Call number: LD2668 .T4 1978 M42 / Master of Science

Thesis (MScEng)--University of Stellenbosch. / ENGLISH ABSTRACT: Aerosol synthesis involves the formation of condensable product species by gas-phase reaction, and the simultaneous growth of particles by coagulation. For the production of ceramic particles, reaction temperatures higher than 700 K are commonly used, and a maximum fusible particle size is observed. Coagulation-controlled growth yields spherical particles up to the maximum fusible size (approximately < 50 nm). Such particles coalesce rapidly and completely upon collision with other particles, whereas larger particles reach a meta-stable equilibrium for solid-state coalescence. Agglomerates with weak Van der Waal's bonds between particles inevitably form in the cooling/collection process. Coagulation of particles larger than the maximum fusible particle size yields agglomerates with significant neck growth between the primary particles. Spherical ceramic particles in the order of 1 J-Lm are favourable precursors for bulk electronic applications that require high purity. Such large spherical particles may possibly be produced in conditions of seed growth, which involves the deposition of small newly formed clusters onto larger existing particles. The central focus of the present work is to evaluate whether spherical ceramic particles significantly larger than the maximum fusible size may be produced by seed growth. The evaluation is done by modelling of process constraints and interpretation of published results. The modelling of constraints is based on a mathematical framework for comparison of different values of reactor design parameters. This framework comprises a simplified model system, a typology of quantities, and isolation of a set of independent design parameters. Comparison is done on the basis of fixed initial (seed) and final (product) particle sizes. The reactor design framework is used to evaluate the hypothesis on spherical seed growth, by assessing whether a reactor can be designed that satisfies all the process constraints. Future extension of the framework may allow optimisation for seed growth in general. The model system assumes laminar flow and isothermal conditions, and neglects the effect of reactor diameter on wall-deposition. The constraints are graphically represented in terms of the design parameters of initial reactant concentration and seed concentration. The effects of different temperatures and pressures on the constraints are also investigated. In a separate analysis, the suitability of turbulent flow for seed growth is assessed by calculating Brownian and turbulent collision coefficients for different colliding species. As turbulent intensity is increased, the seed coagulation rate is the first coagulation rate to be significantly enhanced by turbulence, resulting in a lowering of the maximum seed concentration allowed by the constraint for negligible seed coagulation. This tightening of a constraint by turbulence is the justification for considering only laminar flow for evaluating the hypothesis on spherical seed growth. Quantitative application of the model of constraints, as well as experimental and modelling results from the literature, did not demonstrate that significant spherical seed growth is possible without seed coagulation (agglomeration). As part of the conceptual effort in becoming familiar with aerosol reactor engineering, a simple two-mode plug-flow aerosol reactor model was developed, and verified with published results. This model has some novel value in that it translates the equations for aerosol dynamics into the terminology of reactor engineering. / AFRIKAANSE OPSOMMING: Aerosol sintese behels die gelyktydige chemiese vorming van 'n kondenseerbare spesie en die groei van partikels deur koagulasie. Temperature hoër as 700K word gewoonlik vir die aerosol sintese van keramieke gebruik. Partikels bo 'n sekere grootte kan nie saamsmelt nie. Koagulasie- beheerde groei lewer sferiese partikels tot en met die maksimum saamsmeltbare partikelgrootte (ongeveer < 50 nm). Wanneer sulke partikels bots, smelt hulle vinnig en volledig saam. Groter partikels bereik egter 'n meta-stabiele ewewig vir vastestof samesmelting. Agglomerate met swak Van der Waal's bindinge tussen partikels vorm onvermydelik wanneer die aerosol afgekoel word en die produk versamel word. Koagulasie van partikels groter as die maksimum saamsmeltbare grootte, lewer agglomerate met noemenswaardige nekvorming tussen primêre partikels. Sferiese keramiekpartikels in die ordegrootte van 1Mmis geskikte intermediêre produkte vir die vervaardiging van soliede eletroniese komponente waarvoor hoë materiaalsuiwerheid vereis word. Sulke groot sferiese partikels kan moontlik geproduseer word in toestande waar klein nuutgevormde partikels deponeer op groter bestaande partikels (saadpartikels). Die hoof-fokus van die huidige werk is om vas te stelof sferiese keramiekpartikels wat noemenswaardig groter is as die maksimum saamsmeltbare grootte, geproduseer kan word met die metode van saadpartikel-groei. Die moontlikheid word ondersoek deur 'n model van prosesbeperkings te maak, en deur gepubliseerde resultate te vertolk. Die model van prosesbeperkings is gegrond op 'n wiskundige raamwerk vir die vergelyking van verskillende waardes van reaktor ontwerp-parameters. Hierdie raamwerk bestaan uit 'n vereenvoudigde model-sisteem, 'n tipologie van verskillende soorte groothede, en die identifikasie van 'n stelonafhanklike ontwerp-parameters. Verskillende parameter-waardes word vergelyk vir dieselfde aanvanklike (saad) en resulterende (produk) partikelgroottes. Die reaktorontwerp-raamwerk word gebruik om die hipotese van sferiese saadpartikel-groei te evalueer, deur vas te stelof 'n reaktor ontwerp kan word wat aan al die prosesbeperkings voldoen. Mettertydse verfyning van die raamwerk kan dit moontlik geskik maak vir die optimering van saadpartikel-groei in die algemeen. Die model-sisteem is gebaseer op die aannames dat vloei laminêr en temperatuur konstant is, en die effek van reaktor-diameter op deponering op die reaktorwand word verontagsaam. Die posesbeperkings word grafies voorgestel in terme van oorspronklike reaktant-konsentrasie en saadpartikel-konsentrasie. Die effek van verskillende temperature en drukke op die prosesbeperkings word ook ondersoek. 'n Systaande ondersoek word gedoen oor die toepaslikheid van turbulente vloei vir saadpartikel- groei, deur botsings-koeffisiënte vir Brown-beweging en turbulensie te vergelyk. Wanneer turbulensie verhoog word, styg die koaguleringstempo van saadpartikels beduidend voordat ander koaguleringstempo's beduidend toeneem. Dit noodsaak 'n verlaging in die maksimum toelaatbare saadpartikel-konsentrasie om saadpartikel-koagulasie te verhoed. Hierdie verskerping van 'n prosesbeperking deur turbulente vloei, is die rede hoekom slegs laminêre vloei beskou word in die evaluering van die hipotese van sferiese saadpartikel-groei. Kwantitatiewe toepassing van die model van beperkings, asook eksperimentele en modellerings- resultate vanuit die literatuur, het nie getoon dat noemenswaardige groei van sferiese keramiekpartikels verkry kan word sonder saadpartikel-koagulasie (agglomerasie) nie. As deel van die proses om aerosol reaktor-ingenieurswese konsepsueelonder beheer te kry, is 'n eenvoudige twee-modus propvloei aerosol reaktor modelontwikkel. Die resultate van die model is bevestig deur vergelyking met gepubliseerde resultate. Hierdie model het die nuwigheid dat dit die vergelykings vir aerosol dinamika uitdruk in die terminologie van reaktor-ingenieurswese.

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The work presented in thesis is part of the DANIELA project which aims to replace the current air data system on civil aircrafts with a flush mounted Air Data System (ADS) built around a 3 axis Doppler LIDAR function as the primary data channel. This thesis is focused on the comparison of different window materials and their optical clarity by means of theoretical and experimental analysis. Four different window materials including BK7, Sapphire, Germanium and ZnS are placed in a wind tunnel. The samples are each exposed to flows of air and water for specific periods of time during which temperature, pressure and air speed are recorded. Subsequently, each sample is carefully observed under the microscope. This is followed by the measurement of the amount of back scatter via detecting the change in the voltage once it is placed in the optical station. The optical tests reveal the amount of dust adhered to the samples which results in increased voltage. Review of these samples under the microscope matches the results obtained from the optical test. The two sets of data obtained from the two tests determined that some samples collected more dust in comparison to others. It was established that under identical test conditions i.e. flow, temperature and moisture, BK7 and Sapphire collect considerably less dust compared to ZnS. Moreover it was impossible to test Germanium sample optically, under a microscope as it is a dark opaque glass.

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Approved for public release; distribution is unlimited / NOAA-7 AVHRR data from April 1982 and 1983 were used to perform a global scale analysis of aerosol particle characteristics. Several improvements were incorporated into an AVHRR multichannel satellite data technique developed by Pfeil (1986). This included better cloud and sunglint discrimination, removal of Rayleigh radiance and accounting for ozone absorption. The characteristics analyzed were optical depth and Aerosol Particle Size Index (S₁₂). S₁₂ provides the slope of the aerosol particle size distribution curve. Both of these parameters were evaluated during several naturally occurring events, foremost of which were the 1982 El Chicon eruption and the 1982-1983 El Nino-Southern Oscillation event. The results provided evidence that a significant amount of aerosol particles over marine regions are from land-derived sources. However, the results also provided evidence that some marine aerosol particles may be of biogenic origins, / http://archive.org/details/globalscaleestim00fros / Lieutenant, United States Navy

Orientador: Arnaldo Alves Cardoso / Banca: Mercedes de Moraes / Banca: Janaína Braga do Carmo / Banca: Lilian Rothschild Franco de Carvalho / Banca: Gisele Olimpio da Rocha / Resumo: Aerossóis são espécies sólidas ou líquidas suspendidas e/ou transportadas pelo ar, com diâmetro médio da ordem nano ou micrométrica. Os aerossóis podem modificar a atmosfera do planeta, afetar a saúde dos seres vivos, alterar a visibilidade e até mesmo o clima e a disponibilidade de água potável. Estes fatos justificam a necessidade de melhorar o conhecimento sobre suas características físicas e químicas. As rápidas mudanças na quantidade e composição dos aerossóis na atmosfera são resultados de atividades antrópicas que estão se intensificando como resultado de expansão econômica. Fora dos centros urbanos, as atividades relacionadas ao agronegócio são responsáveis por grande parte da emissão dos aerossóis. A região do centro-oeste paulista destaca-se pela grande área destinada à plantação de cana-de-açúcar. Parte significativa ainda utiliza a queima da palha para facilitação da colheita manual. O presente estudo descreve a caracterização química e física do material particulado atmosférico no interior do estado de São Paulo no período entre Maio de 2010 a Fevereiro de 2012. O maior número de amostras foi coletada na região central do estado, no município de Araraquara, dentro do Campus da Unesp, localizado a sudoeste da área urbana. Outras amostras foram coletadas a sudoeste do Estado, no município de Ourinhos, no Campus da UNESP, localizado a 5 km do centro urbano Nesta campanha participaram diferentes grupos de pesquisa. Para a coleta do aerossol utilizou-se filtros de Teflon e vazão de amostragem de ≈9 L min-1. Este procedimento possibilitou a coleta do material particulado suspenso total. Nas amostras coletadas foram determinadas as espécies iônicas solúveis em água por cromatografia de íons (NH4+, Na+, K+, Mg2+, Ca2+, Cl-, NO3-, SO42-, PO43-, C2O42-. O equipamento utilizado não permitiu a separação das espécies orgânicas acetato e formiato, apresentadas aqui como a somatórias... / Abstract: Aerosols are suspended solid or liquid species and / or airborne, with an average diameter of the nano or micron order. Aerosols can modify the atmosphere of the planet, affect the health of living beings, change the visibility and even the weather and availability of drinking water. These facts justify the need to improve the knowledge about their physical and chemical characteristics. Rapid changes in the amount and composition of aerosols in the atmosphere are the result of human activities, which are increasing as a result of economic expansion. Outside urban centers , the activities related to agribusiness are responsible for much of the emission of aerosols. The region of the center - west of São Paulo is distinguished by large area for sugar cane crop. Significant part still uses the of straw burning to facilitate the manual harvesting. The present study describes the chemical and physical characterization of atmospheric particulate matter in the state of São Paulo in the period from May 2010 to February 2012. The largest number of samples was collected in the central region of the state, the city of Araraquara, UNESP at the Campus, located southwest of the urban area. Other samples were collected southwest of the state , in the Ourinhos city, at the campus of UNESP, located 5 km from the city center. Together the campaign participated different research groups. To collect the aerosol was used Teflon filters and flow sampling ≈ 9 L min-1. This procedure allowed the collection of total suspended particulate matter. In the collected samples were determined water soluble ionic species by ion chromatography (NH4+, Na+, K+ , Mg2+ , Ca2+ , Cl- , NO3- , SO42- , PO43- , C2O42-). Equipment used did not enabled the separation of organic species acetate and formate, shown here as the summation of these organic anions ( H3CCOO- + HCOO-). In parallel directly measurements were performed to get the number concentration of particles... / Doutor

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by Mark Andrew Philip. / M.S.