Hydrodynamic cavitation-assisted preparation of porous carbon from garlic peels for supercapacitors

Numerical simulation of cavitation-vortex interaction mechanism in an advanced rotational hydrodynamic cavitation reactor

Hydrodynamic cavitation (HC), a promising technology for enhancing processes, has shown distinct effectiveness and versatility in various chemical and environmental applications. The recently developed advanced rotational hydrodynamic cavitation reactors (ARHCRs), employing cavitation generation units (CGUs) to induce cavitation, have demonstrated greater suitability for industrial-scale applications than conventional devices. However, the intricate interplay between vortex and cavitation, along with its spatial-temporal evolution in the complex flow field of ARHCRs, remains inadequately elucidated. This study investigated the interaction mechanism between cavitation and vortex in a representative interaction-type ARHCR for the first time using the "simplified flow field strategy" and the Q-criterion. The findings reveal that the flow instability caused by CGUs leads to intricate helical and vortex flows, subsequently giving rise to both sheet and vortex cavitation. Subsequently, utilizing the Q-criterion, the vortex structures are identified to be concentrated inside and at CGU edges with evolution process of mergence and separation. These vortex structures directly influence the shape and dimensions of cavities, establishing a complex interaction with cavitation. Lastly, the vorticity transport equation analysis uncovered that the stretching and dilatation terms dominate the vorticity transport process. Simultaneously, the baroclinic term focuses on the vapor-liquid interface, characterized by significant alterations in density and pressure gradients. These findings contribute to a better comprehension of the cavitation-vortex interaction in ARHCRs.

LES investigation of the wavy leading edge effect on cavitation noise

This paper investigates the noise reduction performance of biomimetic hydrofoils with wavy leading edge and the corresponding mechanisms. We employ Large Eddy Simulation (LES) approach and permeable Ffowcs Williams-Hawkings (PFW-H) method to predict cavitation noise around the baseline and biomimetic hydrofoils. The results show that the wavy leading edge can effectively reduce the high-frequency noise, but has little effect on the low-frequency noise. Further analyses and discussions deal with the noise reduction mechanisms. The main source for the low-frequency noise is the cavity volume acceleration, while the wavy leading edge has little effect on it. The high-frequency noise sources, related to the surface pressure fluctuations and the turbulence characteristics, are significantly suppressed by the wavy leading edge, thus decreasing the high-frequency noise intensity. Our investigation indicates that the wavy leading edge has great prospects for cavitation noise reduction technique.

Effect of the arrangement of cavitation generation unit on the performance of an advanced rotational hydrodynamic cavitation reactor

Hydrodynamic cavitation (HC) is widely considered a promising process intensification technology. The novel advanced rotational hydrodynamic cavitation reactors (ARHCRs), with considerably higher performance compared with traditional devices, have gained increasing attention of academic and industrial communities. The cavitation generation unit (CGU), located on the rotor and/or stator of an ARHCR, is utilized to generate cavitation and consequently, its geometrical structure is vital for the performance. The present work studied, for the first time, the effect of the arrangement of CGU on the performance of a representative ARHCR by employing computational fluid dynamics based on the "simplified flow field" strategy. The effect of CGU arrangement, which was neglected in the past, was evaluated: radial offset distance (c), intersection angle (ω), number of rows (N), circumferential offset angle (γ), and radial spacing (r). The results indicate that the CGU, with an arrangement of a low ω and moderate c, N, γ, and r, performed the highest cavitation efficiency. The corresponding reasons were analyzed by combining the flow field and cavitation pattern. Moreover, the results also exposed a weakness of the "simplified flow field" strategy which may induce the unfavorable "sidewall effect" and cause false high-pressure region. The findings of this work may provide a reference value to the design of ARHCRs.

Sonolytic degradation kinetics and mechanisms of antibiotics in water and cow milk

Antibiotics (ABX) residues frequently occurred in water and cow milk. This work aims to understand the kinetics and mechanisms of sonolytic degradation of four ABX, i.e. ceftiofur hydrochloride (CEF), sulfamonomethoxine sodium (SMM), marbofloxacin (MAR), and oxytetracycline (OTC) in water and milk. In both water and milk, the sonolytic degradation of ABX follows pseudo-first order (PFO) kinetics well (R2: 0.951-0.999), with significantly faster ABX degradation in water (PFO kinetics constants (k1): 1.5 × 10-3-1.2 × 10-1 min-1) than in milk (k1: 3.5 × 10-4-5.6 × 10-2 min-1). The k1 values for SMM degradation in water increased by 118% with ultrasonic frequency (40-120 kHz), 174% with ultrasonic frequency (80-500 kHz), 649% with ultrasonic power (73-259 W), 22% with bulk temperature (12-40℃), and by 68% with reaction volume (50-250 mL), respectively, in other things being equal. The relevant k1 values in milk increased by 326%, 231%, 122%, 10% as well as 82% with the above same effective factors, respectively. The oxidation by free radicals generated in situ dominates ABX degradation, and the hydrophobic CEF (54.0-971.7 nM min-1) and SMM (39.2-798.4 nM min-1) underwent faster degradation than the hydrophilic MAR (33.9-751.9 nM min-1) and OTC (33.8-545.3 nM min-1) in both water and milk. Adding an extra 0.5 mM H2O2 accelerated SMM degradation by 19% in water and 33% in milk. After 130-150 min sonication of 100 mL of 2.0 mg L-1 (6.62 μM) SMM in various milk with 500 kHz and 259 W, the residue concentrations (52.9-96.3 μg L-1) can meet the relevant maximum residue limit (100 μg L-1).

Ultrasound-assisted fermentation of ginkgo kernel juice by Lactiplantibacillus plantarum: Microbial response and juice composition development

This study is aimed to explore the feasibility of ultrasound on enhancing the fermentation properties of ginkgo kernel juice by Lactiplantibacillus plantarum Y2. Specifically, ultrasound at 20 kHz and different intensities (mild ultrasound intensity-84.42 W/L, moderate ultrasound intensity-115.50 W/L, high ultrasound intensity-173.88 W/L) with a pulse mode were applied to facilitate the fermentation process. The number of viable cells of Lactiplantibacillus plantarum Y2 increased by 5.06, 5.05 and 2.19% in the sonicated groups at 173.88, 115.50 and 84.42 W/L, compared with the non-sonicated juice after 24-h fermentation. Furthermore, mild intensity ultrasonication improved the permeability of the cell membrane, which is beneficial for the metabolism of phenolics, amino acids and organic acids. Ultrasonication increased in-vitro antioxidant activity of fermented ginkgo kernel juice by promoting the metabolism of phenolic acids, such as ferulic acid, chlorogenic and caffeic acids. At the end of fermentation, the sonicated group at 84.42 W/L has the maximum consumptions of total sugars and proteins (increased by 12.52 and 18.73%). Moreover, the reduction rate of the poison material 4'-O-methylpyridoxine (MPN) in ginkgo kernel juice increased by more than 16.40% with ultrasound treatment at 173.88 W/L after the fermentation for 48 h. Overall, ultrasound can improve the metabolizations of Lactobacillus plantarum and reduce the toxic substances, which promoted the nutritional value and flavors of ginkgo kernel juice.

Hybrid hydrodynamic cavitation (HC) technique for the treatment and disinfection of lake water

Water reclamation from lakes needs to be accomplished efficiently and affordably to ensure the availability of clean, disinfected water for society. Previous treatment techniques, such as coagulation, adsorption, photolysis, ultraviolet light, and ozonation, are not economically feasible on a large scale. This study investigated the effectiveness of standalone HC and hybrid HC + H₂O₂ treatment techniques for treating lake water. The effect of pH (3 to 9), inlet pressure (4 to 6 bar), and H₂O₂ loading (1 to 5 g/L) were examined. At pH = 3, inlet pressure of 5 bar and H₂O₂ loadings of 3 g/L, maximum COD and BOD removal were achieved·H₂O₂ was observed to significantly improve the performance of the HC when used as a chemical oxidant. In an optimal operating condition, a COD removal of 54.5 % and a BOD removal of 51.5 % using HC alone for 1 h is observed. HC combined with H₂O₂ removed 64 % of both COD and BOD. The hybrid HC + H₂O₂ treatment technique resulted in a nearly 100% removal of pathogens. The results of this study indicate that the HC-based technique is an effective method for removing contaminants and disinfection of the lake water.

Investigation of cavitation noise using Eulerian-Lagrangian multiscale modeling

We have employed the large eddy simulation (LES) approach to investigate the cavitation noise characteristics of an unsteady cavitating flow around a NACA66 (National Advisory Committee for Aeronautics) hydrofoil by employing an Eulerian-Lagrangian based multiscale cavitation model. A volume of fluid (VOF) method simulates the large cavity, whereas a Lagrangian discrete bubble model (DBM) tracks the small bubbles. Meanwhile, noise is determined using the Ffowcs Williams-Hawkings equation (FW-H). Eulerian-Lagrangian analysis has shown that, in comparison to VOF, it is more effective in revealing microscopic characteristics of unsteady cavitating flows, including microscale bubbles, that are unresolvable around the cloud cavity, and their impact on the flow field. It is also evident that its evolution of cavitation features on the hydrofoil is more consistent with the experimental observations. The frequency of the maximum sound pressure level corresponds to the frequency of the main cavity shedding for the noise characteristics. Using the Eulerian-Lagrangian method to predict the noise signal, results show that the cavitation noise, generated by discrete bubbles due to their collapse, is mainly composed of high-frequency signals. In addition, the frequency of cavitation noise induced by discrete microbubbles is around 10 kHz. A typical characteristic of cavitation noise, including two intense pulses during the collapsing of the cloud cavity, is described, as well as the mechanisms that underlie these phenomena. The findings of this work provide for a fundamental understanding of cavitation and serve as a valuable reference for the design and intensification of hydrodynamic cavitation reactors.

A Novel Method Based on Hydrodynamic Cavitation for Improving Nitric Oxide Removal Performance of NaClO2

In the removal of nitric oxide (NO) by sodium chlorite (NaClO2), the NaClO2 concentration is usually increased, and an alkaline absorbent is added to improve the NO removal efficiency. However, this increases the cost of denitrification. This study is the first to use hydrodynamic cavitation (HC) combined with NaClO2 for wet denitrification. Under optimal experimental conditions, when 3.0 L of NaClO2 with a concentration of 1.00 mmol/L was used to treat NO (concentration: 1000 ppmv and flow rate: 1.0 L/min), 100% of nitrogen oxides (NOx) could be removed in 8.22 min. Furthermore, the NO removal efficiency remained at 100% over the next 6.92 min. Furthermore, the formation of ClO2 by NaClO2 is affected by pH. The initial NOx removal efficiency was 84.8-54.8% for initial pH = 4.00-7.00. The initial NOx removal efficiency increases as the initial pH decreases. When the initial pH was 3.50, the initial NOx removal efficiency reached 100% under the synergistic effect of HC. Therefore, this method enhances the oxidation capacity of NaClO2 through HC, realizes high-efficiency denitrification with low NaClO2 concentration (1.00 mmol/L), and has better practicability for the treatment of NOx from ships.