Investigation expérimentale des contraintes hémodynamiques d'un fantôme d'artère sténosée

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Investigation expérimentale des contraintes hémodynamiques d'un fantôme d'artère sténosée

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Leanin soveltaminen haavanhoitotuotteiden valmistuksen läpimenoaikojen lyhentämiseksi

Mölnlycke Health Care valmistaa kertakäyttöisiä leikkaussali- ja haavanhoitotuotteita. Yritys on saavuttanut arvostetun aseman markkinoilla ja pitääkseen asemansa sen tulee koko ajan kehittää toimintaansa. Keväällä 2016 yritys aloitti leanin implementoinnin, minkä vuoksi nykytilanteen kartoittaminen ja sen pohjalta tuotannon kehittäminen tuli ajankohtaiseksi. Diplomityössä selvitettiin Mölnlycke Health Care Oy:lle sopiva nykytilan kartoitusmenetelmä. Sopivaksi menetelmäksi osoittautui arvovirtakuvaus. Nykytilanteen kartoitus tehtiin yrityksen kannalta tärkeälle tuoteperheelle, joka tässä tapauksessa oli edistyksellinen haavanhoitotuote ja haavasidos Mepilex Border. Nykytilanteen kartoitus antoi tuotteen läpimenoajaksi 100 päivää varaston riitto huomioituna. Tästä ajasta kuitenkin suurin osa oli hukkaa, jota pystytään poistamaan. Nykytilanteesta tehtiin kuva, jonka pohjalta pystyttiin havainnoimaan kehittävät kohteet ja tekemään ehdotukset kohteiden parantamiseksi. Kehitysehdotusten tavoitteena oli tuoda yritystä lähemmäs Lean-filosofiaa ja auttaa pitämään yllä jatkuvan parantamisen kulttuuria.

Muuttuva lapsen maailma. Minttu-kuvakirjat viidellä vuosikymmenellä 1978–2015.

Tutkimuksen tavoitteena on selvittää, miten kuvaa lapsuudesta rakennetaan verbaalisilla ja visuaalisilla elementeillä kuvakirjan tarjoamien mahdollisuuksien ja rajoitusten puitteissa. Tutkimuskohteinani toimivat Maikki Harjanteen Minttu-kuvakirjoista löytämäni kirjaparit. Samasta aiheesta kirjoitettuja kirjapareja ovat joulusta kertovat kirjat mintun joulu (1979) ja Mintun joulukirja (1989), lemmikin liittymistä Mintun perheeseen käsittelevät kirjat minttu saa koiran (1982) ja Minttu saa oman koiran (2007), mummon nimikkoteokset minttu mummolassa (1978) ja Minttu ja mummo (2010) sekä syntymäpäivistä kertovat kirjat mintun kiva päivä (1979) ja Mintun syntymäpäivät (2014). Tutkin siis, miten kuvaa lemmikeistä, koirista, mummoista, jouluista ja syntymäpäivistä rakennetaan näissä kuvakirjapareissa. Tutkin tutkimuskohteitani ikonoteksteinä eli teoksina, jotka muodostuvat sanan ja kuvan vuorovaikutuksessa. Kuvan ja sanan suhteessa tapahtuneen muutoksen määrittelyn apuna käytän Ulla Rhedinin kolmea kuvakirjakategoriaa sekä Maria Nikolajevan ja Carole Scottin kertovuuden aspektin varaan perustuvaa kuvakirjajaottelua. Representaation ymmärrän Mikko Lehtosen ja Stuart Hallin tapaan kaksisuuntaiseksi ilmiöksi, toisinnoksi, jolla on kuitenkin maailmaa muokkaava voima. Mintut ovat muuttuneet 70-luvun ensimmäisistä kuvakirjoista 2010-luvulle paljon niin visuaalisesti kuin verbaalisesti, mikä on vaikuttanut kirjojen tuottamaan lemmikki-, mummo-, joulu- ja syntymäpäiväkuvaan. Alkutuotannossa painottui kerronnan visuaalinen puoli ja lopputuotannossa tekstin osuus kerronnassa on kasvanut suureksi. Alkutuotannon Mintut pyrkivät mimeettiseen ja realistiseen kuvaukseen kun taas lopputuotanto saa karnevalismin ja nonsensen piirteitä. Samalla Minttujen arvot ovat säilyneet jokseenkin samoina: Vaikka Minttu-kirjoissa representoidaankin melko idyllisesti boheemia lapsiperheen arkea, löytyy niistä säröjä, joilla Mintut kyseenalaistavat valtakulttuuria. Mintut puhuvat vihreiden arvojen puolesta kulutuskulttuuria vastaan ja tekevät selväksi, ettei lapsi tarvitse leluja ja kalliita harrastuksia, vaan oman tärkeän aikuisen aikaa. Minttu-kuvakirjat tuottavat tietynlaista kuvaa lapsuudesta eri vuosikymmenillä. Kuvakirjat luovat omaa todellisuuttaan representoidessaan asioita, eikä niitä voida pitää vallan käytön suhteen neutraalina mediana. Niillä on agenda muuttaa maailmaa.

Investigation expérimentale du décollement dans l’aspirateur d’une turbine bulbe

La présente thèse propose une étude expérimentale du décollement dans le diffuseur d’un modèle de turbine hydroélectrique bulbe. Le décollement se produit quand la turbine est opérée à forte charge et il réduit la section effective de récupération du diffuseur. La diminution de la performance du diffuseur à forte charge engendre une baisse brusque de l’efficacité de la turbine et de la puissance extraite. Le modèle réduit de bulbe est fidèle aux machines modernes avec un diffuseur particulièrement divergent. Les performances de la turbine sont mesurées sur une large gamme de points d’opération pour déterminer les conditions les plus intéressantes pour l’étude du décollement et pour étudier la distribution paramétrique de ce phénomène. La pression est mesurée le long de l’aspirateur par des capteurs dynamiques affleurants alors que les champs de vitesse dans la zone de décollement sont mesurés avec une méthode PIV à deux composantes. Les observations à la paroi sont pour leur part faites à l’aide de brins de laine. Pour un débit suffisant, le gradient de pression adverse induit par la géométrie du diffuseur affaiblit suffisamment la couche limite, entraînant ainsi l’éjection de fluide de la paroi le long d’une large enveloppe tridimensionelle. Le décollement instationnaire tridimensionnel se situe dans la même zone du diffuseur indépendamment du point d’opération. L’augmentation du débit provoque à la fois une extension de la zone de décollement et une augmentation de l’occurrence de ses manifestations. La position et la forme du front de décollement fluctue significativement sans périodicité. L’analyse topologique et celle des tourbillons des champs de vitesse instantanés montrent une topologie du front de décollement complexe qui diffère beaucoup d’une réalisation à l’autre. Bien que l’écoulement soit turbulent, les tourbillons associés aux foyers du front sont clairement plus gros et plus intenses que ceux de la turbulence. Cela suggère que le mécanisme d’enroulement menant aux tourbillons du décollement est clairement distinct des mécanismes de la turbulence.

Studies of turbulent flows in continuous casting of steel with and without magnetic field

This thesis develops and tests various transient and steady-state computational models such as direct numerical simulation (DNS), large eddy simulation (LES), filtered unsteady Reynolds-averaged Navier-Stokes (URANS) and steady Reynolds-averaged Navier-Stokes (RANS) with and without magnetic field to investigate turbulent flows in canonical as well as in the nozzle and mold geometries of the continuous casting process. The direct numerical simulations are first performed in channel, square and 2:1 aspect rectangular ducts to investigate the effect of magnetic field on turbulent flows. The rectangular duct is a more practical geometry for continuous casting nozzle and mold and has the option of applying magnetic field either perpendicular to broader side or shorter side. This work forms the part of a graphic processing unit (GPU) based CFD code (CU-FLOW) development for magnetohydrodynamic (MHD) turbulent flows. The DNS results revealed interesting effects of the magnetic field and its orientation on primary, secondary flows (instantaneous and mean), Reynolds stresses, turbulent kinetic energy (TKE) budgets, momentum budgets and frictional losses, besides providing DNS database for two-wall bounded square and rectangular duct MHD turbulent flows. Further, the low- and high-Reynolds number RANS models (k-ε and Reynolds stress models) are developed and tested with DNS databases for channel and square duct flows with and without magnetic field. The MHD sink terms in k- and ε-equations are implemented as proposed by Kenjereš and Hanjalić using a user defined function (UDF) in FLUENT. This work revealed varying accuracies of different RANS models at different levels. This work is useful for industry to understand the accuracies of these models, including continuous casting. After realizing the accuracy and computational cost of RANS models, the steady-state k-ε model is then combined with the particle image velocimetry (PIV) and impeller probe velocity measurements in a 1/3rd scale water model to study the flow quality coming out of the well- and mountain-bottom nozzles and the effect of stopper-rod misalignment on fluid flow. The mountain-bottom nozzle was found more prone to the longtime asymmetries and higher surface velocities. The left misalignment of stopper gave higher surface velocity on the right leading to significantly large number of vortices forming behind the nozzle on the left. Later, the transient and steady-state models such as LES, filtered URANS and steady RANS models are combined with ultrasonic Doppler velocimetry (UDV) measurements in a GaInSn model of typical continuous casting process. LES-CU-LOW is the fastest and the most accurate model owing to much finer mesh and a smaller timestep. This work provided a good understanding on the performance of these models. The behavior of instantaneous flows, Reynolds stresses and proper orthogonal decomposition (POD) analysis quantified the nozzle bottom swirl and its importance on the turbulent flow in the mold. Afterwards, the aforementioned work in GaInSn model is extended with electromagnetic braking (EMBr) to help optimize a ruler-type brake and its location for the continuous casting process. The magnetic field suppressed turbulence and promoted vortical structures with their axis aligned with the magnetic field suggesting tendency towards 2-d turbulence. The stronger magnetic field at the nozzle well and around the jet region created large scale and lower frequency flow behavior by suppressing nozzle bottom swirl and its front-back alternation. Based on this work, it is advised to avoid stronger magnetic field around jet and nozzle bottom to get more stable and less defect prone flow.

Surface acoustic wave streaming in a PDMS microfluidic system: effect of frequency and fluid geometry & A remote ultrasonic glucose sensor

This thesis describes two separate projects. The first is a theoretical and experimental investigation of surface acoustic wave streaming in microfluidics. The second is the development of a novel acoustic glucose sensor. A separate abstract is given for each here. Optimization of acoustic streaming in microfluidic channels by SAWs Surface Acoustic Waves, (SAWs) actuated on flat piezoelectric substrates constitute a convenient and versatile tool for microfluidic manipulation due to the easy and versatile interfacing with microfluidic droplets and channels. The acoustic streaming effect can be exploited to drive fast streaming and pumping of fluids in microchannels and droplets (Shilton et al. 2014; Schmid et al. 2011), as well as size dependant sorting of particles in centrifugal flows and vortices (Franke et al. 2009; Rogers et al. 2010). Although the theory describing acoustic streaming by SAWs is well understood, very little attention has been paid to the optimisation of SAW streaming by the correct selection of frequency. In this thesis a finite element simulation of the fluid streaming in a microfluidic chamber due to a SAW beam was constructed and verified against micro-PIV measurements of the fluid flow in a fabricated device. It was found that there is an optimum frequency that generates the fastest streaming dependent on the height and width of the chamber. It is hoped this will serve as a design tool for those who want to optimally match SAW frequency with a particular microfluidic design. An acoustic glucose sensor Diabetes mellitus is a disease characterised by an inability to properly regulate blood glucose levels. In order to keep glucose levels under control some diabetics require regular injections of insulin. Continuous monitoring of glucose has been demonstrated to improve the management of diabetes (Zick et al. 2007; Heinemann & DeVries 2014), however there is a low patient uptake of continuous glucose monitoring systems due to the invasive nature of the current technology (Ramchandani et al. 2011). In this thesis a novel way of monitoring glucose levels is proposed which would use ultrasonic waves to ‘read’ a subcutaneous glucose sensitive-implant, which is only minimally invasive. The implant is an acoustic analogy of a Bragg stack with a ‘defect’ layer that acts as the sensing layer. A numerical study was performed on how the physical changes in the sensing layer can be deduced by monitoring the reflection amplitude spectrum of ultrasonic waves reflected from the implant. Coupled modes between the skin and the sensing layer were found to be a potential source of error and drift in the measurement. It was found that by increasing the number of layers in the stack that this could be minimized. A laboratory proof of concept system was developed using a glucose sensitive hydrogel as the sensing layer. It was possible to monitor the changing thickness and speed of sound of the hydrogel due to physiological relevant changes in glucose concentration.

Air Entrainment in the Turbulent Ship Hull Boundary Layer

Turbulent fluctuations in the vicinity of the water free surface along a flat, vertically oriented surface-piercing plate are studied experimentally using a laboratory-scale experiment. In this experiment, a meter-wide stainless steel belt travels horizontally in a loop around two rollers with vertically oriented axes, which are separated by 7.5 meters. This belt device is mounted inside a large water tank with the water level set just below the top edge of the belt. The belt, rollers, and supporting frame are contained within a sheet metal box to keep the device dry except for one 6-meter-long straight test section between rollers. The belt is launched from rest with an acceleration of up to 3-g in order to quickly reach steady state velocity. This creates a temporally evolving boundary layer analogous to the spatially evolving boundary layer created along a flat-sided ship moving at the same velocity, with a length equivalent to the length of belt that has passed the measurement region since the belt motion began. Surface profile measurements in planes normal to the belt surface are conducted using cinematic Laser Induced Fluorescence and quantitative surface profiles are extracted at each instant in time. Using these measurements, free surface fluctuations are examined and the propagation behavior of these free surface ripples is studied. It is found that free surface fluctuations are generated in a region close to the belt surface, where sub-surface velocity fluctuations influence the behavior of these free surface features. These rapidly-changing surface features close to the belt appear to lead to the generation of freely-propagating waves far from the belt, outside the influence of the boundary layer. Sub-surface PIV measurements are performed in order to study the modification of the boundary layer flow field due to the effects of the water free surface. Cinematic planar PIV measurements are performed in horizontal planes parallel to the free surface by imaging the flow from underneath the tank, providing streamwise and wall-normal velocity fields. Additional planar PIV experiments are performed in vertical planes parallel to the belt surface in order to study the bahvior of streamwise and vertical velocity fields. It is found that the boundary layer grows rapidly near the free surface, leading to an overall thicker boundary layer close to the surface. This rapid boundary layer growth appears to be linked to a process of free surface bursting, the sudden onset of free surface fluctuations. Cinematic white light movies are recorded from beneath the water surface in order to determine the onset location of air entrainment. In addition, qualitative observations of these processes are made in order to determine the mechanisms leading to air entrainment present in this flow.

Guided Migration and Collective Behavior: Cell Dynamics during Cancer Progression

This dissertation focuses on gaining understanding of cell migration and collective behavior through a combination of experiment, analysis, and modeling techniques. Cell migration is a ubiquitous process that plays an important role during embryonic development and wound healing as well as in diseases like cancer, which is a particular focus of this work. As cancer cells become increasingly malignant, they acquire the ability to migrate away from the primary tumor and spread throughout the body to form metastatic tumors. During this process, changes in gene expression and the surrounding tumor environment can lead to changes in cell migration characteristics. In this thesis, I analyze how cells are guided by the texture of their environment and how cells cooperate with their neighbors to move collectively. The emergent properties of collectively moving groups are a particular focus of this work as collective cell dynamics are known to change in diseases such as cancer. The internal machinery for cell migration involves polymerization of the actin cytoskeleton to create protrusions that---in coordination with retraction of the rear of the cell---lead to cell motion. This actin machinery has been previously shown to respond to the topography of the surrounding surface, leading to guided migration of amoeboid cells. Here we show that epithelial cells on nanoscale ridge structures also show changes in the morphology of their cytoskeletons; actin is found to align with the ridge structures. The migration of the cells is also guided preferentially along the ridge length. These ridge structures are on length scales similar to those found in tumor microenvironments and as such provide a system for studying the response of the cells' internal migration machinery to physiologically relevant topographical cues. In addition to sensing surface topography, individual cells can also be influenced by the pushing and pulling of neighboring cells. The emergent properties of collectively migrating cells show interesting dynamics and are relevant for cancer progression, but have been less studied than the motion of individual cells. We use Particle Image Velocimetry (PIV) to extract the motion of a collectively migrating cell sheet from time lapse images. The resulting flow fields allow us to analyze collective behavior over multiple length and time scales. To analyze the connection between individual cell properties and collective migration behavior, we compare experimental flow fields with the migration of simulated cell groups. Our collective migration metrics allow for a quantitative comparison between experimental and simulated results. This comparison shows that tissue-scale decreases in collective behavior can result from changes in individual cell activity without the need to postulate the existence of subpopulations of leader cells or global gradients. In addition to tissue-scale trends in collective behavior, the migration of cell groups includes localized dynamic features such as cell rearrangements. An individual cell may smoothly follow the motion of its neighbors (affine motion) or move in a more individualistic manner (non-affine motion). By decomposing individual motion into both affine and non-affine components, we measure cell rearrangements within a collective sheet. Finally, finite-time Lyapunov exponent (FTLE) values capture the stretching of the flow field and reflect its chaotic character. Applying collective migration analysis techniques to experimental data on both malignant and non-malignant human breast epithelial cells reveals differences in collective behavior that are not found from analyzing migration speeds alone. Non-malignant cells show increased cooperative motion on long time scales whereas malignant cells remain uncooperative as time progresses. Combining multiple analysis techniques also shows that these two cell types differ in their response to a perturbation of cell-cell adhesion through the molecule E-cadherin. Non-malignant MCF10A cells use E-cadherin for short time coordination of collective motion, yet even with decreased E-cadherin expression, the cells remain coordinated over long time scales. In contrast, the migration behavior of malignant and invasive MCF10CA1a cells, which already shows decreased collective dynamics on both time scales, is insensitive to the change in E-cadherin expression.

Guided Migration and Collective Behavior: Cell Dynamics during Cancer Progression

This dissertation focuses on gaining understanding of cell migration and collective behavior through a combination of experiment, analysis, and modeling techniques. Cell migration is a ubiquitous process that plays an important role during embryonic development and wound healing as well as in diseases like cancer, which is a particular focus of this work. As cancer cells become increasingly malignant, they acquire the ability to migrate away from the primary tumor and spread throughout the body to form metastatic tumors. During this process, changes in gene expression and the surrounding tumor environment can lead to changes in cell migration characteristics. In this thesis, I analyze how cells are guided by the texture of their environment and how cells cooperate with their neighbors to move collectively. The emergent properties of collectively moving groups are a particular focus of this work as collective cell dynamics are known to change in diseases such as cancer. The internal machinery for cell migration involves polymerization of the actin cytoskeleton to create protrusions that---in coordination with retraction of the rear of the cell---lead to cell motion. This actin machinery has been previously shown to respond to the topography of the surrounding surface, leading to guided migration of amoeboid cells. Here we show that epithelial cells on nanoscale ridge structures also show changes in the morphology of their cytoskeletons; actin is found to align with the ridge structures. The migration of the cells is also guided preferentially along the ridge length. These ridge structures are on length scales similar to those found in tumor microenvironments and as such provide a system for studying the response of the cells' internal migration machinery to physiologically relevant topographical cues. In addition to sensing surface topography, individual cells can also be influenced by the pushing and pulling of neighboring cells. The emergent properties of collectively migrating cells show interesting dynamics and are relevant for cancer progression, but have been less studied than the motion of individual cells. We use Particle Image Velocimetry (PIV) to extract the motion of a collectively migrating cell sheet from time lapse images. The resulting flow fields allow us to analyze collective behavior over multiple length and time scales. To analyze the connection between individual cell properties and collective migration behavior, we compare experimental flow fields with the migration of simulated cell groups. Our collective migration metrics allow for a quantitative comparison between experimental and simulated results. This comparison shows that tissue-scale decreases in collective behavior can result from changes in individual cell activity without the need to postulate the existence of subpopulations of leader cells or global gradients. In addition to tissue-scale trends in collective behavior, the migration of cell groups includes localized dynamic features such as cell rearrangements. An individual cell may smoothly follow the motion of its neighbors (affine motion) or move in a more individualistic manner (non-affine motion). By decomposing individual motion into both affine and non-affine components, we measure cell rearrangements within a collective sheet. Finally, finite-time Lyapunov exponent (FTLE) values capture the stretching of the flow field and reflect its chaotic character. Applying collective migration analysis techniques to experimental data on both malignant and non-malignant human breast epithelial cells reveals differences in collective behavior that are not found from analyzing migration speeds alone. Non-malignant cells show increased cooperative motion on long time scales whereas malignant cells remain uncooperative as time progresses. Combining multiple analysis techniques also shows that these two cell types differ in their response to a perturbation of cell-cell adhesion through the molecule E-cadherin. Non-malignant MCF10A cells use E-cadherin for short time coordination of collective motion, yet even with decreased E-cadherin expression, the cells remain coordinated over long time scales. In contrast, the migration behavior of malignant and invasive MCF10CA1a cells, which already shows decreased collective dynamics on both time scales, is insensitive to the change in E-cadherin expression.

Experimental characterization of wingtip vortices using smoke flow visualizations

In order to predict the axial development of the wingtip vortices strength an accurate theoretical model is required. Several experimental techniques have been used to that end, e.g. PIV or hotwire anemometry, but they imply a significant cost and effort. For this reason, we have carried out experiments using the smoke-wire technique to visualize smoke streaks in six planes perpendicular to the main stream flow direction. Using this visualization technique, we obtained quantitative information regarding the vortex velocity field by means of Batchelor's model~\cite{batchelor}, which only depends on two free parameters, i.e. the vortex strength, $S$, and the virtual origin, $z_0$. Results for two chord based Reynolds numbers have been compared with those provided by del Pino et at. (2011), finding good agreement.

Teste do bulbo molhado para o plantio de cana-de-açúcar com irrigação localizada.

No Submédio do Vale do São Francisco, o sistema de cultivo da cana-de-açúcar (Saccharum spp.) é baseado no fornecimento da água durante todo o seu ciclo. Nesta região, a irrigação na cana-de-açúcar tem sido feita por sulcos, aspersão (pivô central e linear) e por gotejamento subsuperficial, os quais proporcionam índices variáveis de eficiência no uso de água pela cultura. Dentre eles, o gotejamento subsuperficial é o mais eficiente, uma vez que disponibiliza água próximo ao sistema radicular e facilita a automação do sistema para irrigação e fertirrigação durante o ciclo da cultura.

Aplicação de modelo agrometeorológico espectral no perímetro irrigado da bacia do São Francisco, utilizando imagens RAPIDEYE.

O objetivo do trabalho foi aplicar o modelo SAFER (Simple Algorithm For Evapotranspiration Retrieving) com a finalidade de analisar os parâmetros biofísicos na área do Perímetro Irrigado de Jaíba, na Bacia do São Francisco. Foram obtidos dados meteorológicos e imagens do satélite RapidEye (resolução de 5m), referente aos dias 26 de junho de 2013 e 29 de abril de 2014. Os valores médios diários do Índice de Vegetação por Diferença Normalizada (NDVI) foram 0,29±0,16 e 0,43±0,18, para 2013 e 2014, respectivamente. Na imagem de 2013 foram observados valores superiores de temperatura da superfície (Ts) (303,08±2,26 K) aos observados em 2014 (296,14±2,32 K). A evapotranspiração (ET) média diária de toda a cena de 2013 foi 0,43±0,96 mm e valor máximo de 6,11. Em 2014, os valores de ET médios diários foram de 2,19±2,01mm. Conforme estudos anteriores, a caatinga converte a maior parte da energia disponível em calor sensível (H), enquanto as culturas irrigadas apresentam altos valores de ET. Com imagens de alta resolução espacial, sem a banda termal, foi possível obter os parâmetros biofísicos da superfície possibilitando o monitoramento em nível de pivô central e talhões de culturas irrigadas, auxiliando o uso racional da água em tempos de deficiência hídrica.

Experimental determination of burning velocity in metal dust explosions

The modeling of metal dust explosion phenomenon is important in order to safeguard industries from potential accidents. A key parameter of these models is the burning velocity, which represents the consumption rate of the reactants by the flame front, during the combustion process. This work is focused on the experimental determination of aluminium burning velocity, through an alternative method, called "Direct method". The study of the methods used and the results obtained is preceded by a general analysis on dust explosion phenomenon, flame propagation phenomenon, characteristics of the metals combustion process and standard methods for determining the burning velocity. The “Direct method” requires a flame propagating through a tube recorded by high-speed cameras. Thus, the flame propagation test is carried out inside a vertical prototype made of glass. The study considers two optical technique: the direct visualization of the light emitted by the flame and the Particle Image Velocimetry (PIV) technique. These techniques were used simultaneously and allow the determination of two velocities: the flame propagation velocity and the flow velocity of the unburnt mixture. Since the burning velocity is defined by these two quantities, its direct determination is done by substracting the flow velocity of the fresh mixture from the flame propagation velocity. The results obtained by this direct determination, are approximated by a linear curve and different non-linear curves, which show a fluctuating behaviour of burning velocity. Furthermore, the burning velocity is strongly affected by turbulence. Turbulence intensity can be evaluated from PIV technique data. A comparison between burning velocity and turbulence intensity highlighted that both have a similar trend.

Caratterizzazione fluidodinamica di un digestore anaerobico modello tramite tecniche di diagnostica ottica

L’aumento del consumo di energia globale e le problematiche legate all’inquinamento stanno rendendo indispensabile lo spostamento verso fonti di energia rinnovabile. La digestione anaerobica rappresenta una possibile soluzione in quanto permette di produrre biogas da biomassa organica di scarto ma, l’ottimizzazione del processo risulta difficoltosa a causa delle numerose variabili chimiche, biologiche, fisiche e geometriche correlate. Nel presente elaborato, concentrandosi sulle problematiche relative alla miscelazione interna, è stata investigata la fluidodinamica interna di un reattore modello ottenuto tramite scale-down di un digestore anaerobico industriale che presentava problemi di sedimentazione di sostanza solida sul fondo del reattore. Tramite tecniche di diagnostica ottiche, è stato studiato il movimento del fluido, prima utilizzando acqua demineralizzata e poi una soluzione di gomma di xantano come fluido di processo, al fine di studiare il campo di moto medio interno al reattore. Le tecniche utilizzate sono la Particle Image Velocimetry (PIV) e la Planar Laser Induced Fluorescence (PLIF). Al fine di rendere il sistema investigato il più rappresentativo possibile del digestore industriale, è stato utilizzato come fluido di processo per alcune delle prove raccolte, una soluzione acquosa 1,0g/kg di gomma di xantano, le cui proprietà reologiche sono state investigate grazie ad un Reometro Anton Paar MCR 301.