Thesis (Ph.D.) - University of St Andrews, March 2009.

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.

Finite amplitude planetary waves are studied on a homogeneous fluid on both the rotating sphere and on a mid-latitude β-plane. The integrated equations of motion are rederived both on the rotating sphere, in a spherical polar co-ordinate system whose axis is tilted relative to the rotation axis, and on a mid-latitude β-plane. The linear solutions are re-examined and the errors associated with the non-divergent and the β-plane approximations are each shown to be about 10 to 15% for waves of a few thousand kilometers wavelength. Using the integrated equations of motion both on the sphere and on the β-plane, the linear non-divergent Rossby wave solutions are shown to be exact finite amplitude solutions. An exact topographic wave solution is also given for the case of an exponential depth profile. Such behaviour is not found for the divergent waves. Using a Stokes-type expansion in terms of an amplitude parameter, the second order solution for divergent Rossby waves is obtained, and it is found that, as in surface gravity wave theory, the first order correction to the phase velocity is zero. It is also shown that the linear non-divergent Rossby wave solution on a uniformly sheared zonal current is not a finite amplitude solution, and the second order solution is then calculated. Once again, the phase speed is correct to the first order. A class of long waves of permanent form analogous to the solitary and cnoidal waves of surface wave theory is obtained for a β-plane channel of either constant or exponentially varying depth. Such waves are found to exist in the divergent case in the absence of any zonal current; however, if the divergence is weak, or if the non-divergent approximation is made , then it is found, as it was by Larsen (1965), that these waves will exist only in the presence of a weakly sheared zonal current. On the exponential depth profile, such waves exist in the absence of a sheared zonal current, even if the non-divergent approximation is made. It is suggested that such waves may also exist trapped along long ocean ridges or scarps. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Application of conventional theory of transport and deposition to small particles or large colloids, on the order of 1 micron in diameter, has received surprisingly little attention in colloid science. While the favorable deposition of colloidal particles ( < 0.5 micron diameter) has repeatedly been shown to agree with the Smoluchowski-Levich approximation for a convective-diffusion process, larger particles are known to deviate from this solute-like mass transfer behavior. The rotating disk, used in the experiments performed in this work, is a model experimental system that has been employed in the past to de-convolute and quantify the mechanisms of particle transport. Experimental evidence shows that particle transport to the rotating disk deviates from the predictions of the complete three-dimensional convective-diffusion equation, including hydrodynamic and surface-surface interaction forces, in that non-uniform deposition is observed over the surface of the disk. Fluid inertial effects, observed to be significant in capillary flow, have been suggested in the literature as an explanation of non-uniform deposition on the rotating disk. Calculations performed in this work show that while inertial lift forces are significant, they are not the dominant cause of non-uniform deposition. Instead, hydrodynamic blocking of available deposition surface area is shown to accurately describe experimental deposition profiles. The effect of particle size on surface area exclusion and hydrodynamic scattering are separately assessed to demonstrate that the blocking model is not only phenomenologically accurate, but also an important part of the mechanistic description of transport in the rotating disk system.

No description available.

No description available.

No description available.

Master of Science / Department of Chemical Engineering / Larry E. Erickson / Caprolactam (C₆H₁₁NO) is produced in industry primarily as a monomer to be converted to nylon-6 via a polymerization reaction. More demanding purity requirements for nylon-6 have increased the performance requirements of extraction columns in the purification train of caprolactam production. Caprolactam is produced by performing a Beckmann Rearrangement on cyclohexanone oxime followed by a neutralization of the excess oleum post reaction. The resulting side product is ammonium sulfate in water with a residual amount of caprolactam that has to be extracted with benzene from the aqueous ammonium sulfate solution to reduce product losses. The aqueous caprolactam liquor is extracted in another column into benzene which purifies the product from water soluble impurities. The resulting caprolactam dissolved in benzene is back extracted into water where the final purification steps are completed prior to storage. Rotating disk contactor (RDC) extraction columns were invented by Royal Dutch Shell in the early 1950’s. The columns have a rotor in the center that is driven by an electric motor to rotate equally spaced flat disks inside the column. There are equally spaced annulus shaped stators that serve to provide mixing-separation compartments for each of the mounted disks on the rotor. Of the variables to consider for the optimum performance of the extraction in the RDC extraction column is the rotor speed. Rotor speed curves are generated for the 3 RDC extraction columns of the caprolactam purification as well as calculations of the number of theoretical stages for each of the columns based on actual performance data. Benzene is the solvent of choice in this purification process however recent push by environmental groups and agencies as well as tightening regulations have driven a desire to find a more benign alternative to benzene for this process. A review of the research and literature on potential alternative solvents for caprolactam purification is summarized with positives and drawbacks for each possible alternative.

Thesis. 1976. Ph.D.--Massachusetts Institute of Technology. Dept. of Mathematics. / Microfiche copy available in Archives and Science. / Bibliography: leaves 203-204. / Ph.D.

Resumo: O presente trabalho traz uma investigação experimental do escoamento em torno de um cilindro rotativo posicionado perpendicularmente à direção principal do escoamento, para números de Reynolds inferiores a 103. Os experimentos foram conduzidos em um túnel hidrodinâmico vertical, com seção de teste 146x146x500 mm e intensidade turbulenta da corrente livre inferior a 0,5%. O diâmetro do corpo de prova foi fixado em 6 mm, proporcionando um bloqueio sólido no interior da seção de testes pouco superior a 4%. A influência do número de Reynolds e da rotação específica do corpo de prova sobre a configuração do escoamento foi bastante estudada. A freqüência de emissão dos vórtices, necessária ao cálculo do número de Strouhal, foi determinada a partir da obtenção do sinal de velocidades, adquirido com o auxílio de um anemômetro de filme quente, ou através da técnica de contagem de fotogramas. Técnicas de visualização de escoamento foram, também, empregadas, em diferentes circunstâncias, tanto na análise qualitativa do escoamento, como para auxiliar o correto posicionamento das sondas de filme quente. Em vários ensaios, a visualização do escoamento por injeção de corante líquido a montante do corpo de prova foi utilizada, mostrando-se bastante eficiente, sobretudo no que concerne à qualidade das imagens obtidas. No entanto, esta técnica só possibilita a visualização de uma região bastante restrita do escoamento e, dependendo do posicionamento da agulha de injeção, diferentes configurações do escoamento podem ser observadas, dificultando a interpretação dos resultados. Para contornar esta situação, utilizou-se, também, a técnica de geração de bolhas de hidrogênio, que permite uma visão mais abrangente do campo de escoamento. De maneira geral, os resultados foram bastante satisfatórios quando comparados com a literatura, mostrando que a... (Resumo completo, clicar acesso eletrônico abaixo). / Abstract: This work presents an experimental investigation on the flow around a rotating cylinder positioned perpendicularly to the free stream, for Reynolds numbers up to 103. The experiments have been carried out inside a 146x146x500 mm test section of a vertical water tunnel, using a 6mm diameter cylinder, which has provided a lower than 4% blockage ratio inside the test section, under a less than 0.5% maximum free-stream turbulence intensity. The influence of both diameter-based Reynolds number and specific rotation of the cylinder on the flow configuration has been analyzed. The vortex shedding frequency, parameter necessary to evaluate the Strouhal number, has been determined from the velocity signal from hot film anemometer as well as directly through a framecounting technique. Two different methods of flow visualization, liquid dye and hydrogen bubble generation, has been also used under distinct circumstances, in order to provide a qualitative analysis of the flow, as well to obtain the correct location of the hot-film probes. In some experiments, flow patterns have been visualized by liquid dye injection upstream the test cylinder, propitiating a good image quality. Dye injection, however, allows for the visualization of a quite restricted area of the flow, in such a way that, depending on the needle location, several distinct flow configurations appear, making it very difficult the interpretation of the results. In order to mitigate those drawbacks, the technique of hydrogen bubble generation has also been employed, reaching for a far wider vision of the flow field. The achieved results have showed that the wake structure is strongly affected by the cylinder rotation, in such a way that the vortices generation can be totally inhibited for a values upper than 2, in the all range of the Reynolds number. / Orientador: Sérgio Said Mansur / Coorientador: Edson Del Rio Vieira / Banca: Marcos Pinotti Barbosa / Banca: André Luiz Seixlack / Mestre