Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Alfred Walters Reed. / Ph.D.

Thesis (Nav. Arch.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering; and, (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1975. / Bibliography: leaves 248-249. / M.S. / Nav. Arch.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 182-188. / by Juan J. Manzano-Ruiz. / Ph.D.

<div>Incompressible single-phase and two-phase flows are widely encountered in and underlie many engineering applications. In this thesis, we aim to develop efficient methods and algorithms for numerical simulations of these classes of problems. Specically, we present two schemes: (1) a modied consistent splitting scheme for incompressible single-phase flows with open/out flow boundaries; (2) a three-dimensional hybrid spectral element-Fourier spectral method for wall-bounded two-phase flows.</div><div><br></div><div><div>In the first part of this thesis, we present a modied consistent splitting type scheme together with a family of energy stable outflow boundary conditions for incompressible single-phase outflow simulations. The key distinction of this scheme lies</div><div>in the algorithmic reformulation of the viscous term, which enables the simulation of outflow problems on severely-truncated domains at moderate to high Reynolds numbers. In contrast, the standard consistent splitting scheme is observed to exhibit a numerical instability even at relatively low Reynolds numbers, and this numerical instability is in addition to the backflow instability commonly known to be associated with strong vortices or backflows at the outflow boundary. Extensive numerical experiments are presented for a range of Reynolds numbers to demonstrate the effectiveness and accuracy of the proposed algorithm for this class of flows.</div></div><div><br></div><div><div>In the second part of this thesis, we present a numerical algorithm within the phase-field framework for simulating three-dimensional (3D) incompressible two-phase flows in flow domains with one homogeneous direction. In this numerical method, we represent the flow variables using Fourier spectral expansions along the homogeneous direction and C0 spectral element expansions in the other directions. This is followed by using fast Fourier transforms so that the solution to the 3D problem is obtained by solving a set of decoupled equations about the Fourier modes for each flow variable. The computations for solving these decoupled equations are performed in parallel to effciently simulate the 3D two-phase</div><div>ows. Extensive numerical experiments are presented to demonstrate the performance and the capabilities of the scheme in simulating this class of flows.</div></div>

Modélisation des transferts de masse et de chaleur dans une cellule d'électrolyse de production de fluor. La production de fluor par électrolyse est une étape clé de la conversion de l’uranium dans l’industrie nucléaire. Afin d’optimiser ce procédé, les travaux de thèse décrits dans ce manuscrit se sont concentrés sur deux axes : le développement d’un modèle numérique de l’électrolyseur et l’étude du phénomène d’hyperpolarisation cathodique néfaste pour le bon fonctionnement de la cellule. Un modèle couplant plusieurs physiques (thermique avec solidification, diphasique, électrocinétique) a été développé et des essais expérimentaux ont été menés afin d’acquérir, d’une part, certaines propriétés physiques de l’électrolyte nécessaires aux simulations (conductivité thermique et capacité thermique à pression constante) et, d’autre part, des données expérimentales permettant de qualifier le modèle obtenu. Ce travail de modélisation a abouti à l’obtention d’un modèle 3D fiable couplant les physiques citées précédemment, ceci à l’échelle d’un pilote R&D semi-industriel. L’impact de la solidification de l’électrolyte sur le transfert de chaleur a également pu être simulé pour la première fois. Ces essais ont également permis de fournir des premières explications sur le phénomène d’hyperpolarisation cathodique en dressant des tendances claires quant à l’influence de certains paramètres de contrôle de l’électrolyseur comme le titre HF et la température de consigne. / Computer modeling of heat transfer and mass transfer in an electrolytic cell for production of fluorineElectrolytic production of fluorine is a key step in uranium conversion for the nuclear industry. In order to improve this process, the work described in this dissertation aims at two main objectives: to build a numerical simulation of the electrolysis cell and to understand the cathodic hyperpolarization effect which lowers the productivity of the cell. A model coupling several physics (heat transfer with solidification, two-phase flow, electrokinetics) has been developed and experiments were made in order to evaluate unknown physical properties of the electrolyte (thermal conductivity and heat capacity at constant pressure). Experimental data were also acquired in order to assess the capacity of the model to simulate various phenomena occurring inside the cell. Eventually, a reliable 3D model of a semi-industrial R&D cell coupling the physics above mentioned has been obtained. The negative impact of the solidification of the electrolyte on the cooling system was simulated for the first time. Thanks to these experiments, it was also possible to determine the major trends which drive the cathodic hyperpolarization effect. The influence of HF mass fraction and temperature on this phenomenon was clearly shown.

Em linhas gerais, esta dissertação de mestrado envolve o estudo de padrões de escoaomento durante a ebulição convectiva em microcanais. Resultados experimentais foram levantados para um tubo com diâmetro de 2,32 mm durante a evaporação convectiva dos refrigerantes R134a e R245fa. Para a investigação, técnicas experimentais e de análise foram desenvolvidas. A caracterização dos padrões de escoamento envolveu o tratamento simultâneo de sinais provenientes dos seguintes dispositivos: um par diodo/sensor-laser tendo um tubo transparente entre eles no interior do qual ocorre o escoamento bifásico; um transdutor de pressão piezo-elétrico de tamanho reduzido com o objetivo de determinar a variação local da pressão do escoamento; e de um micro-termopar em contato com o fluido refrigerante. A técnica de tratamento de dados utilizada envolve a aglomeração progressiva de dados que apresentem características médias similares através do algoritmo k-means. Os sinais de pressão, intensidade de radiação e temperatura foram adquiridos simultaneamente a uma freqüência de 25 kHz. Imagens simultâneas do escoamento bifásico a uma velocidade de captura em torno de 10.000 imagens/s foram levantadas através de uma câmera de filmagem rápida (até 100.000 imagens/s), e os padrões de escoamentos observados contrastados aos resultados fornecidos pelo método proposto. Baseado nesta análise, mapas de escoamento foram propostos, os quais incorporaram não apenas critérios subjetivos como a visualização, mas também objetivos como as variações transientes da pressão local do escoamento e da morfologia do escoamento através do seu efeito na dispersão da radiação emitida pelo foto-diodo. Os resultados previstos pelo método objetivo apresentam concordância razoável com os dados caracterizados com base em visualizações. Adicionalmente, características de bolhas alongadas foram determinadas. / The present research has been focused on the study of flow patterns inside channels of diameter less than 3 mm during the convective evaporation of refrigerants such as R134a and R245fa. For the investigation of such topics, experimental techniques and methods of analysis of results were developed. A broad database was gathered in an experimental test facility. The characterization of flow patterns involved the simultaneous processing of signals from the following devices: a pair diode / laser-sensor having a transparent tube between them, within which occurs the two-phase flow; a micro piezoelectric pressure transducer to determine the local variation of pressure of the flow and a micro-thermocouple fixed within the fluid. The technique used in data processing involves the gradual agglomeration of data having similar average characteristics; this method was developed based on the k-means clustering algorithm. The signals from the transducers were acquired simultaneously at a frequency of 25 kHz. The program for the acquisition and for processing of the signals was developed using LabView. Simultaneous images of two-phase flow at a speed of capture around 10,000 images / s were obtained through a high speed camera and the observed flow patterns were contrasted to the results provided by the objective method. Based on this analysis, flow maps were proposed, which incorporate not only subjective criteria such as visualization, but also objective criteria like the transient variations of local pressure of the flow, temperature of the fluid and the effect of the flow morphology based on the dispersion of light which effect was captured by the photo-diode. The maps obtained by the objective method were compared against flow pattern segregated based on visualization and a reasonable agreement was obtained. Besides the elongated bubble characteristics were determined.

Two-phase flow, ubiquitous to waterflood oil recovery, geological CO2 storage, and groundwater remediation, is strongly influenced by wettability, and made more complex under mixed-wet conditions. Optimum wettability for such operations is not well established due to limited experimental data and difficulties in their interpretation. This thesis investigates the impact of mixed-wettability, characterised by advancing contact angle θa on capillary pressure, relative permeability, and waterflood displacement. Using a Darcy scale simulator, relative permeability kr, capillary pressure Pc, and residual oil saturation Sor were extracted by history matching production and pressure drop data from centrifuge brine invasion and waterflood displacements completed for a range of θa. As θa increased, a larger |Pc| was required to displace oil from mixed-wet cores at high initial oil saturation. End point oil and brine permeability decreased with increasing θa. A permeability enhancement, such that kr > 1, was measured both when the flowing phase was wetting and non-wetting and was attributed to a slippage at the oil/brine interface directly correlated to θa. Residual oil saturation decreased monotonically with increasing θa while core-averaged remaining oil saturation at the end of the waterflood exhibited a non-monotonic dependence on θa. Simulations of the waterfloods revealed that both significant capillary end effects and premature termination of the waterflood in the laboratory contribute to the deviation between remaining and residual saturations. This work demonstrates that the former is not representative of the latter, as it has been assumed in a number of studies in the literature. Both corefloods and microfluidic waterfloods show the importance of combining experimental studies with simulation for correct interpretation of the measurements especially under capillary dominated flow.

A distribuição do tamanho de bolhas é uma importante característica em sistemas bifásicos. A área interfacial de bolhas está fortemente relacionada às taxas de reações químicas e de transferência de massa em aplicações industriais como colunas de destilação e fermentação, sistemas biológicos, oxidação, hidrogenação, tratamento de água, e em processos naturais, como dinâmicas de aerossóis e transferência de gás oceano-atmosfera. Pontas de provas intrusivas são largamente usadas para determinar a distribuição do tamanho de bolhas em colunas de borbulhamento bifásicas. Embora o tamanho de bolhas não possa ser obtido diretamente pelo uso de uma simples ponta de prova porque estas medem somente comprimentos perfurados em bolhas, é possível relacionar distribuições de cordas à distribuição de tamanho de bolhas usando análises estatísticas. Este trabalho apresenta a implementação de um sistema capaz de medir distribuição de tamanho de bolhas em uma coluna de borbulhamento composta por água e ar através de uma ponta de prova condutiva. Imagens obtidas por uma câmera de vídeo CCD (Charge-Coupled Devices) monocromática são usadas para validar e calibrar o sistema. / The distribution of bubble sizes is a critical feature in two–phase systems. The interfacial area of bubbles is strongly related to chemical reaction and mass transfer rates in industrial applications such as distillation and fermentation columns, biological systems, oxidation, hydrogenation, waste water treatment and in natural processes such as aerosol dynamics and air-sea gas transfer. Intrusive probes are widely used to determine bubble size distribution in two-phase bubble columns. Although bubble size cannot be obtained by a simple probe because it measures only the pierced length of the bubbles, it is possible to relate chord distributions to bubble size distribution by the use of statistical analysis. This work proposes a system implementation which is able to determine bubble size distribution in a water-air bubble column using an intrusive conductance probe. Images obtained by a monochromatic video camera CCD (Charge-Coupled Devices) are used to validate and calibrate the system.

Bromelina é um nome coletivo para enzimas proteolíticas encontradas no talo, fruto e folhas do abacaxi (Ananas comosus Merr). A bromelina possui propriedades anti-inflamatórias, de debridamento, entre outras. Para a produção da bromelina deve-se, preferencialmente, usar resíduos do abacaxi, visto que os produtos do fruto têm aplicação comercial. Este trabalho teve como objetivo a extração de bromelina a partir de cascas de abacaxi através de sistema de duas fases aquosas (SDFA), e sua aplicação em hidrogel polimérico. Foram realizados estudos de estabilidade da bromelina comercial, em que se observou maior estabilidade em pH 5,0 com menor perda da atividade relativa em todas as temperaturas estudadas (20, 30, 40 e 50°C). O estudo da extração da bromelina em SDFA formado por polietileno glicol (PEG) e ácido poliacrílico (PAA) (com auxílio da análise de variância de parâmetros como rendimento, fator de purificação e coeficiente de partição) proporcionou rendimento de 335% e fator de purificação de 25,8. Os hidrogéis poliméricos à base de PEG estudados apresentaram-se flexíveis, com pouca elasticidade e taxa de absorção superior a 1000%. Hidrogel carreado de bromelina pelo método de turgescência proporcionou a maior liberação da enzima, assim como a maior atividade (80% da bromelina liberada em 24 h e 278 ± 89 U/mL). / Bromelain is a collective name for the proteolytic enzymes found in the stem, fruit and leaves of pineapple (Ananas comosus Merr.). Bromelain possesses anti-inflammatory properties, debridement, among others. For bromelain production one should preferably use the waste materials, whereas pineapple fruit products have commercial application. This study aimed to extract bromelain from pineapple peels using aqueous two-phase system (ATPS), and its application in polymeric hydrogels. Stability studies of commercial bromelain were performed, which found greater stability at pH 5.0 with minor loss of relative activity at all temperatures studied. The study of bromelain extraction in ATPS composed by polyethylene glycol (PEG) and poly acrylic acid (PAA) (with assistance of variance analysis of parameters such as yield, purification factor and partition coefficient) showed yield 335% and purification factor of 25.8. The PEG-based hydrogels studied presented flexibility, low elasticity and swelling ratio higher than 1000%. Hydrogel containing bromelain, loading by embedding (solvent sorption) method, yielded the highest enzyme release, as well as the highest activity (80% bromelain released over 24 h and 278 ± 89 U / mL).

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Mohamed Tayeb Benchaita. / Ph.D.