[pt] A solução numérica de problemas de escoamentos de fluidos com transferência de calor, envolve a solução de um conjunto de equações diferenciais parciais não lineares acopladas. O maior esforço computacional gasto na solução dessas equações, é devido a solução dos sistemas algébricos resultantes da discretização das equações de conservação. A taxa de convergência de varios métodos iterativos é sensível a natureza do problema que está sendo resolvido. Portanto, nenhum método pode ser aclamado como melhor para todos os problemas. Junto com o desenvolvimento de novos métodos iterativos, o desenvolvimento de técnicas de aceleração da convergência dos métodos iterativos conhecidos é de consideravel interesse de ponto de vista prático. O objetivo primário do presente trabalho consistiu em analisar uma classe de algoritmos para a solução de sistemas algébricos provenientes da discretização das equações de conservação de fenômenos de transporte. O segundo objetivo foi o de selecionar um método adequado e eficiente que produza um aumento da taxa de convergência. Para este propósito, selecionou-se e implementou-se um esquema de - multigrid - por correção aditiva. Esta é uma técnica recente na qual o mesmo problema diferencial é aproximado em diversas malhas cujos tamanhos de malha são geralmente múltiplos integrais. Investigou-se seu desempenho para melhorar a taxa de convergência junto com o método iterativo linha por linha TDMA, e comparou-se seu desempenho com o método de correção por blocos. / [en] The numerical solution of fluid flows problems with heat transfer requires the solution of a set of coupled non- linear partial differencial equations. The major computational effort in solving these equations is due to the solution of the algebraic systems resultant from the discretization of the conservation equations. The convergence rate of iterative methods is sensitive to the nature of the problem being solved. Therefore, no one method may be claimed to be the best for all problems. Along with the development of new iterative methods, the development of technics for accelerating the convergence of known iterative methods presents a considerable interest from a practical standpoint. The primary objective of the present work was to analise a class of algorithms for the solution of algebraic systems resulting from the discretization of transport phenomena conservation equations. The second objective was to select an adequate and efficient method which lead an increase of the convergence rate. For this purpose a multigrid additive correction scheme was selected and implemented. This is a novel technique in which the same differential problem is approximated on several grids whose mesh sizes are usually integral multiples. It was investigated its performance to improve the convergence rate in combination with the iterative line-by-line TDMA as well as its performance with the use of block correction algorithm. / [es] La solución numérica de problemas de flujo de fluidos con transferencia de calor, comprende la solución de un conjunto de ecuaciones diferenciales parciales no lineales acopladas. El mayor esfuerzo computacional en la solución de esas ecuaciones, se debe a la resolución de los sistemas algebraicos resultantes de la discretización de las ecuaciones de conservación. La tasa de convergencia de varios métodos iterativos es altamente sensible a la naturaleza del problema. Por lo tanto, ningún método puede ser considerado como el

COSTA, Marcelo Henrique de Araújo Santos. Fenômenos de Transporte em Meios Porosos e Interfaces Fractais. 2006. 103 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2006. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-05-22T18:08:10Z No. of bitstreams: 1 2006_tese_mhascosta.pdf: 4361476 bytes, checksum: d1ad57b4bdfc1adb7ee1dc8cafc3333d (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-05-22T20:04:44Z (GMT) No. of bitstreams: 1 2006_tese_mhascosta.pdf: 4361476 bytes, checksum: d1ad57b4bdfc1adb7ee1dc8cafc3333d (MD5) / Made available in DSpace on 2015-05-22T20:04:44Z (GMT). No. of bitstreams: 1 2006_tese_mhascosta.pdf: 4361476 bytes, checksum: d1ad57b4bdfc1adb7ee1dc8cafc3333d (MD5) Previous issue date: 2006 / In this work, we investigate different transport phenomena through irregular media by means of numerical simulations. Initially, we study the effect of the critical percolation disorder on pore networks under diffusion-reaction conditions. Our results indicate the existence of three distinct regimes of reactivity, determined by the dimensionless parameter E=D/(Kl^2), where D is the molecular diffusivity of the reagent, K is its chemical reaction coefficient, and l is the length scale of the pore. At low values of E, the flux of the reacting species penetrating the network follows the classical scaling behavior, namely F~LE^(1/2). At intermediate values of E, the influence of the fractal morphology of the percolating cluster results in an anomalous behavior, F~L^(A/2)E^B, with an exponent B=0.34. At high values of E, the flux of the reagent reaches a saturation limit, F_SAT, that scales with the system size as F_SAT=L^A, with an exponent A=1.89, corresponding to the fractal dimension of the sample-spanning cluster. In the second part of this work, we study how the irregularity of the geometry influences the sequential deactivation of an interface accessed by diffusion. By using the notion of active zone, we propose a conjecture which constitutes an extension of Makarov theorem. In the third part, we investigate the steady-state heat transport in a fluid flowing through a two-dimensional channel whose walls are irregular interfaces. Once more, we apply the notion of active zone to investigate the effect of the interface geometry on the heat exchange efficiency of the system for different conductive-convective conditions. Compared with the behavior of a channel with smooth interfaces and under conditions in which the mechanism of heat conduction dominates, the results indicate that the effect of roughness is almost negligible on the efficiency of the heat transport system. On the other hand, when the convection becomes dominant, the role of the interface roughness is to generally increase both the heat flux across the wall as well as the active length of heat exchange, when compared with the smooth channel. Finally, we show that this last behavior is closely related with the presence of recirculation zones in the reentrant regions of the fractal geometry. / Neste trabalho investigamos diversos fenômenos de transporte tendo lugar através de meios irregulares por meio de simulação computacional. Inicialmente, tratamos do efeito da desordem crítica em redes percolantes de poros sujeitas à difusão e reação química. Verificamos a existência de três regimes distintos, determinados pelo parâmetro adimensional E=D/(Kl^2), onde D é a difusão molecular, K o coeficiente de reação química e l um comprimento característico. Para valores baixos de E, o fluxo de reagente que penetra a rede obedece à relação de escala clássica, F~LE^(1/2). Para valores intermediários de E, a influência da morfologia fractal do agregado de percolação resulta em um regime anômalo, F~L^(A/2)E^B, com um expoente B=0.34. Para valores altos de E, o fluxo de reagente atinge um limite de saturação, F_SAT, e escala com o tamanho do sistema na forma F_SAT=L^A, onde A=1.89 corresponde à dimensão fractal do agregado incipiente de percolação. Em uma segunda etapa do trabalho, analisamos o efeito da geometria irregular na desativação seqüencial de uma interface acessada por difusão. Aplicando o conceito de zona ativa, propomos uma conjectura que se constitui numa extensão do teorema de Makarov. Na terceira parte deste trabalho, investigamos o transporte estacionário de calor no escoamento de um fluido através de um tubo bidimensional, cujas paredes são interfaces irregulares. Mais uma vez, utilizando o conceito de zona ativa, investigamos o efeito da geometria da interface na eficiência de troca térmica do sistema em diferentes condições difusivo-convectivas. Em condições nas quais o mecanismo de transporte dominante é a condução, a comparação entre os resultados dos tubos liso e rugosos indica que o efeito da rugosidade é quase desprezível sobre a eficiência de dispositivos de transporte de calor. Por outro lado, quando a convecção torna-se dominante, a rugosidade passa a ter um papel importante e, em geral, o fluxo de calor e o comprimento da zona ativa aumentam com a rugosidade da interface de troca. Finalmente, mostramos que esse último comportamento está relacionado com as zonas de recirculação, presentes nas reentrâncias da geometria fractal.

O balanço populacional é um método comprovado de se aumentar a previsibilidade do comportamento de um sistema multifásico, e sua utilização em conjunto de técnicas de CFD tem sido cada vez maior pelo desenvolvimento constante de ambas as tecnologias. Este trabalho apresenta o equacionamento genérico do balanço populacional para sistemas bifásicos com agregação e quebra de partículas, além de uma discussão sobre a natureza de sistemas bifásicos. Métodos numéricos específicos para a resolução deste tipo de problema são discutidos, implementados e validados. Como exemplo de aplicação do equacionamento sugerido, é obtido um modelo específico para o caso de coalescência de gotas de água salgada dispersas numa fase óleo submetidas a um campo elétrico alternado, como no processo de dessalgação de petróleo. Um algoritmo baseado em autômatos celulares é utilizado como fonte de dados para validação do modelo e técnicas de CFD produzem um perfil de escoamento da emulsão. / The population balance is a proven method for increasing a multiphase systems behavior predictability, and its employment along with CFD techniques is increasing following the constant development of both technologies. This work presents the generic Population Balance Equations for two-phase systems where its particles suffer aggregation and breakage and a discussion on the nature of two-phase systems. Specific numerical methods for the solution of such problems are discussed, implemented and validated. A specific model for the coalescence of water droplets dispersed in an oily phase under the effects of an alternated electric field is obtained as an application example of the suggested equations, mimicking the oil desalting process. A cellular automata based algorithm is used as data source for the models validation and CFD techniques are used to produce the emulsions flow profile.

No description available.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22474号 / 工博第4735号 / 新制||工||1740(附属図書館) / 京都大学大学院工学研究科化学工学専攻 / (主査)教授 山本 量一, 教授 渡辺 宏, 准教授 谷口 貴志 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

The primary goal of this project is to develop an experimental setup for testing membrane materials. The membranes tested are all porous, hydrophilic and non- selective. The secondary goal is that the module finds use as an educational tool for learning about diffusion on a university level. The final setup consisted of two modified 250 ml polyethylene bottles with a wide neck joined together with a flange pinning the test object in between. In the experiments one side is loaded with a sodium chloride solution, while the other is loaded with pure deionized water. The conductivity change is then monitored in the chamber loaded with deionized water using a conductivity probe. Two test subjects are tested, an alpha Cellulose filter and a polycarbonate membrane. The mass transfer coefficient are determined to be 8.99*10-6 ± 3.90*10-6 [cm/min] and 3.62*10-5 ± 1.49*10-6 [cm/min] respectively. The large inconsistencies in the alpha cellulose filters results in large standard deviations, whereas the polycarbonate is very consistent and therefore have very small error bars. Meaning that the largest error in this design originates from inconsistencies between samples of the test subject. The setup is suitable as an educational tool due to short run times of one hour, the generated data only requires simple linear regression to extract mass transfer coefficients from the slope. The experiment can be varied further by adjusting temperature and stirring. / Det primära målet med det här projektet är att utveckla en experimentell uppställning för att testa membran. Alla testade membran är porösa, hydrofila och icke-selektiva. Det sekundära målet är att uppställningen kan användas som ett pedagogiskt verktyg för kurser i masstransport. Den slutliga uppställningen består av två modifierade 250 ml polyeten flaskor med vid hals, ihopsatta med en fläns som håller testobjektet på plats emellan flaskorna. I experimenten fylls en av kamrarna med saltlösning och den andra med avjoniserat vatten, konduktiviteten mäts i kammaren som laddas med avjoniserat vatten. Två objekt testades, ett alfacellulosa filter och ett polykarbonat membran. Massöverförings koefficienter bestämdes till 8.99*10-6 ± 3.90*10-6 [cm/min] för alfacellulosa filtret och 3.62*10-5 ± 1.49*10-6 [cm/min] för polykarbonat membranet. Det finns stora variationer i alfacellulosa materialet vilket leder till stora standardavvikelse i körningarna på alfacellulosa filtret, medan polykarbonat membranen var identiska och därmed har väldigt små felstaplar. Därmed kunde det fastslås att stora avvikelser nästan bara beror på variationer i testobjektet. Uppställningen lämpar sig för undervisning eftersom körningstiden är kort (1 timme) och massöverföringskoefficienten kan tas fram med linjär regression. Experimentet kan bland annat varieras genom att ändra temperatur och omrörning.

Multiphase transport phenomena primarily encompass the fundamental principles and applications concerning the systems where overall dynamics are precept by phase change evolution. On the other hand, multiscale transport phenomena essentially corroborate to a domain where the transport characteristics often contain components at disparate scales. Relevant examples as appropriate to multiphase and multiscale thermofluidic transport phenomena comprise solid-liquid phase change during conventional solidification process and hydrodynamics through narrow confinements. The additional effect of superimposed magnetic field over such multiphase and multiscale systems may give rise to intriguing transport characteristics, significantly unique in nature as compared to flows without it. The present investigation focuses on multiphase, multi-scale transport phenomena in physical systems subjected to the superimposed magnetic field, considering four important and inter-linked aspects. To begin with, for a multiphase system concerning binary alloy solidification, a normal mode linear stability analysis has been carried out to investigate stationary and oscillatory convective stability in the mushy layer in the presence of external magnetic field. The stability results indicate that the critical Rayleigh number for stationary convection shows a linear relationship with increasing Ham (mush Hartmann number). Magnetohydrodynamic effect imparts a stabilizing influence during stationary convection. In comparison to that of stationary convective mode, the oscillatory mode appears to be critically susceptible at higher values of  (a function of the Stefan number and concentration ratio), and vice versa for lower  values. Analogous to the behaviour for stationary convection, the magnetic field also offers a stabilizing effect in oscillatory convection and thus influences global stability of the mushy layer. Increasing magnetic strength shows reduction in the wavenumber and in the number of rolls formed in the mushy layer. In multiscale paradigm, the combined electroosmotic and pressure-driven transport through narrow confinements have been firstly analyzed with an effect of spatially varying non–uniform magnetic field. It has been found that a confluence of the steric interactions with the degree of wall charging (zeta potential) may result in heat transfer enhancement, and overall reduction in entropy generation of the system under appropriate conditions. In particular, it is revealed that a judicious selection of spatially varying magnetic field strength may lead to an augmentation in the heat transfer rate. It is also inferred that incorporating non–uniformity in distribution of the applied magnetic field translates the system to be dominated by the heat transfer irreversibility. Proceeding further, a semi-analytical investigation has been carried out considering implications of magnetohydrodynamic forces and interfacial slip on the heat transfer characteristics of streaming potential mediated flow in narrow fluidic confinements. An augmentation in the streaming potential field as attributable to the wall slip activated enhanced electromagnetohydrodynamic transport of the ionic species within the EDL has been found. Furthermore, the implications of Stern layer conductivity and magnetohydrodynamic influence on system irreversibility have been shown through analysis of entropy generation due to fluid friction and heat transfer. The results being obtained in this analysis have significant scientific and technological consequences in the context of novel design of future generation energy efficient devices, and can be useful in the further advancement of theory, simulation, and experimental work. Finally, the combined consequences of interfacial electrokinetics, rheology, and superimposed magnetic field subjected to a non-Newtonian (power-law obeying) fluid in a narrow confinement are studied in this work. The theoretical results demonstrate that the applied magnetic field imparts a retarding influence in the induced streaming potential development, whereas, triggers the heat transfer magnitude. Moreover, additional influences of power law index show reduction in heat transfer as well as the streaming potential magnitude. It is unveiled that the optimal combinations of power law index and the magnetic field lead to the minimization of the global total entropy generation in the system.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Zhongquan Zheng / A nano-material filter is an efficient device for improving indoor environmental quality (e.g. smoke reduction, air purification in buildings). Studying the effectiveness of nano-materials used in the device by computer simulation is challenging because very different size scales are involved. Therefore, numerical methods have to be developed to accommodate varying magnitudes of scales. In the current study, the simulation has been divided into three scales: macro-, micro- and nano-scale. The numerical schemes at each scale are targeted at a particular scale; however, the relationship of the general transport phenomena, physical mechanisms and properties among different scales are uniquely linked at the same time. The objective of the macro-scale simulation was to design and study a gas filter constructed with nano-material pellets. The filter was considered a packed-bed tube filled with manufactured nano-material pellets. Commercial computational fluid dynamics (CFD) packages were used along with the embedded programming macros. In the filtration process, we focused on the flow and species transport phenomena through the porous substrate. The mathematical/numerical models were built and tested based on the physical models used in the experimental setups for different materials that were tested. The results from the numerical models were validated and compared well to experimental data obtained from the pressure drop measurements and the adsorption (breakthrough) tests. In the micro-scale simulation, a modified immersed-boundary method (IBM) with the Zwikker-Kosten (ZK) porous model and the high-order schemes was validated and applied to simulate a representative porous unit that represented a periodic array of solid/porous cylinders. In the periodic unit, the solid cylinder case was used to validate the high-order schemes by comparing it to the results obtained from the commercial CFD software. The relationship between the pressure gradient and the porosity (Blake-Kozeny equation) was determined from this level and fed back to the macro-scale simulation, which provided a link between the two scales. In the porous cylinder case, both flow field and species transport were investigated with a porous model similar to the one used in the macro-scale. The species concentration change was calculated and found to be nonlinearly related to the adsorption coefficient. In the nano-scale simulation, a molecular dynamics (MD) simulation and a coupled molecular-continuum scheme were applied to solve the momentum and the mass transport problems at the molecular level at which the traditional continuum theory is no longer applicable. Both schemes were verified from the surface slip behavior study compared to the literature. The scale and shear effects in the Coutte flow were investigated, showing that in the micro-scale and macro-scale, the slip behavior could be neglected since it was only important in much smaller scales. The same hybrid scheme was then applied to a diffusion model with nano-pores constructed in the solid substrate. The adsorptions between various gases and the carbon substrate were simulated. The mass fluxes cross the fluid/solid interfaces were counted and both self-diffusivity and transport diffusivity were estimated and compared to their respective values found in the literature. The transport properties are closely related to the species transport (Fick’s law) in the macroscopic simulations. Linear concentration profiles in the channel were obtained based on those transport properties for various gases going through different sizes of nano-pores, which, as a connection to the continuum model, were to be used as boundary conditions in the continuum simulation.

In a 2D cell culture, the cells are mainly grown on flat surfaces which are usually made of polystyrene plastic. Cells are able to attach to these surfaces, forming individual cell formations or colonies. In this study, we have been looked at many different platforms to improve cell growth, adhesion, attachment and proliferation on two different promising cell lines. These cell lines are the human neural stem cells (hNSCs) and human liver hepatocellular carcinoma cells (HepG2). Researchers have been very interested in studying these cell lines in the recent years as they have very useful potentials in the long run to aid and cure many of the disorders, diseases and possibly replace infected or injured organs as well. This can be done using actual clinical applications for cell therapies and tissue transplantation. Based on the studies conducted for this thesis, we have been able to show that cells can be maintained in a 2D culture setting with increasing growth and adhesion factors. The conditions used for these studies were a way to not use the traditional materials for cell attachment and growth. This was pursued due to the fact that most stem cells for their continuity require a microenvironment that will support their physical and chemical properties of an effective extra cellular matrix (ECM). To reiterate, presently most ECM molecules are human or animal derived for effective cell culture applications but not clinical. This is a major problem as each batch varies, they are difficult to isolate and most contain biological components that have been known to limit their use in clinical applications. Hence, this study concentrated on developing synthetic polymer based ECMs as they do not have the problems of the human or animal derived ECMs, but also as they are relatively low-cost, reliable and easily fabricated. Through many experimental trials we have successfully developed synthetic polymer based ECM molecules that sustain stem cell growth for HepG2 liver hepatocellular carcinoma and hNSC human neural stem cell lines. The different substrates developed were a peptide fabricated in our lab; different concentrations and solutions of Poly 4-vinylphenol (P4VP) that were used on a flat hollow fiber membrane made using Polyacrylonitrile (PAN) doped in a solution containing PAN/N, N-dimethylformamide (DMF) having a high biocompatibility. This hollow fiber membrane study was maintained with eight different conditions over a period of 6 weeks.

A demanda do silício de grau solar (SiGS) utilizado na indústria fotovoltaica cresce atualmente em uma média de 35% ao ano e a projeção para a próxima década é de constante crescimento. Entretanto, a disponibilidade de matéria-prima para a produção do SiGS não tem crescido na mesma taxa, resultando em uma elevação de seu custo. Logo, a obtenção de rotas alternativas menos onerosas para a produção do SiGS torna-se crucial, principalmente sendo o Brasil o 3o maior produtor mundial de silício de grau metalúrgico. Tendo como objetivo a purificação do silício, o presente trabalho de pesquisa apresenta um estudo detalhado da solidificação direcional do silício, que é uma das etapas utilizadas em todas as rotas alternativas atualmente pesquisadas com o objetivo de purificação. Este estudo foi realizado em um forno do tipo Bridgman vertical, onde o silício líquido contido em um molde foi extraído da região quente do forno, resultando em uma solidificação direcional controlada e ascendente. Dois tipos de silício foram escolhidos como material de entrada para o processo de refino: o silício de grau metalúrgico e o silício de grau metalúrgico pré-refinado por lixiviação. Quatro velocidades de extração do molde entre 5 a 110 mm/s foram empregadas nos ensaios. A macrossegregação de impurezas nos lingotes obtidos foi medida através de análises químicas e a estrutura metalúrgica observada através de macro e micrografias. Os lingotes solidificados com menor velocidade de extração, onde se observa evidências de uma interface sólido-líquido plana, apresentam um grau de refino superior aos de maior velocidade, que mostram evidências de uma interface celular ou dendrítica. As análises químicas mostram que, após a solidificação direcional, os teores de Fe, Al, Cr e Ti medidos nas regiões da base e central dos lingotes atingem níveis especificados para o SiGS por alguns autores. / The demand for solar grade silicon (SiGS) in the photovoltaic industry has grown 35% per year and a constant growth rate is predicted for the next decade. The availability of feedstock to produce SiGS, however, has not grown at the same rate, resulting in increasing SiGS cost. Consequently, the development of less expensive alternative processing routes is of paramount importance to the photovoltaic industry in general, and particularly to Brazil, which is the 3rd largest producer of metallurgical grade silicon. The objective of the present work is to study the directional solidification of silicon, which is a step adopted in virtually all alternative processing routes under development to refine silicon. The directional solidification of silicon was carried out in a vertical Bridgman furnace, where liquid silicon was poured into a quartz mold, which was extracted at constant velocity from the hot region of the furnace, resulting in ascending directional solidification. Two types of feedstock silicon were used, namely, a metallurgical grade silicon that was refined by leaching prior to directional solidification and metallurgical grade silicon as-received from the manufacturer. The quartz molds with liquid silicon were extracted at four different velocities in the range from 5 to 110 mm/s. In the solidified silicon ingots, the macrosegregation of elements were measured using accurate analytical techniques, whereas the metallurgical structures were observed in macro and micrographs. The ingots solidified at lower extraction velocities, at which evidences of a planar solidliquid interface were observed, showed greater refining effect than those solidified at larger velocities, which showed evidences of a cellular or dendritic solid-liquid interface. The contents of Fe, Al, Cr, and Ti measured at the base and center portions of the solidified ingots comply with the specifications of SiGS proposed by some authors.