Intensity Of Ultrasonic Field Research Articles

PLASMA AND CHEMICAL SYNTHESIS OF ZINC OXIDE NANOPARTICLES UNDER THE INFLUENCE OF NONLINEAR CAVITATION EFFECTS

This work examines the properties of zinc oxide nanoparticles obtained in plasma discharge under the influence of ultrasound and by the deposition method. It has been shown that special form of plasma discharge in a liquid in an intensive ultrasonic field above the cavitation threshold can be effectively used to produce zinc oxide nanoparticles. The resulting sample consists of individual particles or their small associates ranging from 30 to 60 nm in size and aggregates of these particles with a wide range of sizes. Additional exposure to ultrasound allows to obtain particles with average size of less than 20 nm. The deposition method produces larger hexagonal particles with a size of 40 nm and a length of up to 100 nm. This difference is explained by the shorter growth time of crystals in plasma discharge.

Modelling of ultrasonic vibration-assisted forming considering the distribution of ultrasonic field with structure deformation

Ultrasonic vibration-assisted (UVA) forming is typically used to promote the forming quality of complex structures due to the acoustic-plastic effect. Ultrasonic vibration (UV) is always applied via the contact of tools with the structure surface; thus a distribution of ultrasonic field exists owing to the propagation and attenuation of ultrasonic waves, which may vary with structural deformation. This makes the prediction and control of ultrasonic effect extremely difficult in achieving high forming quality. To develop a new coupling model considering the interaction between ultrasonic field and deformation field, UVA tensile experiments of superalloy sheet were performed first. The experimental results demonstrated that UV had a local effect on the tensile specimen, resulting in non-uniform distribution of temperature, strain and dislocation density. During the modelling, the intensity of ultrasonic field was quantified by acoustic energy density, which can be calculated using vibration velocity. A dislocation-based constitutive relation was also established, in which ultrasonic-related functions were introduced to reflect the effect of ultrasonic field on structural deformation. Then, a sequential coupling modelling method was proposed. Through the cyclic calculation of ultrasonic field and deformation field, the simulation of UVA forming considering the distribution of ultrasonic field with structure deformation was realised. With the coupling model, the non-uniform distribution of deformation accompanied by a non-uniform ultrasonic field during UVA forming was revealed. When applied to a complex W-bending process, the targeted softening effect on the W-bending specimen was precisely predicted. The coupling model is expected to lay a foundation for the optimisation and control of the UVA forming process.

Synthesis of gaseous hydrogen and nanoparticles of silicon and silicon oxide by pyrolysis of tetraethoxysilane in an electric discharge under the action of ultrasound

In this work, we studied the process of synthesis of gaseous hydrogen, as well as silicon and silica nanoparticles under the action of intensive ultrasonic cavitation in a plasma discharge in a tetraethoxysilane medium.It is shown that a new form of plasma discharge arising in a liquid in an intensive ultrasonic field above the cavitation threshold, characterized by a volumetric glow in the entire space between the electrodes and falling volt-ampere characteristics, can be effectively used to initiate various physical and chemical processes. It was shown that ultrasonic action in combination with an electric discharge is capable to decompose tetraethoxysilane molecules with the formation of hydrogen, carbon oxides, and also solid-phase products - silicon and silica nanoparticles.Experiments on the production of hydrogen and nanoparticles were carried out on a special experimental setup for the implementation of a plasma discharge in liquid-phase media. The setup consists of an ultrasonic generator, a piezoceramic transducer, a discharge power source, a reaction chamber, and discharge electrodes.The results of the analysis of gaseous reaction products by gas chromatography show that during the pyrolysis of liquid tetraethoxysilane, hydrogen with a content of about 90% and carbon oxides are formed. The synthesized silicon and silica nanoparticles were isolated and studied using the methods of physicochemical analysis - infrared spectroscopy, X-ray phase analysis and transmission electron microscopy to determine the composition, shape and size of nanoparticles.The study of nanoparticles by electron microscopy showed that particles of a corner shape are obtained during the synthesis. The size of the synthesized nanoparticles is 50–100 nm. It was also shown by electron microscopy that, upon aggregation, the particles do not become larger in size, but form composite associates. It is also important to note that the advantage of this method for the synthesis of nanoparticles is their activated surface, which has a high reactivity as a result of exposure to intense ultrasound.The resulting nanoparticles and their agglomerates can also be used as functional materials, fillers, and components of composite materials.

Dual-frequency multi-angle ultrasonic processing technology and its real-time monitoring on physicochemical properties of raw soymilk and soybean protein

To improve the soybean protein content (SPC), flavor and quality of soymilk, the effects of dual-frequency ultrasound at different angles (40 + 20 kHz 0°, 40 + 20 kHz 30°, 40 + 20 kHz 45°) on physicochemical properties and soybean protein (SP) structure of raw soymilk were mainly studied and compared with the conventional single-frequency (40 kHz, 20 kHz) ultrasound. Furthermore, the intensity of the ultrasonic field in real-time was monitored via the oscilloscope and spectrum analyzer. The results showed that 40 + 20 kHz 45° treatment significantly increased SPC. The ultrasonic field intensity of 40 + 20 kHz 0° treatment was the largest (8.727 × 104 W/m2) and its distribution was the most uniform. The emulsifying stability of SP reached the peak value (233.80 min), and SP also had the largest particle size and excellent thermal stability. The protein solubility of 40 + 20 kHz 30° treatment attained peak value of 87.09%. 20 kHz treatment significantly affected the flavor of okara. The whiteness and brightness of raw soymilk treated with 40 kHz were the highest and the system was stable. Hence, the action mode of ultrasonic technology can be deeply explored and the feasibility for improving the quality of soymilk can be achieved.

Applying ultrasonic fields to separate water contained in medium-gravity crude oil emulsions and determining crude oil adhesion coefficients

Separating produced water is a key part of production processing for most crude oils. It is required for quality reasons, and to avoid unnecessary transportation costs and prevent pipework corrosion rates caused by soluble salts present in the water. A complicating factor is that water is often present in crude oil in the form of emulsions. Experiments were performed to evaluate the performance of ultrasonic fields in demulsifying crude oil emulsions using novel pipe-form equipment. A horn-type piezoelectric ultrasonic transducer with a frequency of 20 kHz and power ranging from 80 W to 1000 W was used for experimental purposes. The influences of the intensity of ultrasonic fields, ultrasonic irradiation time, and the initial water content of crude oils were evaluated to establish the rate of water segregation from oil. The experiments applied ultrasonic-field intensities of 0.25 W/cm3, 0.5 W/cm3, 0.75 W/cm3 and 1 W/cm3 to synthetic emulsions with 10%, 15%, 20%, and 25% of the water in crude oil. Crude oil demulsification occurred for each ultrasonic field intensity tested for all the samples tested. Function β involving adhesion coefficients was expressed in terms of wave-field intensity and initial concentration of water in each of the three crude oil samples tested. The experiments demonstrated that despite the absence of any chemical demulsifier involved, water separation caused by applying ultrasonic fields was effective and occurred rapidly. As the intensity of the ultrasonic field applied increased, the amount of water segregated from crude oil also increased. Subjected to constant field intensity, higher initial water cuts (up to 15% or so) in the crude oil samples and higher ultrasonic irradiation times, resulted in greater segregation of water from crude oil in percentage terms. However, in samples with initial water cuts of 20+% long irradiation times (~5 min), resulted in a decline in water separation compared to 2-min tests. Ultrasonic field treatments offer commercially-viable and environmentally-friendly alternatives to treatments using chemical demulsifiers as they reduce desalination requirements of wastewater.

Electric Discharge in Liquids under the Effect of Vibration

In this study, plasma discharge in liquids at intensive ultrasonic field above the cavitation threshold has been proven to be of great interest for initiation of various physical and chemical processes. The feature of arc discharge in liquid media is the localization of plasma region near the electrodes and “falling” form of volt-ampere characteristics. In the region of intensive cavitation, the fraction of gas-vapor component in the liquid exists, therefore it can be assumed that the electric breakdown in the cavitation region should become easier, which can result in the initiation of various forms of discharges.

Biogas Generation from Sonicated Excess Sludge

The article presents an analysis of the possibilities of biogas production in the process of methane fermentation of sonicated excess sludge. The greater the percentage of methane in biogas, the higher its calorific value. In order to increase the intensity of biogas production containing approximately 70% of methane, sewage sludge is disintegrated. In particular, excess sludge formed as a result of advanced wastewater treatment by the activated sludge method shows low biodegradability. The study aim was to examine the effect of the ultrasonic field disintegration of excess sludge on biogas production. As a result of subjecting the sludge to disintegration by ultrasonic field, there was an increase in the digestion degree of sewage sludge. In the methane fermentation process of modified sludge, an increase of the biogas yield was noted, which confirmed the supportive action of ultrasonic field on the excess sludge biodegradation. In the case of disintegration of excess sludge by ultrasonic field, for the ultrasonic field intensity value of 4.3 W cm−2 and a sonication time equal to 300 s, the highest values of soluble chemical oxygen demand (SCOD), total organic carbon (TOC), and volatile fatty acids (VFAs) concentrations were obtained. In the process of conventional methane fermentation, biogas yield value was 0.303 L g VSS−1, while in the process of methane fermentation of sonicated excess sludge, the value 0.645 L g VSS−1.

Synthesis of Metal-Based Nanoparticles by Acoustoplasma Discharge for Energy Storage Applications

In this study, plasma discharge in a liquid at intensive ultrasonic field above the cavitation threshold has been proven to be of great interest for initiation of various physical and chemical processes. In such discharge, nanoparticles of tungsten and zinc oxides have been synthesized. Further exploration of synthesized nanoparticles has demonstrated that the factor of ultrasonic cavitation during the synthesis substantially affects physical and chemical characteristics of nanoparticles.

Oscillation and Migration of Bubbles within Ultrasonic Field**Supported by National Natural Science Foundation of China under Grant Nos 51327901, 51727803 and 51571164, the NPU Excellent Personnel Supporting Project, the Fundamental Research Fund of Northwestern Polytechnical University under No 3102018jcc039, and the Key Research Plan in Shanxi Province (2018GY-104).

The oscillation and migration of bubbles within an intensive ultrasonic field are important issues concerning acoustic cavitation in liquids. We establish a selection map of bubble oscillation mode related to initial bubble radius and driving sound pressure under 20 kHz ultrasound and analyze the individual-bubble migration induced by the combined effects of pressure gradient and acoustic streaming. Our results indicate that the pressure threshold of stable and transient cavitation decreases with the increasing initial bubble radius. At the pressure antinode, the Bjerknes force dominates the bubble migration, resulting in the large bubbles gathering toward antinode center, whereas small bubbles escape from antinode. By contrast, at the pressure node, the bubble migration is primarily controlled by acoustic streaming, which effectively weakens the bubble adhesion on the container walls, thereby enhancing the cavitation effect in the whole liquid.

An Improved Phased Array Ultrasonic Testing Technique for Thick-Wall Polyethylene Pipe Used in Nuclear Power Plant

With the application of high-density polyethylene (HDPE) pipe with thick wall in nuclear power plant (NPP), great attention has been paid to the safety of the pipeline joints, which can be assessed by phased array ultrasonic testing (PAUT). PAUT creates constructive interference of acoustic waves to generate focused beams according to delay law based on time-of-flight. However, due to the existence of acoustic attenuation and dispersion, waveform distortion occurs when ultrasonic pulse propagates in HDPE, which will accumulate with the increase of propagation distance, and then results in imaging errors. In this paper, the relationship between acoustic attenuation and dispersion in HDPE was obtained by numerical simulation in Field II®, which can be verified by the experiment of our previous work. Then, the investigation of the waveform distortion revealed the linear relation between peak offset and propagation distance. Considering the relation, an improved delay law was proposed to increase the intensity of ultrasonic field. This improved delay law was compared with the conventional one by numerical simulation of ultrasonic field and PAUT experiments, which showed that the improved delay law could increase the image sensitivity.

CERAMIC NANOSTRUCTURES OBTAINED BY ACOUSTOPLASMA TECHNIQUE

In this study, plasma discharge in a liquid in an intense ultrasonic field above the cavitation threshold has been proven to be of great interest for initiating various physical and chemical processes. In such a discharge, nanoparticles of tungsten and zinc oxides have been synthesized. Further exploration of synthesized nanoparticles has demonstrated that the factor of ultrasonic cavitation during the synthesis substantially affects the physical and chemical characteristics of nanoparticles. An important feature is the pronounced difference between the luminescence intensity of the particles obtained without ultrasonic treatment and the particles obtained in plasma under ultrasonic treatment: the higher intensity of particle luminescence in the case of ultrasonic action during the synthesis can be attributed to the numerous defects in the crystal structure and may be advantageous in view of possible applications for creating optically active materials.

Study of acoustoplasma discharge as a technique for synthesis of optically active materials

In this study, plasma discharge in a liquid at intensive ultrasonic field above the cavitation threshold has been proven to be of great interest for initiation of various physical and chemical processes. In such discharge, nanoparticles of tungsten and zinc oxides have been synthesised. Further exploration of synthesised nanoparticles has demonstrated that the factor of ultrasonic cavitation during the synthesis substantially affects physical and chemical characteristics of nanoparticles.

Experimental and theoretical study of crude oil pretreatment using low-frequency ultrasonic waves

In this work, an ultrasound experimental setup was designed to investigate the feasibility of using low-frequency ultrasonic waves as a substitute to reduce the consumption of chemical demulsifiers in the pretreatment of crude oil. The experiments were planned to study the effects of irradiation time, ultrasonic field intensity and initial water content on the efficiency of separation. The results of experiments showed that by selecting a proper irradiation time and field intensity, it is possible to decrease the usage of demulsifiers by 50%. Moreover, a population balance model was proposed to explicate the experimental data. A hybrid coalescence model was developed to determine the frequency of aggregation. The parameters of the model were estimated by linear regression. The parameter estimation was performed using a parallel execution of the particle swarm optimization algorithm. The results of the model showed a decent agreement with the experimental data.

Finite Element Simulation and Experimental Study of Cylindrical Focusing Piezoelectric Transducers

The possibility is considered of inducing high intensity ultrasonic fields in an oil-filled cylindrical volume using a radially polarized hollow cylindrical transducer. Conditions for forming standing cylindrical waves within the studied volume are established. Finite element simulations of the abovementioned transducer are performed along with its experimental study.

Synthesis and properties of nanocomposites of WO3 and exfoliated g-C3N4

Abstract The nanocomposites of WO3 nanoparticles and exfoliated graphitized C3N4 (g-C3N4) particles were prepared and their properties were studied. For this purpose, common methods used for characterization of solid samples were completed with dynamic light scattering (DLS) method and photocatalysis, which are suitable for study of aqueous dispersions. The WO3 nanoparticles of monoclinic structures were prepared by a hydrothermal method from sodium tungstate and g-C3N4 particles were prepared by calcination of melamine forming bulk g-C3N4, which was further thermally exfoliated. Its specific surface area (SSA) was 115 m2 g−1. The nanocomposites were prepared by mixing of WO3 nanoparticles and g-C3N4 structures in aqueous dispersions acidified by hydrochloric acid at pH = 2 followed by their separation and calcination at 450 °C. The real content of WO3 was determined at 19 wt%, 52 wt% and 63 wt%. It was found by the DLS analysis that the g-C3N4 particles were covered by the WO3 nanoparticles or their agglomerates creating the nanocomposites that were stable in aqueous dispersions even under intensive ultrasonic field. Using transmission electron microscopy (TEM) the average size of the pure WO3 nanoparticles and those in the nanocomposites was 73 nm and 72 nm, respectively. The formation of heterojunction between both components was investigated by UV–Vis diffuse reflectance (DRS) and photoluminescence (PL) spectroscopy, high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), photocatalysis and photocurrent measurements. The photocatalytic decomposition of phenol under the LED source of 416 nm identified the formation of Z-scheme heterojunction, which was confirmed by the photocurrents measurements. The photocatalytic activity of the nanocomposites decreased with the increasing content of WO3, which was explained by shielding of the g-C3N4 surface by bigger WO3 agglomerates. This study also demonstrates a unique combination of various characterization techniques working in solid and liquid phase.

Theoretical Calculations and Numerical Modeling of High Intensity Ultrasonic Fields for Optimization of High Intensity Focused Ultrasound Transducers

Objectives: This work focuses on development of the mathematical models and theoretical research of the ultrasound ablation system in respect of the calculation of High Intensity Focused Ultrasonic Fields and modeling of biological tissue heating. Methods: Theoretical calculations of acoustic fields in linear approximation were made using Rayleigh integral. For description of nonlinear High Intensity Ultrasonic Fields, finite-difference modeling of Westervelt and Khokhlov–Zabolotskaya–Kuznetsov (KZK) equations were used. Findings: Theoretical and numerical models of High Intensity Focused Ultrasound (HIFU) Transducers were developed. The results of theoretical modeling of HIFU Transducers were presented. The characteristics of High Intensity Ultrasonic Fields, including the acoustic pressure, intensity and heat sources at different excitation modes of Ultrasound Transducers were calculated. Numerical solutions of the Khokhlov–Zabolotskaya–Kuznetsov (KZK) parabolic equation were obtained for nonlinear Focused Ultrasonic Fields. The obtained results were discussed. Applications/Improvements: The obtained results can be used in the development of HIFU Transducers for Medical Ultrasound Ablation Complexes, for the treatment of socially significant diseases.

Acoustoplasma Technique for Obtaining of Metal-Based Nanostructures

In this study, plasma discharge in a liquid at intensive ultrasonic field above the cavitation threshold has been proven to be of great interest for initiation of various physical and chemical processes. In such discharge, nanoparticles of tungsten and zinc oxides have been synthesized. Further exploration of synthesized nanoparticles has demonstrated that the factor of ultrasonic cavitation during the synthesis substantially affects physical and chemical characteristics of nanoparticles.

Ultrasound assisted solidification process of ternary Cu–Sn–Sb alloy

It is well-known that the application of ultrasound during liquid to solid transitions for alloys can refine the solidification microstructure and thus improves the mechanical properties. However, most published work focuses on single phase dendritic growth, whereas little has been conducted on the multiphase alloys with complicated phase transformations during solidification. In this work, the solidification process of ternary Cu40Sn45Sb15 alloy was realized within intensive ultrasonic field with a resonant frequency of 20kHz and ultrasound power from 0W to 1000W. The ultrasound refines the size of the primary ε(Cu3Sn) intermetallic compound by two orders of magnitudes. If the ultrasound power increases to 1000W, η(Cu6Sn5) phase nucleates and grows directly from parent liquid phase without the occurrence of peri-eutectic reaction on the top of the alloy sample where the ultrasound intensity is sufficiently high. These microstructural variations lead to the enhancement of compressive strength and elasticity modulus of ternary Cu40Sn45Sb15 alloy.

The role of acoustic cavitation in liquid pressurization in narrow tubes

The liquid pressurization mechanism in narrow tubes as a result of high intensity ultrasonic field along the irradiation direction is discussed, with a focus on the physical behavior of acoustic cavitation bubbles formed at the tube's open end. The acoustic energy dissipated at the surface of the bubbles results in radiation pressure with a second harmonic frequency (2f). We show here that during the phenomenon, which resembles the functioning an ultrasonic pump, cyclical pressure fluctuations with the second harmonic frequency 2f are observed using a high-response pressure transducer. The maximum value of accumulating pressure is equivalent to the positive peak of the sound pressure in the tube without acoustic cavitation. It can be thought that the cyclic collapse and expansion of acoustic cavitation bubbles at the tube's open end contribute to the control of the inrushing sound pressure. In particular, the transmission behavior of the received pressure in a viscous liquid containing gas bubbles with high number density near the tube's open end (a quantity that is related to the kinematic viscosity of the medium liquid) plays an important role in this pressure accumulation mechanism. A dynamic model of this pressurization phenomenon is also discussed.

Ultrasound assisted deposition of silica coatings on titanium

We present a novel ultrasound assisted method for silica coating of titanium surfaces. The coatings are formed by “smashing” silica nanoparticles onto activated titanium surface in solution using intense ultrasonic field. Homogeneous silica coatings are formed by deposition of dense multiple layers of silica nanoparticles. Since the nanoparticles also grow during the reaction, the layers of the coatings have smaller particles on the substrate and larger particles towards the surface. The thickness of the coatings can be controlled with several experimental parameters. Silica layers with thickness over 200nm are readily obtained.