Für zahlreiche technische Prozesse ist die Kenntnis des Schlupfes bzw. des Drift-Fluxes in Zweiphasenströmungen notwendig. Beispiele sind die Bestimmung der Druckverluste sowie der Wärme- und Stoffübertragungsvorgänge in Verdampfern oder Kondensatoren, der Phasenverweilzeit in chemischen Reaktoren sowie der Moderatorwirkung des zweiphasigen Kühlmittels innerhalb des Kerns eines Siedewasserreaktors.

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Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

A study was conducted to investigate the effect of magnetic devices on the precipitates in a condenser’s tubes when seawater is used as cooling water. This test was necessary to evaluate these devices as possible replacements for conventional methods of water treatment. In the test program, a small condenser was operated with conditions similar to utility condensers. This condenser was modified to include twelve tubes. The inlet water box was divided to provide for two parallel magnetic water treatment streams, and one control untreated water stream for comparison purposes. With and without the use of a magnetic device, the chemical analysis and the thickness of the deposits showed no significant difference. The only difference that was observed in these deposits was their crystallogical structure. When the magnetic device was in place, deposits were flaky (powder-like), chipped, and showed no strong adhesion to the inner surface of the condenser’s tubes. Without the use of a magnetic device, deposits were flocculated, hard, and crusty. This thesis proposes a theory which may help explain the differences in the deposits. The theory will include homogenous nucleation to explain the physical changes of the deposits. The discussion will also postulate how well the magnetic energy improved the homogenous nucleation process. A method of analysis is proposed which demonstrates how the critical radius of a nucleus is affected by a magnetic field.

Phase-change heat transfer involves the exchange of thermal energy when a substance transitions between different phases, such as solid to liquid (melting), liquid to vapor (boiling), or vice versa. During phase-change, energy is absorbed or released without a change in temperature. In particular, boiling is highly efficient due to the large latent heat of vaporization, allowing for dissipative heat fluxes on the order of q′′ ∼ 10–100 W/cm². However, during boiling, once the temperature exceeds a critical threshold, a vapor film forms between the heated surface and the liquid, suppressing effective nucleate boiling which reduces heat transfer efficiency so that q′′ ∼ 1 W/cm². This critical temperature limitation prompted our exploration of three-phase heat transfer. In three-phase heat transfer, energy is transferred between the solid, liquid, and vapor phases; all of which coexist simultaneously. In this study, we define and investigate three-phase heat transfer by examining ice on a superheated substrate. We explore the use of ice as a quenchant and our findings indicate that dissipative heat fluxes for our three-phase system are an order of magnitude larger than for classical boiling (q′′ ∼ 1,000 W/cm²). This is due to the inherent 100 °C temperature differential across the meltwater film, which dissipates q′′ ∼ 100 W/cm² via conduction (and subsequent ice melting) and an additional q′′ ∼ 100 W/cm² for sensible heating of the meltwater. We propose experiments to measure the dissipative heat flux of a tall and pressurized ice column during three-phase heat transfer. Furthermore, we discuss potential avenues for future research of three-phase heat transfer at high superheats. / Master of Science / Phase-change heat transfer involves the exchange of heat when a substance transitions between different phases, such as solid to liquid (melting), liquid to vapor (boiling), or vice versa. During phase-change, energy is absorbed or released without a change in temperature. For example, in boiling, water molecules act like tiny magnets. When water changes from one phase to another, the distance between these tiny magnets changes. When they are pulled apart, like when water turns into steam, they need some extra energy to do that. This energy, termed latent heat, is the reason lots of heat can be transferred during phase-change. However, during boiling, once the temperature of the heated surface exceeds a critical threshold, a vapor film forms between the heated surface and the liquid, which suppresses effective boiling and reduces the efficiency. This critical temperature limitation prompted our exploration of three-phase heat transfer. In three-phase heat transfer, energy is transferred between the solid, liquid, and vapor phases; all of which coexist simultaneously. In this study, we define and investigate three-phase heat transfer by observing ice on a heated surface. The vapor film is avoided for a while because a majority of the heat is used to melt the ice and warm the meltwater, leaving only a little left for vaporization. We propose experiments to measure the heat transfer capabilities of a tall ice column pressed into a heated surface. Furthermore, we discuss potential avenues for future research of three-phase heat transfer at high superheats.

Passive samplers can be used to determine time-integrated patterns of water chemistry at one or many locations throughout a stream network while minimizing cost and sampling time. A passive flux meter (PFM) simultaneously estimates time-averaged water and solute mass fluxes in flowing water. PFMs have been used in groundwater to quantify contaminant flux but have been used only very recently in streams. In this study, PFMs were deployed in the surface and subsurface of headwater stream channels to examine the efficacy of the device to quantify mean concentrations of calcium, aluminum, and sulfur in streams of the Hubbard Brook Experimental Forest in New Hampshire, USA. In general, the PFM estimates of surface and subsurface stream chemistry were more accurate when flow rates were higher and more water passed through the PFM. During the lowest flows, PFMs overpredicted concentrations by 50 to 800%. In estimating calcium concentrations, 5 PFMs were within 10% of grab sample concentrations and 7 PFMs were within 30% of grab sample concentrations out of a total of 35 comparisons. Likewise, for sulfur concentrations, 4 PFMs were within 10% of grab sample concentrations and 7 PFMs were within 30% of grab sample concentrations out of 35 comparisons. Concentrations of aluminum were too low to be quantified above 90% confidence. PFMs calculated a lower cumulative discharge through the surface water PFMs than through the subsurface which may be explained by flow divergence around the sampler. Changes to PFM design and shorter deployment times are proposed to increase the efficacy of the PFM. / Master of Science / Passive sampling of headwater streams has advantages over traditional water sampling in quantifying stream water chemistry over time and space, while minimizing cost and sampling time. A passive flux meter (PFM) is a sampler that estimates local time-averaged discharge of water and time-averaged solute amount in flowing water without the need for constant monitoring, maintenance, or power sources. PFMs have been used in groundwater systems to quantify contaminant concentrations but have only been used very recently in streams or in the sediments below streams. In this study, PFMs were installed in headwater streams and the shallow sediments below the streams to examine the ability of the device to quantify the natural water chemistry. Concentrations of calcium, aluminum, and sulfate were evaluated in streams of the Hubbard Brook watershed in New Hampshire, USA. Concentrations of aluminum were too low to be quantified. In general, the PFM estimates of surface and subsurface stream chemistry were more accurate when flow rates were higher and more water passed through the PFM. During the lowest flows, PFMs overestimated stream concentrations. PFMs installed in small streams measured more total volume through the device than PFMs installed in sediments below the streams. PFM design may have had an impact on these results. Changes to PFM design and shorter deployment times are proposed to increase the efficacy of the PFM

Aquatic plants or macrophytes are known as conduits of Methane (CH4), Carbon dioxide (CO2) and Nitrous oxide (N2O) which contribute to the total fluxes of the Greenhouse gases emissions from lakes. Recent studies emphasized that the knowledge on plant mediated emissions calls for more systematic and comparative data especially in the areas of spatial and temporal variability. In this study I measured diel (24 hour) and diurnal(  daily hours only) plant mediated fluxes during four sampling sessions using chamber method from a  Swedish lake in summer 2012. The measurements were conducted on two macrophyte population patterns of mixed plant communities and Equisetum fluviatile (specie-specific) community. CH4 emissions were higher in darker hours and there were no diel correlation between CH4 fluxes and average diel temperature. CH4 fluxes varied between 0.42 mmol m-2d-1 and 2.3 mmol m-2d-1. The CO2 fluxes had negative fluxes in day and positive during the day which was logical due to macrophyte respiration and photosynthesis mechanisms. Occasional daily positive fluxes were seen (only) during the rainy hours and there were no correlation between temperature and diel CO2 fluxes. The total net CO2 exchange was 2.8mmol m-2d-1 indicating that there was more CO2 release in the littoral zone of that lake. N2O fluxes did not show any clear diel or monthly pattern and the fluxes ranged between positive and negative numbers. The N2O fluxes did not exceed 2µmol m-2 d-1 with the total average flux of 0.8µmol m-2 d-1.

Boreal old-growth forests are key determinants in the global carbon cycle. It is unknown how the role of persistent old-growth forests will be in the carbon cycle in the face of predicted climatic changes. Eddy-covariance measurements are commonly used to quantify carbon exchange between ecosystems, such as forests, and the atmosphere. Error due to gap-fill method is of particular interest in these datasets. Here we filled a 15-year eddy covariance dataset from the Northern Old-Growth Boreal Black Spruce (Picea mariana) site located near Thompson, in central Manitoba, Canada using four different gap-fill methods. Our objectives were to determine if choice of gap-fill method affected annual NEP and if these errors compounded to even greater differences over the 15-year study period. Most significant differences in NEP among methods occurred from September to December, but variations during the growing season were responsible for most of the annual differences. / October 2016

The thermal boundary condition to a fire exposed surface was quantified with a hybrid heat flux gage. Methods were developed to determine the net heat flux through the gage, incident heat flux, cold surface heat flux, convective heat transfer coefficient, adiabatic surface temperature, and the separated components of radiative and convective heat flux. Experiments were performed in a cone calorimeter with the hybrid gage flush mounted into UNIFRAX Duraboard LD ceramic board. The results were then compared to results obtained with a Schmidt-Boelter gage and a plate thermometer. The hybrid heat flux gage predicted a cold surface heat flux within 5% of cold surface heat fluxes measured with a Schmidt-Boelter gage. Adiabatic surface temperature measurements compared well with the plate thermometer measurements at steady state. Hybrid gage measurements were performed on flat plate samples of Aluminum 5083, Marinite P, and UNIFRAX Duraboard LD ceramic board. The gage and sample assemblies were exposed to mixed-mode heat transfer conditions in a cone calorimeter. Temperature measurements were performed at the top, center, bottom surfaces of the marinite and ceramic board samples. A single midpoint temperature was performed on the aluminum. Boundary condition details obtained with the hybrid gage were then input to the commercial finite element analysis package Abaqus. Abaqus was used to create the flat plate geometries of the sample and variable temperature dependent material properties were used for each material. Measured temperatures were then compared to the model predicted temperatures with good results. Hybrid gage measurements were verified using a new experimental apparatus. The apparatus consisted of an impinging jet assembly, a tungsten lamp, and a gage holster assembly. The impinging jet was used to expose the gage to isolated convection and the lamp was used to expose the gage to isolated radiation. The gage holster assembly was used to water cool the gage when desired. Measurements performed with the gage water cooled in isolated convection allowed for the convective heat transfer coefficient to be determined. Two methods were developed to determine the convective heat transfer coefficient in mixed-mode heat transfer conditions. These methods were then verified by comparison to the isolated heat transfer coefficient. Similarly, the incident radiation was isolated by water cooling the gage while only the lamp was on. The components of heat flux were then separated for mixed-mode comparisons and were verified against this isolated radiation. The hybrid gage predicted convective heat transfer coefficients within 10% of the isolated heat transfer coefficient and incident heat fluxes within 11% of the isolated radiation. / Master of Science

Les anticorps (Ac) marqués à l'aide de phthalocyanines (Pc) ont un grand potentiel d'applications pour des essais d'immunofluorescence tout comme pour la thérapie photodynamique (PDT). La PDT est une forme relativement nouvelle de traitement du cancer ou d'autres maladies bénignes tel le psoriasis. Cette technique implique l'administration et l'activation par la lumière d'un photosensibilisateur localisé préférentiellement au niveau des cellules cancéreuses ou en croissance intense. La plupart des photosensibilisateurs utilisés pour la PDT sont de type porphyrine tels les Pcs. Dans cette étude, nous utilisons différentes phthalocyanines hautement solubles dans l'eau. Notre étude est basée sur l'utilisation d'anticorps monoclonaux comme vecteur des Pcs et comporte deux volets distincts. Tout d'abord l'utilisation des Pcs comme fluorochrome et finalement l'utilisation des complexes OKT3-AlPcS[indice inférieur 3]A[indice inférieur 1] dans l'amélioration de la PDT. Les Pcs sont liés de façon covalente aux Ac monoclonaux via une chaîne carboxy activée du Pc par la méthode de carbodiimide/N-hydroxysulfosuccinimide. Le complexe OKT3-AlPcS[indice inférieur 3]A[indice inférieur 1] lié à l'antigène de la surface cellulaire des cellules Jurkat CD3+ est visualisé par un trieur en cryométrie de flux (FACSCAN) et la phototoxicité in vitro est déterminée par un essai colorimétrique (test MTT). Nous avons donc produit un Ac de très bonne pureté et confirmé par cryométrie de flux la conservation de l'activité et de la spécificité de la liaison de l'Ac pour le récepteur après liaison covalente avec le Pc. Nous sommes ainsi les premiers à proposer l'utilisation des Pcs comme fluorochrome. Nous avons de plus vérifié la cytotoxicité médiée par le complexe qui s'est avérée non spécifique au clone cellulaire exprimant le récepteur CD3 reconnu par l'Ac. Nous proposons deux mécanismes de liaison du complexe OKT3-AlPcS[indice inférieur 3]A[indice inférieur 1] au niveau des cellules."--Résumé abrégé par UMI.