machinery. The exploration of control methods for hydrofoil cavitation is important for improving the performance of hydraulic machinery. The leading-edge protuberances of the humpback flipper and the spine structure of the tail fin of sailfish are two common bionic structures for cavitation control; however, the control effects of both have limitations. Accordingly, in this study, a passive control method for hydrofoil cavitation was developed by combining the two bionic structures. With the large eddy simulation method, the cavitation processes of wavy leading-edge hydrofoil, bionic fin spine structure hydrofoil, and novel bionic combined structure hydrofoil were studied under a cavitation number of σ = 0.8. The control mechanisms of the three bionic structures for the hydrofoil cavitation were investigated. The results indicated that the novel bionic combined hydrofoil realised the superposition and complementation of the control effects of the two single bionic structures and achieved a better cavitation inhibition effect, reducing the total volume of cavitation by 43 %. In addition, it enhanced the stability of the flow field and reduced the standard deviation of the pressure coefficient on the suction surface by up to 46.55 %. This research provides theoretical support for the optimisation and modification of the blades of hydraulic machinery, such as propellers and pump turbines.