A fountain type ultrasonic atomizer was chosen to be a possible device to be used to assist in the alleviation of global warming. Atomization of seawater by an ultrasonic atomizer will enhance more cloud condensation nuclei; as a result, more UV radiation will be reflected back into the space. There are two crucial spray characters: droplet size and the number of droplets. The droplet size needs to be in a certain size range, so that they can stay in the atmosphere. The number of droplets needs to be as high as possible; the more cloud nuclei, the more UV radiation is reflected. The characteristics of sprays are affected by many parameters: liquid properties and the atomizer design. In this study, we characterized two different atomizers: one with a fixed frequency atomizer at 1.72 MHz and one with adjustable frequency and voltage atomizer with a calculated resonant frequency of 2.24 MHz. In addition for the fixed atomizer, different liquid media: tap water (20° C), hot water (46° C), cold water (14° C) and salt waters with different percents salinity (2% - 3.5% by volume), were studied. A Phase Doppler Anemometer was used to measure the characteristics of sprays: droplet velocity, droplet size and number of droplets in a required size range. It was found that the droplet velocity is barely affected by the liquid properties and liquid depth except for the hot water. The relatively high temperature liquid appears to alter the characteristics of the piezo disk; in addition, the inconsistent temperature could vary the characteristics of the spray. The droplet size is strongly dependent on liquid properties and frequency of vibration. The number of droplets is obviously affected by liquid properties and atomizer designs; there is not yet a known correlation between the number of droplets and other parameters. A theoretical study was undertaken in order to compare predicted acoustic properties of acoustic waves with the measured number of droplets generated. The mathematical model was constructed based on applying boundary conditions to a general 2- Dimensional wave equation in cylindrical coordinates. The predicted results satisfy the boundary conditions very well. Since we deal with high frequency acoustic waves, the number of wave modes used in the prediction is significant. It is important to be ensure that all the cut-on wave modes are included otherwise the predicted results will not be very accurate. The more modes that are included, the more computer storage is required; therefore, the number of modes need to be enough to obtain accurate result but not too many to be over the limit of computer storage. The high number of modes used also decreases computer speed, increasing the running time. The mathematical model was used to predict acoustic properties. It was found that the predicted maximum acoustic pressure inside the central small region, where the disk is located, has the best correlation with the number of droplets for all liquid media and all operating conditions. The mathematical model can only predict which operating condition and atomizer design will provide the maximum acoustic pressure. As a result, we can optimize the fountain type ultrasonic atomizer in order to obtain the best result, suiting each application applied. If the geometry is changed, the model is also required to be re-written so that it will predict accurate results.

This study focuses on the design and development of a new spray applicator design utilizing effects of imposed pressure oscillations in conjunction with cavitation collapse energy to create distribution of fine droplets. An oscillating horn placed inside the nozzle performing high frequency oscillations is envisioned to provide the necessary pressure perturbations on the exiting liquid jet, while the nozzle geometry design in configured to amplify cavitation process. Initially, a two-zone approach modeling the nozzle interior and exterior in a separate fashion and later, a coupled strategy is proposed. Parametric studies describing the effect of horn stroke length, frequency, its position inside the nozzle in combination with different nozzle designs and liquid flow rates are explored to identify their contribution in obtaining desired cavitation characteristics. In this regard, incorporation of a backward facing step profile within the nozzle shows strong capability of generating the required cavitation and flow field distribution at the nozzle exit. The velocity modulations occuring at the nozzle exit due to oscillating horn structure result in a wide gamut of liquid structures specific to the imposed oscillation frequency and modulation amplitude. The disintegration characteristics of these modulated liquid jets are studied using a Volume-of-Fluid (VOF) interface capturing approach based on finite volume methodology employing an interface compression scheme. VOF methods are validated against experimental results and then subsequently used to study scaling parameters governing the modulated liquid jets. To perform coupled interior-exterior nozzle computations with cavitation, two new cavitation models are presented: First, a model based on Homogeneous Equilibrium assumptions for tracking cavitation events in a compressible framework is presented. Owing to its inability to simulate incompressible cavitating flows, a new cavitation event tracking model based on a Cavitation-Induced-Momentum-Defect (CIMD) correction approach is formulated utilizing a scalar transport model for vapor volume fraction with relevant transport, diffusion and source terms. Validations of both the models against experimental observations are detailed. Coupled internal-external liquid flow computations from the proposed atomizer design using a VOF-CIMD strategy shows strong potential for rapid drop formation in the presence of cavitation effects. A prototype model of a new spray applicator design is presented.

The literature on atomization of melts has been reviewed. Models have been developed and applied to analyze the phenomena associated with centrifugal atomization of melts using rotating disk method. Some suggestions and guidelines for the development and operation of a centrifugal atomizer have been given. Previous experiments of melt atomization and present observations of water disintegration at the edge of a rotating disk have confirmed that the disintegration of melts or water occurs in one of three basic modes: direct droplet formation (DDF), ligament formation (LF) and film formation (FF). Wave theories have been used to analyze the disintegration of melts in the different regimes. The equations for the fastest growing wave number have been derived. Models for the calculation of powder particle sizes have been suggested and the calculated results have compared with available experimental data in the literature. Calculations have shown that disk diameter and disk rotating speed are two very important atomizing parameters. The type of melt and melt superheat also affect the powder particles size. In general, fine powder particles can be obtained by increasing disk rotating speed and using large diameter disk, provided that the melt does not solidify on the disk. In the DDF regime waves forming at the periphery of a disk are responsible for the break up of melts. The fastest growing wave number depends on the disk speed, disk diameter and properties of melt. In the FF regime sheet wave theory of Dombrowski and Johns was used to study the collapse of the melt sheet. The fastest growing wave number is a complex function of the speed and thickness of film and the properties of melt and atomizer atmosphere. The effects of disk diameter, disk rotating speed and melt flow rate on atomization are achieved through influencing the speed and thickness of film. The studies on the flow of melts on rotating disks have shown that the film forming on the disk was very thin, about tens of microns and the tangential velocity of melts was much higher than the radial velocity. The analysis of heat transfer of melts on a rotating disk has shown that partial solidification of melts on the disk is possible. To obtain a good atomization condition it is necessary to control the partial freezing of melts on the disk. A large melt superheat and a high melt flow rate are required to prevent melts from freezing on the disk. The use of a small diameter disk can also avoid freezing of the melt on the disk. Combining the calculations of heat transfer on the disk with the prediction of wave theory for particle sizes, it is shown that a disk of small diameter rotating at high speed is desirable for the production of fine powders. The cooling ability obtained by centrifugal atomization using the rotating disk method depends on the design of atomizer, the operating conditions and the type of material to be atomized. A large diameter disk on which solidification of melt is avoided and a high disk rotating speed result to the formation of fine powder particles which experience a high cooling rate. The nucleation undercooling of melt depends on particle size, disk speed, material to be atomized and the nucleation condition. A small particle size and a high disk speed lead to a large undercooling. The times for the completion of solidification of powder particle of typical sizes produced by centrifugal atomization have been calculated and their effects on the atomizer vessel diameter have been discussed.

A quartz multiatomizer with its inlet arm modified to serve as a trap (trap and atomizer device) was employed to trap the tin hydride and subsequently to volatilize collected analyte species with atomic absorption spectrometric detection. Generation, atomization and preconcetration conditions were optimized and analytical figures of merit of both on-line atomization as well as preconcentration modes were quantified. Preconcentration efficiency of 95 ± 5 % was found. The detection limits reached were 29 and 143 pg ml-1 Sn, respectively, for 120 second preconcentration period and on-line atomization mode without any preconcentration. The interference extent of other hydride forming elements (As, Se, Sb and Bi) on tin determination was found negligible in both modes of operation. The applicability of the developed preconcentration method was verified by Sn determination in a certified reference material as well as by analysis of real samples. Key words HG-AAS, multiatomizer (multiple microflame quartz tube atomizer), trap and atomizer device, tin determination, stannane, in atomizer trapping, interference study

The focus of this dissertation is the development of a fundamental understanding of the acoustics and piezoelectric transducer governing the operation of piezoelectric inkjets and horn-based ultrasonic atomizers when utilizing high viscosity working fluids. This work creates coupled, electro-mechanical analytical models of the acoustic behavior of these devices by extending models from the literature which make minimal simplifications in the handling terms that account for viscous losses. Models are created for each component of the considered fluid ejectors: piezoelectric transducers, acoustic pipes, and acoustic horns. The acoustic pipe models consider the two limited cases when either the acoustic boundary layer or attenuation losses dominate the acoustic field and are adapted to account for changes in cross-sectional area present in acoustic horns. A full electro-mechanical analytical model of the fluid ejectors is formed by coupling the component models using appropriate boundary conditions. The developed electro-mechanical model is applied to understand the acoustic response of the fluid cavity alone and when combined with the transducer in horn-based ultrasonic atomizers. An understanding of the individual and combined acoustic response of the fluid cavity and piezoelectric transducer allow for an optimal geometry to be selected for the ejection of high viscosity working fluids. The maximum pressure gradient magnitude produced by the atomizer is compared to the pressure gradient threshold required for fluid ejection predicted by a hydrodynamic scaling analysis. The maximum working fluid viscosity of the standard horn-based ultrasonic atomizer and those with dual working fluid combinations, a low viscosity and a high viscosity working fluid to minimize viscous dissipation, is established to be on the order of 100mPas. The developed electro-mechanical model is also applied to understand the acoustic response of the fluid cavity and annular piezoelectric transducer in squeeze type ejectors with high viscosity working fluids. The maximum pressure gradient generated by the ejector is examined as a function of the principle geometric properties. The maximum pressure gradient magnitude produced by the ejector is again compared to the pressure gradient threshold derived from hydrodynamic scaling. The upper limit on working fluid viscosity is established as 100 mPas.

abstract: A new theoretical model was developed utilizing energy conservation methods in order to determine the fully-atomized cross-sectional Sauter mean diameters of pressure-swirl atomizers. A detailed boundary-layer assessment led to the development of a new viscous dissipation model for droplets in the spray. Integral momentum methods were also used to determine the complete velocity history of the droplets and entrained gas in the spray. The model was extensively validated through comparison with experiment and it was found that the model could predict the correct droplet size with high accuracy for a wide range of operating conditions. Based on detailed analysis, it was found that the energy model has a tendency to overestimate the droplet diameters for very low injection velocities, Weber numbers, and cone angles. A full parametric study was also performed in order to unveil some underlying behavior of pressure-swirl atomizers. It was found that at high injection velocities, the kinetic energy in the spray is significantly larger than the surface tension energy, therefore, efforts into improving atomization quality by changing the liquid's surface tension may not be the most productive. From the parametric studies it was also shown how the Sauter mean diameter and entrained velocities vary with increasing ambient gas density. Overall, the present energy model has the potential to provide quick and reasonably accurate solutions for a wide range of operating conditions enabling the user to determine how different injection parameters affect the spray quality. / Dissertation/Thesis / M.S. Aerospace Engineering 2013

Orientador: Marco Aurelio Zezzi Arruda / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-09T03:57:40Z (GMT). No. of bitstreams: 1 Klassen_Aline_M.pdf: 4690770 bytes, checksum: a9edf74063589d6c5e00414205c9b518 (MD5) Previous issue date: 2007 / Resumo: Nesta Dissertação foi avaliada a eficiência do atomizador metálico (liga INCONEL600®) na técnica de HG-AAS (do inglês, hydride generation atomic absorption spectrometry) . A dissertação está dividida em três Capítulos sendo cada um referente ao desenvolvimento da metodologia para determinação de As, Bi e Se, respectivamente. Foram avaliadas variáveis físicas e químicas por meio do uso de soluções de referência de 50 mg L para As e Bi, e de 400 mg L para Se. Dentre estas variáveis podemos citar: concentração de ácido (exceto no caso do Se, em que a concentração foi mantida em 7 mol L), de NaBH4 e de NaOH, comprimento do reator, alça de amostragem, vazão de solução carregadora, vazão de gás de arraste, diâmetro interno do capilar cerâmico entre outros. Alguns parâmetros analíticos foram obtidos, respectivamente para As, Bi e Se: limite de detecção (LD), ( 2,3; 0,7; 1,8 mg L), desvio padrão relativo (RSD), (5,8; 2,7; 10%) e coeficiente de regressão (R), (0,9978; 0,9997; 0,9974). O desvio padrão relativo do método foi baseado nas réplicas das amostras. Posteriormente, foi realizado um estudo de possíveis concomitantes na determinação de As, Bi e Se. As proporções de analito:concomitante foram baseadas no universo das amostras usadas nesta dissertação para os elementos As e Se. Com esse estudo, pôde ser verificado que a seletividade foi grandemente afetada pela presença de Cu, Fe e Ni, para a determinação de As e Bi, no entanto, para a determinação de Se, os elementos Cu, Bi e As interferiram. Os testes de exatidão dos métodos propostos foram averiguados por meio do uso de materiais de referência certificados de amostras ambientais, bem como de interesse medicinal. Os valores encontrados foram concordantes com os valores certificados, segundo um intervalo de confiança de 95% de acordo com o teste t. Após o término do desenvolvimento de cada metodologia, os atomizadores foram cortados em diferentes pontos e foram obtidas algumas micrografias, bem como a composição da liga, por meio do detector de Raios-X. Com esse estudo foi possível inferir algumas explicações sobre a necessidade da injeção de um padrão concentrado no sistema para determinação de arsênio, bem como a descoberta de nanotubos de carbono na superfície do atomizador empregado na metodologia para determinação de bismuto. A existência de nanotubos de carbono foi confirmada por meio da técnica de TEM. Esse resultado é interessante, uma vez que o custo dos nanotubos é elevado e o mesmo tem sido empregado em diversas aplicações na Ciência. / Abstract: In this work, the metal atomizer (alloy INCONEL600®) efficiency in the HG-AAS technique was evaluated. It was divided into three Chapters, each one referring to the development of methodologies for arsenic, bismuth and selenium. Physical and chemical variables were evaluated using reference solutions of 50 mg L for As and Bi, and 400 mg L for Se. The evaluated variables were: acid, NaBH4 and NaOH concentration, length of the reaction coil, injected volume, carrier flow rate, argon carrier flow rate, inner diameter of the capillary, among others. The acid concentration for selenium determination was fixed at 7 mol L. After methodology optimization, some analytical parameters were obtained, respectively for As, Bi and Se: limit of detection - LOD, 2.3, 0.7 and 1.8 mg L, relative standard deviation - RSD, 5.8, 2.7 and 10% and regression coefficient - R, 0.9978, 0.9997 and 0.9974. The RSD of the method was based on As, Bi and Se analytical repeatability from samples. Then, a concomitant study was carried out for As, Bi and Se determination. The analyte:concomitant proportion for As and Se was based on those samples used in this work. This result showed that the presence of Cu, Fe and Ni greatly affected the selectivity for As and Bi, as well as Cu, Bi and As can be considered potential concomitants for Se. Certified reference materiais as well as medical samples were used for checking the accuracy of the proposed methods. By analyzing the results using the t test, no statistical difference at the 95% confidence level was found. After finishing the development of the analytical procedure as well as its application to real samples, each metal atomizer used for each developed methodology was then cut in different parts and morphological as well as X-ray analysis were performed to evaluate the metal distribution on the atomizer. From this study, some explanation was made about the necessity of the standard solution injection into the system for As determination. Additionally, carbon nanotubes were also found in the atomizer surfaces when it was applied to Si determination. Its presence was confirmed by the transmission electronic microscopy technique. / Mestrado / Quimica Analitica / Mestre em Química

This thesis is dealing with testing of two atomizers in combustion of liquid fuels and natural gas. There is a simple analysis of problems, principles and methods of atomizing liquids executed. Problem of pneumatic atomizing liquids is also described in detail. In the next chapters there is a plan and running of testing processed. Overall behavior of the atomizers and flame is evaluated from the outcome measurement and the power characteristics of atomizers and influence of GLR on the quality of combustion are determined. Overall rating of the testing is presented in conclusion this thesis.

No description available.

<div>In this experiment, swirl injectors were designed and tested to validate their use in spraying liquid </div><div>lead into a Barton pot combustion chamber to produce lead oxide at a smaller particle size than </div><div>the current stream injection. Testing was done with water and air to determine the best design for </div><div>atomization results, and then the injector was fabricated for liquid lead testing. Thermochemistry </div><div>calculations showed that due to lead oxidation being a surface reaction, the combustion process </div><div>was diffusion controlled. These conditions were used to determine residence time inside a Barton </div><div>pot combustion chamber for predicted droplet sizes. Results of the liquid lead testing showed that </div><div>final lead oxide particle size and residence time was reduced when using a swirl atomizer in place </div><div>of a steady feed stream. Further calculations were done to create a model for a standard combustion </div><div>chamber and injection system for lead oxide production.</div>