Ultrasonic Atomization Research Articles

A Comparative Study on Laser Powder Bed Fusion of Differently Atomized 316L Stainless Steel.

The significant growth of Additive Manufacturing (AM), visible over the last ten years, has driven an increase in demand for small gradation metallic powders of a size lower than 100 µm. Until now, most affordable powders for AM have been produced using gas atomization. Recently, a new, alternative method of powder production based on ultrasonic atomization with melting by electric arc has appeared. This paper summarizes the preliminary research results of AM samples made of two AISI 316L steel powder batches, one of which was obtained during Ultrasonic Atomization (UA) and the other during Plasma Arc Gas Atomization (PAGA). The comparison starts from powder particle statistical distribution, chemical composition analysis, density, and flowability measurements. After powder analysis, test samples were produced using AM to observe the differences in microstructure, porosity, and hardness. Finally, the test campaign covered an analysis of mechanical properties, including tensile testing with Digital Image Correlation (DIC) and Charpy’s impact tests. A comparative study of parts made of ultrasonic and gas atomization powders confirms the likelihood that both methods can deliver material of similar properties.

Sustainability-driven optimization of ultrasonic atomization-assisted micro milling process with ceramic matrix composite

The micro milling of ceramic matrix composites poses huge challenges in machining process as the anisotropic characteristic, strength-to-weight ratio and high cutting temperature. Apart from that, the emission and disposal of lubrication liquids have a negative impact on the environment conservation. In order to acquire better machinability of ceramic matrix composites, a new micro milling technique integrated with ultrasonic atomization based on water-based lubricating agent and coolant is presented in this work. Correspondingly, the novel sustainability-driven optimization framework of machining parameters is developed for the proposed ultrasonic atomization-assisted micro milling operation. The integration criteria of sustainability assessment with manufacturing process and machined product have been investigated in the technical, economic and environmental aspects, in which tool remaining useful life, stochastic machining process variables, surface quality of machine product, machining cost and carbon emission are included. The estimation accuracy of the related sustainability criteria are validated with a series of machining conditions. The proposed tool remaining useful life prediction method can significantly improve the ultimate life of micro cutting tool, the average prediction errors of cutting forces, energy consumption and surface roughness are 11.83%, 9.60% and 11.02%, meanwhile, the machining cost and carbon emission can also be reduced with ultrasonic atomization lubrication compared to those under flood fluids. Then, on the basis of the overall sustainability criteria, the multi-objective optimization framework is carried out to obtain the optimal machining parameters with the improved cuckoo search methodology, wherein the dimensionality of multiple variables is reduced by the principal component analysis. The comparison results about preferred and optimal machining parameters, and the related radial diagram of integral sustainability performance index validate that the sustainability performance of ultrasonic atomization-assisted micro milling operation could be enhanced by the proposed comprehensive optimization framework. The developed sustainability-driven optimization system offers a basis for the sustainable micro manufacturing technique of difficult-to-cut composite materials.

Use of High-Frequency Ultrasound Waves for Boiler Water Demineralization/Desalination Treatment

Isolated ultrasonic vibrations were used to treat feed water from a 20 bar steam-producing water tube boiler. Physical treatments such as ultrasounds and reverse osmosis (RO) are recommended as the most eco-friendly for this purpose. A novel bench-scale prototype delivering 6 L/h of treated water was designed and built. The ultrasonic atomization of raw water with 1.7 MHz piezoelectric transducers and subsequent humidification and dehumidification of drag airflow was the innovating sequence of operations used as a treatment technique. To ensure greater humidification capacity to the drag air, the energy available from the thermal inertia of the liquid column (raw water) in the prototype vaporization chamber was used to heat this air flow. After a single pass of raw water through the bench-scale prototype, a 98.0% reduction in conductivity and a 99.0% decrease in the content of total dissolved solids were obtained at a drag air temperature of 70 °C. Compared to RO, two of the main advantages of the proposed ultrasonic wave method are the elimination of the use of chemical agents in the pre-treatment phase and a significant reduction in maintenance costs by membrane replacement.

Improving the flexibility and durability of aged paper with bacterial cellulose

Ancient paper with irreplaceable value was severely acidified and aged due to poor storage conditions and the degradation of its own components. The restoration of ancient paper in deacidification and reinforcement was imperative. Bacterial cellulose (BC) with good fiber aspect ratio and rich hydroxyl groups was suitable to enhance aged paper. However, the utilization of BC for paper reinforcement was limited with its dispersion due to the highly aggregated state. In this paper, stable BC solutions were prepared by dissolving BC in NaOH/urea, and its application in ancient paper restoration by ultrasonic atomization was proposed. BC was uniformly bridged on the fiber surface and between the fibers, which played a good role in strengthening the aged paper. After treatment, the mechanical strength of the paper was notably improved, the paper processed for 60 min using 0.6% BC solution exhibited a high folding resistance of 28 times, which was 2.15 times of the untreated paper. Besides, the pH value and alkali reserves of the repaired paper were successfully achieved at 8.12 and 0.4 mol/kg. Even after hot-humid aging for 30 d, the repaired paper retained about 50% of its initial strength. This suggested the repair fluid based on BC had potential applications in the field of paper reinforcement with high performance and durability.

Supercapacitors based on nitrogen-enriched crumpled graphene with a high volumetric capacitance and high-mass-loading per area of the electrode

The low volumetric capacity and sluggish diffusion of ions at high mass loadings of active materials per area limit any improvement of the energy and power densities of supercapacitors. A mixture of graphene oxide (GO) and urea in water was treated by an ultrasonic atomizer to form aerosol droplets, which were dried to obtain crumpled GO/urea particles. Crumpled graphene with a nitrogen content of 11.38% was obtained by the thermal shocking of these particles at 600 °C for 50 s. A volumetric capacitance of 384.0 F cm−3 was achieved when the crumpled graphene was used as supercapacitor electrodes. Even at a high current density (10 A g−1) and a high loading (74.3 mg/cm2 electrode), the specific capacitance retention still remained high. It is proposed that N-doping in the forms of pyrrole, imide, lactam and other types of pyridine-like nitrogen, and high surface area of the sample were key factors in improving the capacitance. The crumpled structure provided high mass transfer and high accessibility of ions to the active surface.

Development, verification and application of a versatile aerosol calibration system for online aerosol instruments

Traditional calibration methods mostly focus on the calibration of detection systems while the calibration from the sampling and pre-condition systems to the detection system is usually ignored. In this regard, a Primary Standard Aerosol Mass Concentration Calibration System (PAMAS) is developed for the whole-process calibration of time-resolved aerosol measurement instruments. PAMAS is composed of a particle generation chamber, an ultrasonic atomizer, a dilution system, and a syringe pump. It is designed to steadily generate standard aerosol particles of known concentrations (≤250 μg/m3), chemical compositions, and stable particle size distributions. Monodispersed aerosol can be generated in the size range of hundreds of nanometers to several micrometers with a narrow size distribution. The generated particles with different compositions generated by PAMAS have been well verified by the filter-based gravimetric method, yielding accuracy and R2 of more than 95% and 0.999 in a wide concentration range. The response time by changing the target concentration of reference particles is 1–2 min. PAMAS has been applied to various types of time-resolved aerosol measurement instruments, including particle mass concentration monitors (Beta Attenuation and Tapered Element Oscillating Microbalance), online Ion Chromatograph, and semi-continuous OCEC carbon aerosol analyzer. Very consistent results between PAMAS and calibrated instruments can be obtained if the instruments are functioning well. As for instruments with certain technical issues, PAMAS can serve as a good tool for performance evaluation and quality assurance of the instruments and the accuracy of the measurement data can be adjusted based on the calibration results.

Aerosol therapy during mechanical ventilation in intensive care units: A questionnaire-based survey of 2203 ICU medical staff in China

BackgroundTo describe the current status of aerosol therapy during mechanical ventilation (MV) and the practice, knowledge, and beliefs about aerosol therapy in physicians working in the intensive care unit (ICU) in China. MethodsA physician self-administered questionnaire-based cross-sectional survey was carried out from January 2019 to July 2019. An electronic questionnaire was designed, and physicians who worked regularly in ICUs across several hospitals were contacted through WeChat. Answers to all questions and the general characteristics of physicians who answered the questionnaire were collected and analyzed. ResultsA total of 2203 medical staff who regularly worked in the ICUs completed this questionnaire (9.0% missing data); 87.7% of the participants were doctors. Most respondents claimed that they often administered aerosolization therapy. Ultrasonic atomizer (50.7%) and jet nebulizer (48.6%) were the most commonly used atomization devices. Bronchodilators (65.8%) and steroids (66.3%) were the most frequently aerosolized drugs during MV. During nebulization, ventilator settings were never changed by 32.7% of respondents. Only 49.1% of respondents knew the appropriate place for a nebulizer. Further, 62.7% of respondents using heated humidifiers reported turning them off during nebulization. Specific knowledge about droplet size and nebulization yield was poor. Respondents from tertiary hospitals and those with higher technical title or work experience tended to have better accuracy than those from primary hospitals or with lower technical titles (P < 0.050). ConclusionsAerosol therapy was commonly used during MV, and the most frequent drugs were bronchodilators and steroids. Scientific knowledge about the optimal implementation of aerosol therapy during MV seemed deficient.

Insights on the effectiveness of pneumatic and ultrasonic atomization in combination with UVC light for processing of fruit juices.

This study evaluated the effectiveness of spraying juices, during shortwave ultraviolet irradiation (UVC) treatments as an alternative to promote more contact area, by means of ultrasonic atomization (UA) and pneumatic atomization (PA). Four juices with dissimilar physical characteristics were processed to assess the effect of suspended solids and turbidity. Antioxidant activity, anthocyanins, ascorbic acid, and inactivation of Saccharomyces cerevisiae inoculated in the juices were evaluated. Five decimal reduction cycles were reached after two passes of orange or grapefruit juice through the UVC + UA arrangement. On the other hand, five decimal reduction cycles were achieved after three passes in the UVC + PA arrangement. Losses of 11% and 14% of ascorbic acid were observed in orange and grapefruit juice, respectively, while anthocyanin content presented losses of 50% and antioxidant activity decreased by 40% for pomegranate and blueberry juice, correspondingly.

Effect of the area of a lithium niobate transducer on the efficiency of ultrasonic atomization driven by resonance vibration

In recent years, individual control of one’s personal environment has been drawing increasing attention due to the growing interest in health care. Wearable devices are especially useful because of their controllability regardless of location. Humidity is one of the inevitable factors in the personal environment as a preventive against infectious diseases. Although atomization devices are commonly used as a method of humidity control, at present, there are no wearable humidity control devices. Vibration of a lithium niobate (LN) device in the thickness mode is a promising piezoelectric method for miniaturization of atomization devices for humidity control. To miniaturize the atomization device, the transducer size needs to be small not so much as to decrease the atomization efficiency. However, the effect of the device area on the atomization efficiency of LN at a size suitable for mounting in wearable devices has not been studied. Here, we conducted an atomization demonstration of LN devices with different sizes to evaluate particle size and atomization efficiency. Furthermore, to reveal the relationship between vibration behavior and atomization efficiency, resonance vibration in the MHz frequency band was evaluated by the finite element method and an impedance analyzer. The results showed that the peak size of water particles atomized by each device was in the range of 3.2 to 4.2 µm, which is smaller than particles produced by typical piezoelectric ceramics. Moreover, the best LN size for efficient atomization was found to be 8 mm × 10 mm among the five LN device sizes used in experiments. From the relationship between vibration behavior and atomization efficiency, the size of the transducer was suggested to affect the vibration mode. The obtained result suggested that the LN device is suitable for small wearable nebulizer devices.

Seaweed-like Nitrogen-Doped Porous Carbon Superstructures via an Ultrasonic Atomization Ice Template as High-Performance Electrodes in Supercapacitors

Seaweed-like Nitrogen-Doped Porous Carbon Superstructures <i>via</i> an Ultrasonic Atomization Ice Template as High-Performance Electrodes in Supercapacitors

Revisiting the Effect of the Air-Water Interface of Ultrasonically Atomized Water Microdroplets on H2O2 Formation.

Studying chemical processes at the air-water interface is always challenging. A recent report claimed that H2O2 was formed spontaneously on the surface of condensed water microdroplets. However, a newer report concluded that the detected H2O2 in the previous report could originate in part from the water vapor source that involved ultrasonic atomization of liquid water. Here, this phenomenon is reinvestigated regarding the influence of ultrasonic cavitation, surface modification of droplets, and solutes in the bulk liquid on H2O2 production. When the droplet surfaces were modified by surfactants, H2O2 production did not change, whereas adding gases or inorganic compounds to the bulk solution caused significant changes in H2O2 production. These results confirm that H2O2 formation originates from cavitation in bulk solutions. It is concluded that the air-water interface of water microdroplets itself does not generate H2O2.

Parameter optimization of ultrasonic vibration polishing K9 optical glass based on ultrasonic atomization

To further improve the surface finish and processing efficiency of optical components, ultrasonic vibration technology is frequently combined with conventional processing and the process parameters that play a critical role in this composite processing are identified. This research proposes an ultrasonic vibration polishing method based on ultrasonic atomization (UA-UVP). The polishing performance of K9 optical glass is increased by ultrasonic atomization (UA) assisted by polishing solvent for ultrasonic vibration polishing (UVP). Orthogonal experiments are used to study the effects and variation laws of the flow rate of ultrasonic atomization (Q), the gap distance between the polishing tool and workpiece (G), ultrasonic electro spindle speed (W), abrasive particle size (D) and ultrasonic amplitude (A) on surface roughness (SR) and material removal rate (MRR), respectively. When these two polishing characteristics are considered together, the optimization of polishing parameters becomes complicated. Therefore, the principal component analysis (PCA) and grey relational analysis (GRA) methods were employed to the optimal experimental combination as Q:18 ml/min, G: 5 μm, W: 4000 r/min, D: 0.5 μm, A: 8 μm. The experimental results showed that Ra and MRR were measured as 10.466 nm and 0.473*10^8 μm3/min, respectively. Compared with the best experimental combination of orthogonal experiments, the improvement rates of SR and MRR were 26.65% and 25.80%, respectively. Overall, the application of ultrasonic vibration technology contributes to enhancing the uniform distribution of polished abrasive particles and improving the polishing characteristics.

Periodicity in ultrasonic atomization involving beads-fountain oscillations and mist generation: Effects of driving frequency

Ultrasonic atomization induced by high driving frequency, generally on the order of 1 MHz or higher, could involve a liquid fountain in the form of a corrugated jet, or a chain of “beads” of submillimeter diameter in contact. This study concerns dynamics/instability of such beads fountain, observed under lower input power density (≤ 6 W/cm2) of the “flat” ultrasound transducer with a “regulating” nozzle equipped, exhibiting time-varying characteristics with certain periodicity. High-speed, high-resolution images are processed for quantitative elucidation: frequency analysis (fast Fourier transform) and time–frequency analysis (discrete wavelet transform) are employed, respectively, to evaluate dominant frequencies of beads-surface oscillations and to reveal factor(s) triggering mist emergence. The resulting time variation in the measured (or apparent) fountain structure, associated with the recurring-beads size scalable to the ultrasound wavelength, subsumes periodic nature predictable from simple physical modeling as well as principle. It is further found that such dynamics in (time-series data for) the fountain structure at given height(s) along a series of beads would signal “bursting” of liquid droplets emanating out of a highly deformed bead often followed by a cloud of tiny droplets, or mist. In particular, the bursting appears to be not a completely random phenomenon but should concur with the fountain periodicity with a limited extent of probability.

Design and development of ultra-sensitive, dynamically stable, multi-modal GnP@MXene nanohybrid electrospun strain sensors

Electrospun fiber-based strain sensors are widely used in biomonitoring due to their network construction and tailorable design. However, poor cycling stability and lack of multi-modality remain major issues. In this study, a 3-component material system consisting of MXene, graphene nanoplatelets (GnPs), and cellulose nanocrystals (CNCs) was employed to address multi-modality and sensitivity shortcomings. The hybrid synergetic interactions between MXene and graphene nanoplatelets (GnPs) provided high gauge factors (400 at 100% and 76.1 at 10% strains). Smaller and more conductive MXene particles provided higher electrical conductivity and sensitivity at lower strain ranges (with a low detection limit of 0.25% and a short response time of 100 ms) by forming localized brittle regions. Synergistically, GnP flakes with large laterial sizes promoted network connectivity, easy sliding across larger strains, and lubricity. On the other hand, the CNC binder enhances the uniformity and interfacial hydrogen bonding between the constituents, leading to desirable cycling capabilities for over 2,000 cycles. An in-situ ultrasonic atomization process was used to decorate the poly(styrene–butadienestyrene) (SBS) substrate with the electrically conductive additives, which remarkably enhanced the uniformity of the conductive coating. With the simultaneous vacuum-assisted filtration, this technique provided more conformal and in-depth fiber decoration, promoting multi-modality and sensitivity. The developed strategies proved to be effective in creating sensors with ideal body integration and successful recording of various body motions.

Enrichment of amino acids from its aqueous solution by ultrasonic atomization and ultrafine bubbles

The enrichment characteristics of amino acids by ultrasonic atomization were investigated. Samples were aqueous solutions of L-phenylalanine and L-tyrosine. The ratio of amino acid concentration in the mist to that in the solution was defined as the enrichment factor. As the flow rate of carrier gas became higher, the collection mass of mist increased and the enrichment factor decreased. The enrichment factor depended on the solution pH. The enrichment factor increased with decreasing amino acid concentration in the solution and enhanced by the addition of ultrafine bubbles.

Faraday instability of a liquid layer in ultrasonic atomization

Ultrasonic atomization is increasingly used in industry, and the theory of Faraday instability in this process is investigated and compared with experiments and multiple Faraday wave simulations. For the viscosity-free case, the parametric curve equations explain the excitation and competition mechanisms of the different frequency harmonics and determine the strength of the Faraday instability. In the viscous case, the Faraday instability depends on the wavenumber and viscosity, and the strength of the instability can be obtained from the instability threshold. This study can provide scientific guidance for the process optimization of practical ultrasonic atomization production.

Acoustic cavitation detection during ultrasonic atomization process

An assembly was carried out to experimentally determine the absence of acoustic cavitation during free surface ultrasonic atomization, which occurs when a liquid is gradually deposited on a surface that vibrates with an amplitude greater than the atomization threshold.The detection system developed, capable of detecting incipient cavitation during the process, is based on the digital processing of a PVDF piezoelectric transducer signal, attached to the surface of the tip of an ultrasonic atomizer.During the experiments carried out, it was not possible to detect acoustic cavitation during free surface ultrasonic atomization. Therefore the hypothesis about the influence of acoustic cavitation in the atomization process described has not been confirmed.The experimental system developed could be used to monitor free surface acoustic atomization processes, to keep the system in optimal operation. When these atomization systems are over the liquid flux limit, can cause accumulation at the tip, which could generate fountain-type atomization, which has different atomization characteristics.

Performance improvement of tubular solar still using nano-coated hanging wick thin film, ultrasonic atomizers, and cover cooling

Three modifications were applied, in steps, on tubular solar still (TSS) to enhance its performance. First, three ultrasonic atomizers were placed under a hanging wick tent. Second, to enhance the thin-film evaporation from the wick layer, Cobalt Oxide nanoparticles (NP-Co3O4) were added to the hanging wick coating so that it could enhance the heat transfer and thermal properties. Finally, a cover cooling unit was integrated with the modified TSS (MTSS) to degrade the cover temperature and enhance vapor condensation. Besides, the cooling could increase the temperature difference between the wick and the cover to improve the free convection process. Comparison between the MTSS and conventional TSS (CTSS) was investigated in terms of some parameters, such as freshwater output, thermal energy efficiency, total heat transfer coefficient, and exergy efficiency. The results showed that the freshwater productivity was enhanced by 28, 59.2, and 82.5%, for the cases' order, respectively. The best case was TSS with the third modification (nanocoated hang wick, atomizers, and cover cooling), in which, the thermal efficiency, total heat transfer coefficient, and exergy efficiency were improved by 68.14, 40.5, and 119.1%. Moreover, a cost analysis was carried out on the three cases, which revealed that the maximum saving in freshwater price was 39.14%.

Effect of a Metallocene Catalyst Mixture on CNT Yield Using the FC-CVD Process

This work studies synthesis of carbon nanotube (CNT) sheet using the high temperature (1400 °C) floating catalyst chemical vapor deposition (FC-CVD) method. Three metallocenes—ferrocene, nickelocene, cobaltocene—and their combinations are used as precursors for metal catalysts in the synthesis process. For the carbon source, an alcohol fuel, a combination of methanol and n-hexane (9:1), is used. First, the metallocenes were dissolved in the alcohol fuel. Then, the fuel mixture was injected into a tube furnace using an ultrasonic atomizer with Ar/H2 carrier gas in a ratio of about 12/1. The synthesis of CNTs from a combination of two or three metallocenes reduces the percentage of metal catalyst impurity in the CNT sheet. However, there is an increase in structural defects in the CNTs when using mixtures of two or three metallocenes as catalysts. Furthermore, the specific electrical conductivity of the CNT sheet was highest when using a mixture of ferrocene and cobaltocene as the catalyst. Overall, the multi-catalyst method described enables tailoring certain properties of the CNT sheet. However, the standard ferrocene catalyst seems most appropriate for large-scale manufacturing at the lowest cost.

Faraday wave instability characteristics of a single droplet in ultrasonic atomization and the sub-droplet generation mechanism

Compared with the traditional mechanical atomization technology, ultrasonic atomization technology has been widely used in industry in recent years because of its higher energy efficiency and environmental friendliness. However, the physical mechanism of ultrasonic atomization of the individual droplet has not been studied, especially the evolution of Faraday instability and the formation mechanism of sub-droplets, leading to a lack of scientific theoretical guidance for the application of this technology. Here, we observed different Faraday wave patterns and evolution processes on the surface of the individual droplet using high-speed camera technology. The wettability of the droplet is significantly enhanced by the vibration effect. Interestingly, the Faraday waves of highly viscous droplets show multiple concentric semicircular ripple shapes. Droplet atomization is the result of Faraday wave mode transition and instability evolution induced by inertial forces, and both viscosity and surface tension play a suppressive role in the development of Faraday instability. The vibration frequency of stable Faraday waves was traced, and the effects of amplitude, surface tension, viscosity, and liquid volume on the Faraday wave wavelength and number were investigated. The characteristic parameters of Faraday wave instability evolution such as atomization amplitude threshold and atomization time were investigated under different experimental conditions. It is found that for low-viscosity liquids, the atomization amplitude threshold depends mainly on the surface tension, while for high-viscosity liquids, the atomization amplitude threshold is influenced by both viscosity and liquid volume. The effects of surface tension, viscosity, and volume on the atomization time are similar to those on the atomization amplitude threshold. We investigated the kinetic process of sub-droplet generation and showed that differences in Rayleigh-Plateau instability and capillary pinch-off mechanisms lead to different patterns of sub-droplet generation, where the former depends on the capillary number threshold and the latter can be divided into the protrusion break mode and the ligament break mode. The proportion of these two modes was investigated under different experimental conditions to quantitatively evaluate the selectivity of the mother droplet atomization mode. For the first time, the dispersion distribution of the sub-droplets was explained by using the length and number characteristics of the ligaments. The correlation analysis of sub-droplet size on ligament length and ligament number was established, and a linear fitting function was obtained.