Metal foams have many attractive properties such as light weight, low relative density, energy absorption capability etc. One of the main advantages of metal foam is that the foam inherits several properties of the parent metal, at the same time, at a fraction of the weight. Metal foams are basically of two types; closed pore and open pore. In the open pore configuration the highly porous structure with large surface to volume ratio is attractive in thermal applications such as heat exchangers, small scale refrigeration, diesel exhaust cooling and heat sink for electronics. Large surface area to volume ratio of the heat transfer area is an important parameter in design of heat exchangers. Application of open cell metal foam as a heat exchanger involves production of the metal foam, cutting/drilling the metal foam to required dimensions and attaching it to a substrate or duct. Foams are cut by various methods such as by using circular saw, band saw, abrasive sawing wire or electrical discharge machining. Cutting or drilling operations plastically deform the struts and affect the surface roughness of the struts and hence, the contact area between the foam and the substrate. The foam and the substrate are then joined to get the final product. Various techniques are adopted to join the foam and substrate that includes, press fit, welding, soldering, brazing and use of epoxy adhesives or thermal glue. These methods either deform the foam plastically or involve a bonding material which involves an additional step in manufacturing and is generally necessary to reduce the thermal resistance at the interface. Every secondary step involved in machining the foam and joining it to substrate/duct add to the energy, time and cost of the component. Significant amount of materials wastage occurs during the production and machining steps of the metal foam. Bonding material used for attaching foam to the substrate makes the recycling of the heat exchangers difficult. In the present research work the above issues were rectified by introducing a novel method of fabricating the heat exchanger in a single step. This can be done by producing open cell foam, bonded to the substrate in a single step to get the ready to use heat exchanger. The uniqueness of the method/ process is that it provides an advantage of manufacturing heat exchangers consisting of open cell aluminium foam both inside and outside the aluminium duct/substrate. Here open cell metal foam is metallurgic ally bonded to the aluminium duct without producing any distortion in the aluminium duct. The present method avoids the secondary cutting and joining operations, hence reducing material and energy wastage. This heat exchanger does not need a bonding material at the foam duct interface which makes the product completely recyclable without even having to separate the aluminium foam and, many-at-times, the copper substrate. Further, in the present process no hazardous material is involved in the fabrication process of the heat exchanger and all the materials used for the foam production can be recycled. Another unique advantage of this process is that the foam can also be cast inside and outside the tube in a single step. This helps increase the heat transfer area per unit volume inside the tube increasing the effectiveness significantly. First, an attempt was made to cast aluminium foam over a Cu substrate. Spheres made of Plaster of Paris (PoP) were used as space holders to create pores in the foam. First, a dough of PoP was prepared by mixing sufficient amount of water with the powder of PoP. Small pieces of PoP were taken from the dough and were rolled by hands to prepare spherical balls. Next, a casting setup was made where a die made of stainless steel was placed in a crucible whose bottom was filled with sand. A tube/duct made of copper was placed at the centre of the die and PoP balls were dropped around the duct. This setup was then placed in a furnace and was preheated to remove all the moisture from the PoP. Molten aluminium at around 700 °C was poured into the preheated die. After solidification, the die was opened and cast was allowed to cool in ambient air. PoP balls were removed by using a sharp needle and by dipping the casting in acetic acid. After removal of PoP from the cast, interconnected holes/cavities formed in the place of space holders/PoP balls, forming pores in the foam. There are some limitations of this method such as removal of PoP was tedious and needed chemicals that need to be discarded, PoP cannot be recycled and creates waste, small amount of moisture present in PoP balls can cause an explosion. The bonding between aluminium foam and Cu substrate obtained was not good, giving rise to thermal contact resistance. Due to the above limitations further implementation of this process using PoP was not explored further. There was a need of space holder material which can withstand the temperature of molten Al and also can be removed easily from the cast without any use of chemicals. Obtaining metallic bonding between foam and Cu substrate was difficult due to the corrosion layer formation at the interface of Al and Cu substrate due to preheating. If preheating was not carried out full penetration of the molten aluminium did not take place in the space available in between the spheres. Therefore, it was decided to cast Al foam over Al substrate. The main challenge and difficulty was to cast open cell Al foam inside and outside the tube/duct made of the same material (Al) without distorting the tube/duct as well as achieving consistent metallic bonding between the two. This has been successfully done by gravity casting method a single step manufactured and ready to use open cell Al foam heat exchanger were fabricated. A casting setup was prepared, which consisted of a commercially pure aluminium tube placed in the middle of a stainless steel split die. The gap between the tube and die was filled with the salt spheres. An uncommon and new approach was adopted to produce NaCl salt spheres. NaCl salt balls (spherical and ovoid) of different diameters were processed by casting route. The casting step of NaCl is necessary as the moisture present in NaCl can be completely removed during the melting of NaCl. NaCl was chosen as it had a melting point higher than aluminium. The casting setup was placed in a furnace and was preheated to various temperatures up to 550 °C. Commercially pure aluminium was melted separately in a crucible and was poured into the steel die at 700oC. The liquid metal flows through the die and fills the cavities between the salt balls. The die was opened immediately after solidification of molten Al and cast was allowed to cool in ambient air. The salt (NaCl), which was still solid, was dissolved in water to get the foam structure. With proper control of the preheat temperature and temperature of liquid aluminium no distortion of the aluminium duct was observed throughout the length of the heat exchanger. Consistent and complete fusion/ metallic bonding was observed at the interface of Al foam and Al substrate/duct. Several heat exchangers with different porosity and pore geometry with the aluminium foam cast outside the tube and both inside and outside of the tube were fabricated. The beauty of the designed method is that it is simple and cost effective and eliminates the major issue of thermal contact resistance since the foam and the duct are made of the same material and are bonded in the liquid state leaving no interface between the foam and the duct. Further, foam can also be cast inside the duct in the same step while casting the foam outside the tube, giving an integral heat exchanger which has higher heat transfer surface area to volume ratio inside and outside the duct. This is expected to further improve the efficiency and effectiveness of the heat exchanger An added advantage of this method is that the heat exchanger can be recycled easily in a single step re-melting route. Further, the heat exchanger does not use any hazardous material during manufacture that needs attention during recycling. After the production and fabrication of the heat exchangers, the thermal performance or effectiveness of the heat exchangers was assessed, to evaluate its usefulness and suitability for heat transfer application. An experimental test setup was fabricated in the laboratory to perform the heat transfer tests. The experimental test setup consists of the following major components;1) A test chamber whose function was to insulate the heat exchangers from the surroundings and to avoid any heat loss to the surroundings, 2) An air blower used to supply cold fluid (air) to the test chamber, 3) A constant temperature bath was used to supply the hot fluid, which was water in this case, in the duct of the heat exchanger, 4) A rotameter was used to measure the volumetric flow rate of the cold fluid and 5) A pressure gauge having the pressure measurement range between 1 mbar to 160 mbar to measure the pressure drop across the test chamber. K-type chromel – alumel thermocouples having temperature measurement range between -270 °C to 1,260 °C were used to measure the temperature of hot and cold fluids during the experiments. By aid of the data logger system and computer, temperature readings were recorded during the tests and were used further for the heat transfer calculations. For testing the aluminium foam heat exchangers was placed in the insulated test chamber. Hot water was supplied inside the duct of heat exchanger whereas air at room temperature was supplied around the foams at varying flow rates during the tests. During the tests, temperature readings were taken at steady state condition. NTU-Effectiveness method was used to evaluate the thermal performance of heat exchangers. Overall results obtained by this experimental study are as follows • As the inlet temperature difference between hot and the cold fluids increases the heat transfer rate and the effectiveness of the heat exchangers also increases. • At a constant flow rate of hot fluid, heat exchangers exhibits significantly better thermal performance at lower flow rate of cold fluid compared to higher flow rate. As the flow rate of cold fluid increases, the velocity of the fluid increases and consequently, reduces the optimum interaction time between hot and the cold fluids required for the efficient heat transfer. • At a constant and low flow rate of cold fluid the effectiveness of the heat exchanger increases as the porosity of the foam increases. But when the flow rate of cold fluid was increased further after a certain limit, the effectiveness value of the heat exchanger decreases. • Heat exchanger consisting of foam of higher porosity exhibits higher effective. • Heat exchanger having foam inside and outside of the duct/tube exhibits significantly higher effectiveness compared to Al duct, Cu duct and other heat exchanger tested. • At a higher flow rate of the cold fluid, the heat exchangers consisting of foams of higher porosity, experience more drop in effectiveness compared to the heat exchanger having foams of low porosity. • Pressure drop across the length of the foam/fin increases as the volumetric flow rate of the cold fluid (m3/s) increases. • Surface area per unit volume and effectiveness values for bare Al tube is very low compared to Al foam heat exchangers resulting in the bare Al tube exhibiting much lower effectiveness compared to heat exchanger made of Al foam. • For a certain flow rate of fluids, the effectiveness of the heat exchanger increases up to a certain thickness of the Al foam. • Regardless of the thickness of the foam, the effectiveness of the heat exchangers is low at higher flow rate of cold fluid compared to lower flow rate. • These foam based heat exchanger had a much higher effectiveness when compared to that of other heat exchangers, data of which were got from literature. The present experimental study concludes that fuse bonding open cell aluminium foam over an Al duct or Al substrate can improve the thermal performance of the heat exchanger significantly. The thesis includes five chapters. Chapter 1 gives a detailed introduction about the metal foam, heat exchangers, thermal contact resistance and its effect on the heat transfer rate has been explained. This chapter also includes the overall aim and motivation for the research work. Chapter 2 covers the literature available on production methods of metal foam and its limitations has been listed out. And conventional methods of manufacturing open cell metal foam heat exchangers and its disadvantages have been explained in detailed. Chapter 3 covers in detail the novel method of production and fabrication of open cell metal foam heat exchangers. Chapter 4 includes an experimental study, where thermal performance of heat exchangers has been assessed through heat transfer experiments. Chapter 5 is the conclusions and future works.

The larvae of coastal species interact with nearshore currents that are complex and can alter dispersal. I investigated two sites in southern Oregon with different nearshore hydrodynamics: the first site, Sunset Bay, is a small cove with a topographic front that extends across the mouth during upwelling-favorable winds. Using holey sock drogues at 1.5 m and 5.5 m depths and surface drifters at 10 cm depth, I found that, when the front was present, water at 1.5 m was retained within the bay whereas water was exchanged across the front at a depth of 5.5 m. Surface drifters indicated a surface convergence. Surface plankton tows on either side and within the frontal convergence (a shore-parallel foam line) found significantly higher concentrations of barnacle cyprids, crab megalopae and zoea, polychaete larvae, platyhelminthes juveniles, isopods, amphipods, harpacticoid copepods, and fish eggs. Crustacean nauplii (barnacle, euphausiid, and copepod) and calanoid copepods were not concentrated in the convergence, and when the front and foam line were absent, no taxa were concentrated. Plankton tows taken within the foam line as it dissipated shoreward during a wind-reversal event found that concentrations of cyprids, megalopae, and gastropod veligers remained high as the foam line moved, suggesting that it acts as a moving convergence propagating competent larvae shoreward. I measured settlement of two taxa at Sunset Bay and Shore Acres, an open-coast site <2 km away. Barnacle settlement measured every other day from June-September 2013 was significantly cross-correlated with the maximum daily tidal height at lags of -2 days at Sunset Bay and +2 and +4 days at Shore Acres. Settlement was also significantly negatively cross-correlated with wave height at a lag of -4 days at Sunset Bay. Coralline algae settlement measured during eight 48-hr periods in July-August 2013 was significantly negatively correlated with wave height (n = 8, R2 = 0.76, P = 0.0049) at Shore Acres but not at Sunset Bay. Despite the close proximity of the Sunset Bay and Shore Acres sites, settlement patterns differed between taxa, suggesting that differences in nearshore hydrodynamics might affect the supply of water and larvae to shore. This dissertation includes unpublished co-authored material.

abstract: Due to increasing integration of renewable resources in the power grid, an efficient high power transmission system is needed in the near future to transfer energy from remote locations to the load centers. Gas Insulated Transmission Line (GIL) is a specialized high power transmission system, designed by Siemens, for applications requiring direct burial or vertical installation of the transmission line. GIL uses SF6 as an insulating medium. Due to unavoidable gas leakages and high global warming potential of SF6, there is a need to replace this insulating gas by some other possible alternative. Insulating foam materials are characterized by excellent dielectric properties as well as their reduced weight. These materials can find their application in GIL as high voltage insulators. Syntactic foam is a polymer based insulating foam. It consists of a large number of microspheres embedded in a polymer matrix. The work in this thesis deals with the development of the selection proce-dure for an insulating foam for its application in GIL. All the steps in the process are demonstrated considering syntactic foam as an insulator. As the first step of the procedure, a small representative model of the insulating foam is built in COMSOL Multiphysics software with the help of AutoCAD and Excel VBA to analyze electric field distribution for the application of GIL. The effect of the presence of metal particles on the electric field distribution is also observed. The AC voltage withstand test is performed on the insulating foam samples according to the IEEE standards. The effect of the insulating foam on electrical parameters as well as transmission characteristics of the line is analyzed as the last part of the thesis. The results from all the simulations and AC voltage withstand test are ob-served to predict the suitability of the syntactic foam as an insulator in GIL. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2014

No description available.

A laboratory investigation into foam separation processes, as applied to kraft pulping and bleaching effluents is described. Two methods, foam fractionation and ion flotation were tested in the laboratory. The procedures developed concentrated primarily on the removal of effluent colour because this property lent itself most readily to the available analytical methods, and because effluent colour removal presents one of the greatest waste water treatment problems facing the industry today. The foam fractionation technique was not successful. Substantial colour removals were obtained, but it was subsequently shown that the mechanism of removal was really an ion flotation. Positive results were obtained with the use of the ion flotation process for removal of effluent colour. At optimum conditions, the recovery of flotable material and the corresponding removal of effluent colour were in excess of 95 per cent. Variation of surfactant dosage showed that below a critical level no colour was removed. As concentrations increased above this value the amount of colour removed increased rapidly, reaching a high removal level beyond which increases in surfactant concentration were of little value. The rate of flotation recovery was found to be significantly affected by the air sparge rate and the sparger pore size, both parameters which would determine the area available for adsorption. The pH of the flotation cell solution had a marked effect on the system. Optimum pH was clearly defined as 5.1. Removal of material other than just the chromophoric fraction was apparent. Biological oxygen demand data, while not extensive, demonstrate a significant reduction in the bio-degradable portion of the effluent. The possible future development of the process into a viable candidate for industrial application is discussed. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Les mousses liquides sont des dispersions des bulles dans l'eau et elles sont largement utilisées dans un grand nombre de procédés technologiques et d’applications commerciales. Dans ma thèse, je me concentre sur les différents problèmes concernant les propriétés des mousses aqueuses et en particulier les écoulements gravitationnels dans les mousses.Les mousses contiennent une grande quantité d'interfaces couvertes par des molécules amphiphiles, et l'échange des tensioactifs entre l'interface et la phase volumique joue un rôle important pour la génération et la stabilité des mousses. Donc, mon premier projet a été d'étudier la dynamique d'adsorption de systèmes modèles aux interfaces air/eau. Les résultats obtenus nous ont aidés à comprendre comment l'adsorption lente des tensioactifs lors de la génération de la mousse peut influencer la mobilité des interfaces et changer le drainage de la mousse. Pour étudier les différents aspects de la physique de la mousse à l'échelle des bulles, des mousses pseudo-bidimensionnelles (des monocouches des bulles serrées entre deux plaques) sont largement utilisées. Dans ma thèse un modèle pour décrire la géométrie d'une mousse pseudo-bidimensionnelle a été introduit, cette description a été utilisée pour modéliser les conductivités électriques et hydrauliques de ces mousses. Dans certaines applications (par exemple, dans les industries du papier et de la peinture) la formation de la mousse peut causer de graves problèmes et des agents antimoussants appropriés sont utilisés. Dans ma thèse l'influence de la gravité sur l'efficacité antimoussante des gouttes d'huile de silicone a été étudiée expérimentalement en utilisant des vols paraboliques. Les résultats montrent que les particules antimoussantes ont besoin de la gravité pour être transportées d'une manière efficace, et la microgravité rend les antimousses très efficaces pratiquement inutiles. Etant initialement motivé par le transport des particules dans les mousses, j'ai également examiné la sédimentation des particules solides dans les capillaires de verre verticaux et inclinés. / Liquid foams are dispersions of bubbles in water and they are widely used in a large number of technical processes and commercial applications. In the present thesis I focus on different problems concerning properties of aqueous foams and especially gravity-driven flows in foams. Foams contain a large quantity of interfaces covered by surfactant molecules and the surfactant exchange between bulk and interface plays a crucial role for foam generation and stability. So my first project was to study the adsorption dynamics of model surfactant systems at air/water interfaces. The obtained results helped us to understand how the slow surfactant adsorption during foam generation can influence the mobility of interfaces and change foam drainage. To study different aspects of foam physics at the bubble scale simplified quasi-2D foams (monolayers of bubbles squeezed between two plates) are widely used. In this thesis a model to describe the geometry of a quasi-2D foam was introduced, this description was used to model the electrical and flow conductivities of such foams. In some applications (for example, in the paper and paint industries) foam formation can cause serious problems and suitable antifoaming agents need to be used. In my thesis the influence of gravity on the antifoaming efficiency of silicone oil droplets has been experimentally studied using parabolic flights. The results show that antifoam particles need gravity to be efficiently transported, and microgravity can render highly efficient antifoam practically useless. Being initially motivated by particle transport in foams, I have also looked at the sedimentation of solid particles in vertical and inclined glass capillaries.

This study examined several structure-property features of flexible polyurethane foams that are important aspects of foam production. AFM and WAXS were used to demonstrate the existence, for the first time in typical polyurethane foam systems, of lamellae-like polyurea structures ca. 0.2 mm long and ca 5-10 nm across. Aggregations of these lamellae-like hard domains may be the polyurea balls typically observed via TEM. Diethanolamine, a widely used cross-linking agent in molded foams, was shown to disrupt ordering in the polyurea hard domains and alter the interconnectivity of hard domains by preventing the formation of lamellae-like structures. These changes were shown to lead to softening of the foam. Copolymer polyol is frequently applied as reinforcing filler in foams. It was found that a common method of adding this component alters the hard segment/soft segment (HS/SS) ratio, thus increasing the load bearing capacity of the foam. It was observed in this report that at constant HS/SS ratio, the copolymer polyol only increased load bearing under humid conditions. It was also shown that the collapse of the cellular structure of a foam prior to the point of urea precipitation alters the aggregation behavior of the hard domains and alters solid-state properties. Surfactant is thus suggested to play a secondary role in the development of the hard domains by maintaining the cellular structure in the foam as the phase separation occurs and at least until the polyurethane foam has more fully organized hard segment domains. It was found that cure temperature could be manipulated to predictably change interdomain spacings and hydrogen bond development in the polymer. Curing above 100°C was found to lower hard segment content for plaques of the same formulation possibly as a result of water and isocyanate vaporization. Apart from polyurethane materials, structure-property relationships were examined in cast blends based on poly(tetrafluoroethylene) (PTFE) and the terpolymer poly(tetrafluoroethylene-co-vinylidene fluoride-co-hexafluoropropylene) (FKM). This revealed that tensile and dynamic moduli could be predictably altered by controlling the degree of FKM cross-linking or by varying PTFE content in the film. Inducing PTFE fibrillation was found to yield higher modulus films without increasing PTFE content. / Ph. D.

No description available.

No description available.

This project is about automating foam quality control. Its purpose is to construct an automated quality-control station that will characterise foam in line with a production line that non-technical persons can efficiently operate. Foam passes through the station on a purpose-built conveyor. A robot then moves a microscope over the foam to capture detailed close-up images. The characterisation is done in software by examining the foam’s pores and measuring it against a set of tweakable parameters. There were some problems in focusing the microscope, but testing resolved the focusing to be non-essential. A database is used with the quality control station to store and sort test data efficiently. The overall quality control station is a success and can characterise foam according to the project’s predefined goals.