Investigation of acoustic and geometric effects on the sonoreactor performance

In this work, three design configurations of a sonoreactor are considered under various operating conditions, and the acoustic characteristics during water sonication are investigated while using an immersed-type ultrasonic flat transducer probe in a sonoreactor model. Numerical models are also developed to simulate the sonication process, and they are successfully validated and compared with available data in the literature. Several sets of numerical investigations are conducted using the finite-element method and solved by the computational acoustics module in the COMSOL Multiphysics. The effects of the acoustical and geometrical parameters are investigated, analyzed, and reported, including the ultrasonic frequency, acoustic intensity, and scaling-up the reactor. The present study includes a parametric investigation examining the change of the ultrasonic frequency, intensity, and probe immersion depth on the performance. The results of the parametric study show that the highest cavitation energy corresponds to the maximum magnitude of negative pressure that takes place in the range of 60–80 kHz. The cavitation energy analyses are conducted under the conditions of 20 kHz of frequency and at 36 W input power. It is found that the cavitation energy of 15.87 W could produce 2.98 × 10⁻¹⁰ mol/J of sonochemical efficiency. In addition, the effect of altering the transducer probe depth changes the acoustic pressure field insignificantly. Furthermore, a recommendation is made to improve the sonochemical efficiency by introducing more considerable ultrasound input power while operating the sonoreactor at an ultrasonic frequency lower than 60 kHz. The results presented in this paper provide a comprehensive assessment of different sonoreactors and the feasibility of scaling-up their production rate.     

Indirect ultrasonication for protein quantification and peptide mass mapping through mass spectrometry-based techniques

We report in this work a fast protocol for protein quantification and for peptide mass mapping that rely on ¹⁸O isotopic labeling through the decoupling procedure. It is demonstrated that the purity and source of trypsin do not compromise the labeling degree and efficiency of the decoupled labeling reaction, and that the pH of the labeling reaction is a critical factor to obtain a significant ¹⁸O double labeling. We also show that the same calibration curve can be used for MALDI protein quantification during several days maintaining a reasonable accuracy, thus simplifying the handling of the quantification process. In addition we demonstrate that ¹⁸O isotopic labeling through the decoupling procedure can be successfully used to elaborate peptide mass maps. BSA was successfully quantified using the same calibration curve in different days and plasma from a freshwater fish, Cyprinus carpio, was used to elaborate the peptide mass maps.     

A comparative study on the modeling of sound pressure field distributions in a sonoreactor with experimental investigation

In sonochemical reactors the effect of emerging cavitation bubbles has significant influence on the amplitude and structure of the developing sound field. Calculations show that the damping parameter and the phase velocity may, depending on the pressure amplitude, change by several orders of magnitude. For example, the sound velocity in water comes to 1500 ms⁻¹, whereas in a bubbly liquid it may decrease to 20 ms⁻¹, which is much below the velocity of sound in air (about 340 ms⁻¹). In this paper, a method of calculating the time dependent three-dimensional pressure field in sonochemical reactors of various shapes is presented. It takes into account inhomogeneous distributed wave parameters which are a function of the spatial depending pressure amplitude. The modeled results are then compared with experimentally measured values of a certain kind of reaction vessel. The agreement is found to be satisfactory.     

Visualization and optimization of cavitation activity at a solid surface in high frequency ultrasound fields

Despite the increasing use of high frequency ultrasound in heterogeneous reactions, knowledge about the spatial distribution of cavitation bubbles at the irradiated solid surface is still lacking. This gap hinders controllable surface sonoreactions. Here we present an optimization study of the cavitation bubble distribution at a solid sample using sonoluminescence and sonochemiluminescence imaging. The experiments were performed at three ultrasound frequencies, namely 580, 860 and 1142 kHz. We found that position and orientation of the sample to the transducer, as well as its material properties influence the distribution of active cavitation bubbles at the sample surface in the reactor. The reason is a significant modification of the acoustic field due to reflections and absorption of the ultrasonic wave by the solid. This is retraced by numerical simulations employing the Finite Element Method, yielding reasonable agreement of luminescent zones and high acoustic pressure amplitudes in 2D simulations. A homogeneous coverage of the test sample surface with cavitation is finally reached at nearly vertical inclination with respect to the incident wave.     

The effects of liquid height/volume,initial concentration of reactant and acoustic power on sonochemical oxidation

Even though much knowledge on acoustic cavitation and its application has been accumulated over the past decades, further research is still required to develop industrial uses of acoustic cavitation. It is because the available information is mainly based on small-scale sonoreactors and the design and optimization of sonoreactors for large-scale applications have not been widely studied. In this study, the effects of liquid height/volume, initial concentration of the reactant and input acoustic power on sonochemical oxidation reactions including iodide ion oxidation, As(III) oxidation, and hydrogen peroxide generation were investigated using a 291 kHz sonoreactor with various liquid height/volumes (50, 100, 200, 300, 500, and 1000 mL) and input powers (23, 40, and 82 W). As the liquid height/volume and the input power changed, the power density varied from 23 to 1640 W/L and the maximum cavitation yields of triiodide ion for 23, 40, and 82 W were observed at 0.05, 0.1, and 0.2/0.3 L, respectively. It was found that low power was more effective for the small volume and the large volume required high power level and the moderate power density, approximately 400 W/L, was suggested for the sonochemical oxidation of iodide ion in the 291 kHz sonoreactor in this study. Similar results were observed in the generation of hydrogen peroxide and the sonochemical oxidation of As(III) to As(V). It was also revealed that KI dosimetry could be applicable for the estimation of the sonochemical reactions of non-volatile compounds such as As(III).     

An improved clean sonoreactor-based method for protein identification by mass spectrometry-based techniques

A new clean fast (8 min) method for in-solution protein digestion without detergent or urea for protein identification by peptide mass fingerprint and mass spectrometry-based techniques is proposed. The new method avoids the use of time consuming desalting procedures entailing the following four steps done under the effect of an ultrasonic field provided by a sonoreactor: denaturation (1 min) in a mixed solution of water:acetonitrile 1/1 (v/v); protein reduction (1 min); protein alkylation (1 min); and protein digestion (5 min). Five proteins with masses comprised between 14.4 kDa and 97 kDa and the protein split-soret cytochrome c from D. desulfuricans ATCC27774, were successfully identified with this procedure. No differences were found in the sequence coverage or in the number of peptides matched when the new clean method was compared to another one using urea. Twofold better signal-to-noise ratios were obtained in the MALDI spectra from protein samples prepared with the new method when comparing it with a method using urea. The new digestion method avoids the need to remove salt content and increases throughput (six samples at once) while reducing sample loss and contamination from sample handling.     

Characterisation and improvement of a reference cylindrical sonoreactor

This paper describes theoretical and experimental methods for characterising the performance of a 25 kHz sonochemical reactor (RV-25), which is being developed as a reference facility for studying acoustic cavitation at the National Physical Laboratory (NPL). Field measurements, acquired in different locations inside the sonoreactor, are compared with finite element models at different temperatures, showing that relatively small temperature variations can result in significant changes in the acoustic pressure distribution (and consequent cavitation activity). To improve stability, a deeper insight into the way energy is transferred from the power supply to the acoustic field is presented, leading to criteria - based on modal analysis - to dimension and verify an effective temperature control loop. The simultaneous use of measurements and modelling in this work produced guidelines for the design of multi-frequency cylindrical sonoreactors, also described.     

Investigation of sonochemical activities at a frequency of 334 kHz: The effect of geometric parameters of sonoreactor

In this study, the effect of the dimensions of the bottom plate and liquid height was investigated for high-frequency sonoreactors under a vertically irradiated system. The dimensions of the bottom plate did not significantly influence sonochemical activity considering power density. However, as the bottom plate was increased in size, the hydroxyl radical generation rate decreased because of a decrease in power density. It is therefore recommended that sonoreactors with bottom-plate dimensions close to those of the ultrasonic transducer module be used. Liquid height had a significant effect on sonochemical activity, but the trend of the activity considering power density changed as the initial pollutant concentration changed. In the case of low initial concentration of As(III) (1 mg/L), the maximum cavitation yield for As(III) oxidation was observed at liquid heights of 150 mm.     

Development of a fast and efficient ultrasonic-based strategy for DNA fragmentation

Several ultrasound-based platforms for DNA sample preparation were evaluated in terms of effective fragmentation of DNA (plasmid and genomic DNA)—ultrasonic probe, sonoreactor, ultrasonic bath and the newest Vialtweeter device. The sonoreactor showed the best efficiency of DNA fragmentation while simultaneously assuring no cross-contamination of samples, and was considered the best ultrasonic tool to achieve effective fragmentation of DNA at high-throughput and avoid sample overheating. Several operation variables were studied—ultrasonication time and amplitude, DNA concentration, sample volume and sample pre-treatment—that allowed optimisation of a sonoreactor-based strategy for effective DNA fragmentation. Optimal operating conditions to achieve DNA fragmentation were set to 100% ultrasonic amplitude, 100 μL sample volume, 8 min ultrasonic treatment (2 min/sample) for a DNA concentration of 100 μg mL⁻¹. The proposed ultrasonication strategy can be easily implemented in any laboratory setup, providing fast, simple and reliable means for effective DNA sample preparation when fragmentation is critical for downstream molecular detection and diagnostics protocols.     

Multi-frequency sonoreactor characterisation in the frequency domain using a semi-empirical bubbly liquid model

Recently, multi-frequency systems were reported to improve performance in power ultrasound applications. In line with this, digital prototyping of multi-frequency sonoreactors also started gaining interest. However, the conventional method of simulating multi-frequency acoustic pressure fields in the time-domain led to many challenges and limitations. In this study, a multi-frequency sonoreactor was characterised using frequency domain simulations in 2-D. The studied system consists of a hexagonal sonoreactor capable of operating at 28, 40 and 70 kHz. Four frequency combinations were studied: 28–40, 28–70, 40–70 and 28–40–70 kHz. A semi-empirical, modified Commander and Prosperetti model was used to describe the bubbly-liquid effects in the sonoreactor. The root-mean-squared acoustic pressure was compared against experimental validation results using sonochemiluminescence (SCL) images and was noted to show good qualitative agreement with SCL results in terms of antinode predictions. The empirical phase speed calculated from SCL measurements was found to be important to circumvent uncertainties in bubble parameter specifications which reduces error in the simulations. Additionally, simulation results also highlighted the importance of geometry in the context of optimising the standing wave magnitudes for each working frequency due to the effects of constructive and destructive interference.