Les appareils de chauffage électrique, qui peuvent paraître relativement simples au premier abord car constitués uniquement d’une résistance chauffante électrique encapsulée dans une enveloppe métallique, sont en réalité des échangeurs de chaleur beaucoup plus complexes. Outre la partie régulation, en charge de déterminer à chaque instant la quantité d’énergie à apporter à la pièce pour fournir les températures d’air souhaitées, l’appareil doit assurer une uniformité des températures et des vitesses d’air cohérentes avec le confort thermique désiré et ce, quels que soient son mode de fonctionnement et les conditions thermiques extérieures. De cette bonne répartition des températures et des vitesses d’air découlera un bon niveau de confort thermique, gage d’une consommation énergétique sobre et maîtrisée. L’objectif de la thèse est donc de mieux comprendre dans une première phase les phénomènes thermo-aérauliques agissant à l’échelle du radiateur et dans une deuxième phase ceux agissant à l’échelle de la pièce. Pour améliorer cette compréhension, un outil de simulation numérique qui pourra servir à la conception des radiateurs par la société CAMPA a été développé. / The electric heating devices, which can seem relatively simple at first sight because composed only by an electric heating resistance in a metallic box, are in reality much more complex heat exchangers. Besides the regulation process part the role of which is to determine at every moment the quantity of energy to bring to the room to supply the desired temperatures of air, the device has to ensure a uniformity of temperatures and velocities of air in agreement with the thermal comfort wished, whatever his way of functioning and the outside thermal conditions. This good distribution of temperatures and velocities of air will give a good thermal comfort level which is the condition of a sober and controlled energy consumption. The objective of this thesis is thus to better understand in a first phase the thermo-aeraulics phenomena acting on the scale of the radiator and in the second phase those acting on the scale of the room. To improve this understanding, a tool of digital simulation which can be used to the conception of radiators by the company CAMPA has been developed.

Ce travail est consacré à l'étude expérimentale des écoulements diphasiques et triphasiques d'inclusions (bulles, gouttes, sphères) en milieux tant newtoniens que non newtoniens à l'échelle microscopique et mésoscopique, en utilisant la visualisation par une caméra rapide, la vélocimétrie par images des particules (PIV) ainsi que la micro-vélocimétrie par images des particules. Des bulles et des gouttes ont été étudiées expérimentalement depuis leur formation, en passant par leur déformation jusqu'à leur coalescence. La formation de bulles dans des micro-mélangeurs a été étudiée et caractérisée par l'obtention de champs de vitesses. Différents paramètres, tels que le cisaillement, la géométrie de la zone de formation, les débits ou encore les propriétés physiques ont été testés afin de développer des lois d'échelles. La traversée d'une interface liquide-liquide par une inclusion a été abordée par des expériences originales, permettant de décrire la dynamique du phénomène, de définir des nombres adimensionnels et de mettre en évidence des instabilités interfaciales. L'effet Weissenberg a également été étudié aux différentes échelles afin de comprendre les phénomènes conduisant à son amplification. Enfin, en milieu viscoélastique et rhéofluidifiant, nous avons caractérisé l'écoulement autour d'une inclusion isolée solide par l'obtention de champs de vitesses. Ces résultats ont permis de confirmer l'origine viscoélastique du sillage négatif et de prédire ses caractéristiques / The present work was devoted to the experimental study of the multiphase flow around inclusions in both Newtonian and non-Newtonian media at respectively microscopic and mesoscopic scales, by means of the Particle Image Velocimetry (both PIV and µ-PIV) and fast camera visualization. Bubbles and drops were experimentally studied starting from their formation, the rising and up to their coalescence and fragmentation. Bubble formation in micro-mixers was also investigated and characterized by measuring the liquid velocity fields. Different parameters, such as the shear rate, the geometry of the micro-mixer, the flow rates or the physical properties were tested to develop correlations of power-law kind. The deformation of a liquid-liquid interface due to the passage of an inclusion was investigated by original experiments in order to observe and describe the dynamics of the phenomenon, to define the reliable dimensionless numbers and also to highlight several interfacial instabilities. The Weissenberg effect was also studied at different scales in various non-Newtonian fluids in comparison with Newtonian fluids to understand the amplification phenomena under the combining effects of instability and normal forces. Finally, the flow around an isolated solid inclusion was characterized by performing the measurements of velocity fields in viscoelastic and shear-thinning fluids. These results were used to confirm the viscoelastic origin of the negative wake behind the solid sphere and to model its characteristics

Ce travail vise à développer une approche originale à micro et à méso-échelle pour étudier divers phénomènes et intensifier les performances du réacteur. A méso-échelle, l'accent est mis sur l'efficacité de la production de biogaz dans un réacteur anaérobie 2D sous différentes conditions hydrodynamiques ainsi qu’à différentes concentrations de substrat. Puis, dans un dispositif microfluidique transparent, une seule granule de différentes tailles a été utilisée sous différentes conditions d'exploitation. Les effets des différentes conditions hydrodynamiques et des concentrations de substrat associés à la taille et la densité des granules de boues sur la production de biogaz ont été étudiés / The present work is focused on developing an original micro to mesoscale approach to investigate various phenomena and then to intensify the performance of a reactor. At mesoscale, the emphasis is given to the interactions between granular sludge particles as well as the biogas production efficiency in a 2D reactor under various hydrodynamic conditions at different concentrations of substrate. Then, within the microdevices, a single sludge particle of various sizes was used under different operating conditions such as superficial liquid velocity and concentration of substrate. The effect of different hydrodynamic conditions and concentration of substrate was studied

An experimental study of the flow behavior inside the channels of an 8-blade backswept low specific speed impeller at design and off-design conditions is presented. The measurements took place at both the inlet and the outlet of the impeller channel at the mid height of the channel passage. The particle image velocimetry (PIV) technique was used to measure the velocity components in the inlet and outlet frames of the impeller channel. The flow behavior inside the channel, the mean normalized primary and secondary velocity components at six radial locations inside the channels, and turbulence intensity in terms of the variation in the relative velocity components were investigated at the design condition, 75%, 50%, 40%, 30% and 25% of the design flow rate. The results demonstrated a well behaved flow with no evidence of flow separation at the design condition. The fluid flow inside the impeller channel started experiencing a flow separation, when the flow rate is reduced, which propagated throughout the channel passage and caused the channel to stall with a large recirculation zone at severe off-design flow rates.

An experimental study of the flow behavior inside the channels of an 8-blade backswept low specific speed impeller at design and off-design conditions is presented. The measurements took place at both the inlet and the outlet of the impeller channel at the mid height of the channel passage. The particle image velocimetry (PIV) technique was used to measure the velocity components in the inlet and outlet frames of the impeller channel. The flow behavior inside the channel, the mean normalized primary and secondary velocity components at six radial locations inside the channels, and turbulence intensity in terms of the variation in the relative velocity components were investigated at the design condition, 75%, 50%, 40%, 30% and 25% of the design flow rate. The results demonstrated a well behaved flow with no evidence of flow separation at the design condition. The fluid flow inside the impeller channel started experiencing a flow separation, when the flow rate is reduced, which propagated throughout the channel passage and caused the channel to stall with a large recirculation zone at severe off-design flow rates.

This work examines the ability of two dimensional CFD models to predict the unsteady flow downstream of a cylinder, with and without fairing, in uniform flow. PIV measurements of the flow-field downstream of the cylinder and fairing in uniform flow are first presented. “Slices” of the flow at several locations along the cylinder are compared to show the variation of the flow in the cross-stream direction. Then the PIV flow is compared with RANS and LES simulations of the flow. Velocity time histories are compared and hydrodynamic coefficients are discussed. In a general sense, two dimensional CFD can give a functional approximation of the unsteady flow field downstream of the cylinder or fairing. / text

Particle image velocimetry (PIV) is a widely used fluid measurement technique. Three dimensional PIV data or stereo PIV is acquired using two cameras. Stereo cameras are calibrated from camera coordinates, pixels, to real world units such as millimeters using calibration models. Stereo calibration is fundamental to the accuracy of a PIV measurement. In this thesis, the accuracy of the stereo calibration is assessed. The mean error of stereo calibration was found to be 0.23%.

This research paper highlights the significance of mock circulatory loops in aiding the development and testing of left ventricle assist devices (LVADs). Heart disease is the leading cause of death in America, and LVAD offers an effective solution to patients with severe coronary artery disease who are not eligible for heart transplants. However, before testing LVADs in-vivo, extensive performance and reliability testing is required as per Food and Drug Administration guidelines. Mock circulatory loops are useful for simulating the cardiac cycle and capturing pressure and flow meter readings. The research focused on developing and testing a mock circulatory loop that accurately captures pressure and flow meter readings. The team experimented with various silicone elastomers and a urethane-based material, ClearFlex 30, to create a transparent phantom. The report highlights the importance of surface roughness for optical clarity, with an average surface roughness of 0.186 μ being ideal for optimal clarity achieved with 800-grit sandpaper. The impact of pressure differences between the aortic and mitral inlet/outlets was also studied, and it was found that the loop's resistance can be modified to achieve elevated pressure in the aortic outlet. The report further emphasized the importance of refractive index matching to perform particle image velocity. Matching the refractive index of the phantom with the medium is critical to avoid distortion and refraction of the light. Glycerol water was found to be an effective medium for refractive index matching. Overall, the successful testing of the mock circulatory loop provides valuable insights into the flow structure within the heart, aiding in the development of future LVADs. This research is significant in advancing the cardiology field and will potentially benefit many patients suffering from heart disease. / Master of Science / This research paper focuses on developing and testing left ventricle assist devices (LVADs) using a mock circulatory loop tool. Heart disease is a leading cause of death in America, and LVADs provide an effective solution for patients with severe coronary artery disease who are not eligible for heart transplants. However, before testing LVADs on humans, extensive performance and reliability testing is required as per Food and Drug Administration guidelines. Mock circulatory loops are a tool that helps simulate the cardiac cycle and capture pressure and flow meter readings. The researchers developed and tested a mock circulatory loop that could accurately capture pressure and flow meter readings. They used various materials to create a transparent phantom that allowed them to see inside the loop. The researchers found that the surface roughness of the phantom was important for optical clarity, and they achieved optimal clarity using 800-grit sandpaper. They also studied the impact of pressure differences between the aortic and mitral inlet/outlets. They found that the loop's resistance can be modified to achieve elevated pressure in the aortic outlet. To study the flow structure within the heart, the researchers used a technique called particle image velocity. They emphasized the importance of refractive index matching, which helps avoid distortion and refraction of light. The researchers found that glycerol water was an effective medium for refractive index matching. Overall, the successful testing of the mock circulatory loop provides valuable insights into the flow structure within the heart, aiding in the development of future LVADs. This research has significant implications for advancing the cardiology field and potentially benefitting many patients suffering from heart disease.

In particle image velocimetry (PIV) the measurement signal is contained in the recorded intensity of the particle image pattern superimposed on a variety of noise sources. The inherent amount of signal mutual information between consecutive images governs the strength of the resulting PIV cross correlation and ultimately the accuracy and uncertainty of the produced PIV measurements. Hence we posit that the correlation signal-to-noise-ratio (SNR) metrics calculated from the correlation plane can be used to quantify the quality of the correlation and the resulting uncertainty of an individual measurement. A new SNR metric termed "mutual information" (MI) which quantifies the amount of common information (particle pattern) between two consecutive images is also introduced and investigated. This measure provides a direct estimation of the apparent NIFIFO parameter of an image pair providing an alternative approach towards uncertainty estimation but also connecting the current development to one of the most fundamental principles of PIV and the previous established theory. We extend the original work by Charonko and Vlachos and present a framework for evaluating the correlation strength using a set of different metrics, which in turn are used to develop models for uncertainty estimation. Several corrections have been applied in this work. The metrics and corresponding models presented herein are expanded to be applicable to both standard and filtered correlations by applying a subtraction of the minimum correlation value to remove the effect of the background image noise. In addition, the notion of a "valid" measurement is redefined with respect to the correlation peak width in order to be consistent with uncertainty quantification principles and distinct from an "outlier" measurement. Finally the type and significance of the error distribution function is investigated. These advancements lead to robust uncertainty estimation models, which are tested against both synthetic benchmark data as well as actual experimental measurements. In this work, U68.5 uncertainties are estimated at the 68.5% confidence level while U95 uncertainties are estimated at 95% confidence level. For all cases the resulting calculated coverage factors approximate the expected theoretical confidence intervals thus demonstrating the applicability of these new models for estimation of uncertainty for individual PIV measurements. / Master of Science

The interaction of a rectangular turbulent jet with a free surface for three jet-exit aspect ratios is experimentally investigated using Particle Image Velocimetry (PIV). The jet exits from a sharp edged rectangular orifice plate, parallel to the free surface and has a jet width of d = 10 mm. Aspect ratios of 1, 2 and 4 are studied with a fixed offset of 3d from the free surface. Reynolds and Froude numbers based on the bulk velocity are 6900 and 1.27 respectively. Detailed 2-D velocity fields are captured using the PIV in the central x-y plane for 0 < x/d < 23.5. The distribution of Reynolds shear stresses and turbulent kinetic energy show that they are suppressed in the vicinity of the free surface due to confinement. There was a significant effect of nozzle geometry on the reattachment point and recirculation region of the jets. / May 2016