Binderless fiberboard production from Cynara cardunculus and Vitis viniferaTwo lignocellulosic materials, Cynara cardunculus and Vitis vinifera, were pretreated and used to produce fiberboards without synthetic adhesives. The lignocellulosic materials were steam exploded through a thermo-mechanical vapor process in a batch reactor. After pretreatment the materials were dried, ground and pressed to produce the boards. The effects of pretreatment factors and pressing conditions on the chemical and physicomechanical properties of the fiberboards were evaluated and the conditions that optimize these properties were found. Response surface methodology based on a central composite design and multiple response optimization were used. The variables studied were: pretreatment temperature, pretreatment time, pressing temperature, pressing pressure, and pressing time. Binderless fiberboards produced from Cynara cardunculus stalks at the optimum conditions found fulfilled the European standards for boards of internal use. Nevertheless, binderless fiberboards produced from Vitis vinifera prunings at the optimum conditions found for this material did not completely met the European standards; modulus of rupture and internal bond values for these boards were lower than required minimums.Simultaneously, commercial Kraft lignin was reacted in an alkaline medium to enhance its adhesive properties. Chemical changes in reacted Kraft lignins that include ash content, Klason lignin, acid-soluble lignin and sugars were determined, as well as, structural characteristics of these lignins in terms of phenolic hydroxyl, aliphatic hydroxyl, methoxyl, carbonyl, Mw, Mn and polydispersity. The effects of reaction temperature and reaction time on lignin properties were studied using response surface methodology, and optimal reaction conditions were found.Two different types of Kraft lignin were used, alkali treated Kraft lignin and crude acid-washed Kraft lignin, as additives to enhance the physicomechanical properties of binderless fiberboards produced from Vitis vinifera to reach and overcome the European standards completely. At the end fiberboards produced with 20% of Vitis vinifera fibers replaced by crude acid-washed Kraft lignin were able to meet the European standards completely.This research work was an effort to reduce our dependency upon petroleum derivates, to diminish deforestation and to increase the use of renewable and biodegradable materials with the intention of preserving the environment and to encourage a sustainable development of our society. / Producción de Tableros de Fibras a partir de Cynara cardunculus y Vitis viniferaEn el presente estudio trozos Cynara cardunculus y Vitis vinifera fueron pretratados, y usados para producir tableros de fibras sin adhesivos sintéticos. Estos materiales lignocelulósicos se explotaron con vapor a través de un proceso termomecánico de vapor en un reactor por lotes. Después del pretratamiento el material fue secado, molido y prensado en caliente para producir los tableros. Se evaluaron los efectos de los factores del pretratamiento (temperatura de reacción y tiempo de reacción) y las condiciones de prensado (presión de prensado, temperatura y tiempo) sobre las propiedades químicas y físico-mecánicas de los tableros de fibras y se establecieron las condiciones que optimizan dichas propiedades. Las propiedades físico-mecánicas de los tableros de fibras que fueron estudiadas son: densidad, módulo de elasticidad (MOE), módulo de ruptura (MOR), enlace interno (IB), absorción de agua (WA) y hinchazón en hinchazón (TS) y las propiedades químicas estudiadas de la materia prima y el material pretratado fueron las siguientes: Cenizas, contenido de lignina Klason, contenido de celulosa y contenido de hemicelulosas. Se uso una metodología de superficie de respuesta basada en un diseño de experimentos del tipo central compuesto y una metodología de optimización de respuesta múltiple.Los tableros de fibras sin adhesivos sintéticos producidos a partir de tallos de Cynara cardunculus a las condiciones óptimas encontradas cumplieron con las normas europeas para los tableros de uso interno. Sin embargo, los tableros de fibras sin adhesivos sintéticos producidos a partir de podas de Vitis vinifera a las condiciones óptimas encontradas para este material no cumplieron totalmente las normas europeas; los valores del módulo de ruptura y del enlace interno para estos tableros fueron inferiores a los mínimos requeridos. Una lignina Kraft comercial fue sometida a reacción en un medio alcalino para mejorar sus propiedades adhesivas. Se determinaron los cambios químicos en las ligninas Kraft tratadas, las propiedades medidas fueron: contenido en cenizas, lignina Klason, lignina soluble en ácido y azúcares, también se determinaron las características estructurales de estas ligninas en términos de hidroxilos fenólicos, hidroxilos alifáticos, metóxilos, carbonilos, Mw, Mn y polidispersidad. Se estudiaron los efectos de la temperatura de reacción y el tiempo de reacción sobre las propiedades de la lignina con una metodología de superficie de respuesta, y se encontraron la condiciones óptimas de reacción.Se usaron dos tipos diferentes de lignina Kraft, lignina Kraft tratada en medio alcalino y lignina Kraft cruda lavada con ácido, como aditivos para mejorar las propiedades físico-mecánicas de los tableros de fibras sin adhesivos sintéticos producidos a partir de Vitis vinifera, para alcanzar y superar las normas europeas completamente. Al final los tableros de fibras producidos con una substitución del 20% de fibras de Vitis vinifera por lignina Kraft cruda lavada con ácido fueron capaces de satisfacer las normas europeas por completo.Este trabajo de investigación fue un esfuerzo para reducir nuestra dependencia de los derivados del petróleo, para disminuir la deforestación y para aumentar el uso de materiales renovables y biodegradables con la intención de preservar el medio ambiente y fomentar un desarrollo sostenible de nuestra sociedad.

En este trabajo se estudian los parámetros de obtención de tableros sin aporte de adhesivos, a partir de materiales lignocelulósicoscomo son la caña común (Arundodonax L.) y el bagazo de SaccharumofficinarumL. Los tableros propuestos aportan como ventaja el estar libres de emisiones de formaldehído y el no consumir recursos fósiles. Ambas propiedades son importantes en un mercado cada vez más exigente en aspectos medioambientales. En el caso del “ArundodonaxL” se ha partido de cañas silvestres de Tarragona. El bagazo de Saccharumofficinarum utilizado es el subproducto industrial de una destilería de la Isla de la Palma (Canarias). El material crudo ha sido pretratado realizando una “explosión de vapor” en un reactor “batch” a distintas condiciones de severidad. Este material explosionado se ha triturado y prensado en frío de dos formas (en seco y en húmedo). Posteriormente, los tableros prensados en frío y acondicionados a temperatura y HR constantes se han prensado en caliente a diferentes niveles de presión, temperatura y tiempo de prensado. En el proceso de producción a escala de laboratorio de los tableros, se han mejorado algunas de las fases seguidas como el prensado, introduciendo mallas de evacuación de vapor; y se han innovado otros, como la incorporación del prensado en frío y el tratamiento térmico final después de la conformación en caliente. Todo ello para mejorar la homogeneidad y obtener tableros de altas prestaciones mecánicas con estosmateriales. Se ha podido estudiar el efecto de los distintos factores que intervienen en la producción de tableros (Severidad del pretratamiento, temperatura de prensado, presión de prensado y tiempo de prensado), sobre las características físicas y mecánicas de estos tableros(Densidad, MOE, MOR, IB, TS y WA). Con ello se han obtenido las relaciones matemáticas que vinculan a estos factores de producción con las características físicas y mecánicas de los tableros. Puede ser muy importante para la industria el hecho de que los modelos ajustados definidos nos pueden permitir obtener tableros con características prefijadas. También se ha valorado la utilización de material integro explosionado y no lavado y, por tanto, sin ningún lixiviado ni residuo. Los tableros cumplen sobradamente los requerimientos de las norma EN para uso estructural, en todas las características físico-mecánicas estudiadas. Abreviaturas: HR Humedad relativa MOE Módulo de elasticidad en flexión o Módulo de Young MOR Módulo de rotura o Resistencia a la flexión IB Resistencia a la tracción perpendicular a las caras (Internal Bond) TS Hinchamiento WA Absorción de agua / This work studies the parameters for obtaining binderless fiberboards from lignocelullosic materials such as giant reed (Arundodonax L.) and sugar cane bagasse (Saccharumofficinarum L.) The suggested boards havethe advantage of being free from formaldehyde emissions and of not consuming fossil resources. Both properties are important in a market that is increasingly sensitivetowards environmental issues. Wild reeds from Tarragona were used as the base material to make Arundodonax Lfiberboards. The Saccharumoffinarumsugar cane bagasse was anindustrial byproduct obtained from a plantation on the island ofLa Palma in the Canary Islands (DestileríasAldea SL). The raw material was pre-treated by performing a “steam explosion” in a “batch” reactor. The exploded material was ground and cold-pressed in two ways (wet and dry). Subsequently, the cold-pressed boards, which had beenconditioned at a constant temperature and RH, were hot-pressed at different levels of pressure, temperature and press time. Some of the processes for producing boards on a laboratory-scale,such as pressing withsteam evacuation meshes, have been improved. Others processes were specifically developed in the laboratory, including the incorporation of cold-pressing and the final heat treatment after hot-forming. The aim of all this was to achieve high mechanical performance in boards made from these materials. Different factors involved in the production of the boards were studied (severity of pretreatment, pressing temperature, pressing pressure and pressing time) to determine how they affectthe physical and mechanical properties of these boards (density, MOE, MOR, IB, TS and WA). As a result, the mathematical relationships that link these production factors to the physical and mechanical properties of the boards were obtained. It is very significant for the industry that these adjusted models can produce boards with preset characteristics. The use of material that wascompletely exploded and unwashed and, therefore, without residue has also been studied. In terms of all the physical-mechanical characteristics studied,the boards fully comply with the requirements of the EN standards for structural use. Abbreviations RHRelativehumidity MOE Modulus of elasticity MOR Modulus of rupture IB Internal bond TS Thicknessswelling WA Water absorption

This degree project aims at developing a concept for how to use solar energy to pump up water. The target audience is people living in areas where the functioning of the electricity and water network is absent. In these areas, the hand-powered water pump is the most common technology. The degree project's goal is to find an economically viable alternative to the time consuming hand-powered water pumps. The power comes from solar energy. Studies have shown that 90% of the hand pumps that have been installed have broken down within the first three years. This is because of an incorrect basic design that severely shortens lifetime. How would a simple and robust design look like? An information seeking phase about the conditions and techniques that exist in these areas, were the basis for the requirements of the concept. Because of this the authors chose a concept similar to a simple steam engine. The pump uses vaporized water, by means of concentrating sunlight to pump up water. In total, 33 different concepts were created. The concepts were filtered in three stages that resulted in a final concept. The final concept contains a reflective dish that concentrates the sunlight to a receiver where the water evaporates. The built up pressure forces up water towards the surface from a tank located below the groundwater. The system is designed to supply 25 families with 2.5 cubic meters of water a day. The pump is working during the daily 8 hours of sunshine. The system will have an expected low efficiency <5.3% which is the theoretical maximum efficiency. Further development of the system requires a detailed analysis of the situation on the ground. Tests should be performed to examine how well the technology works and how sensitive the system is to disturbances.

This thesis covers the modelling of a Heat Recovery Steam Generator (HRSG) in a Combined Cycle Power Plant(CCPP). This kind of power plant has become more and more utilized because of its high efficiency and low emissions. The HRSG plays a central role in the generation of steam using the exhaust heat from the gas turbine. The purpose of the thesis was to develop efficient dynamic models for the physical components in the HRSG using the modelling and simulation software Dymola. The models are then to be used for simulations of a complete CCPP.The main application is to use the complete model to introduce various disturbances and study their consequences inthe different components in the CCPP by analyzing the simulation results. The thesis is a part of an ongoingdevelopment process for the dynamic simulation capabilities offered by the Solution department at SIT AB. First, there is a theoretical explanation of the CCPP components and control system included in the scope of this thesis. Then the development method is described and the top-down approach that was used is explained. The structure and equations used are reported for each of the developed models and a functional description is given. Inorder to ensure that the HRSG model would function in a complete CCPP model, adaptations were made and tuning was performed on the existing surrounding component models in the CCPP. Static verifications of the models are performed by comparison to Siemens in-house software for static calculations. Dynamic verification was partially done, but work remains to guarantee the validity in a wide operating range. As a result of this thesis efficient models for the drum boiler and its control system have been developed. An operational model of a complete CCPP has been built. This was done integrating the developed models during the work with this thesis together with adaptations of already developed models. Steady state for the CCPP model is achieved during simulation and various disturbances can then be introduced and studied. Simulation time for a typical test case is longer than the time limit that has been set, mainly because of the gas turbine model. When using linear functions to approximate the gas turbine start-up curves instead, the simulation finishes within the set simulation time limit of 5 minutes for a typical test case.

In Canada, coal-fired power plants are the largest anthropogenic point sources of atmospheric CO₂. The most promising near-term strategy for mitigating CO₂ emissions from these facilities is the post-combustion capture of CO₂ using MEA (monoethanolamine) with subsequent geologic sequestration. While MEA absorption of CO₂ from coal-derived flue gases on the scale proposed above is technologically feasible, MEA absorption is an energy intensive process and especially requires large quantities of low-pressure steam. It is the magnitude of the cost of providing this supplemental energy that is currently inhibiting the deployment of CO₂ capture with MEA absorption as means of combatting global warming. The steam cycle of a power plant ejects large quantities of low-quality heat to the surroundings. Traditionally, this waste has had no economic value. However, at different times and in different places, it has been recognized that the diversion of lower quality streams could be beneficial, for example, as an energy carrier for district heating systems. In a similar vein, using the waste heat from the power plant steam cycle to satisfy the heat requirements of a proposed CO₂ capture plant would reduce the required outlay for supplemental utilities; the economic barrier to MEA absorption could be removed. In this thesis, state-of-the-art process simulation tools are used to model coal combustion, steam cycle, and MEA absorption processes. These disparate models are then combined to create a model of a coal-fired power plant with integrated CO₂ capture. A sensitivity analysis on the integrated model is performed to ascertain the process variables which most strongly influence the CO₂ energy penalty. From the simulation results with this integrated model, it is clear that there is a substantial thermodynamic advantage to diverting low-pressure steam from the steam cycle for use in the CO₂ capture plant. During the course of the investigation, methodologies for using Aspen Plus® to predict column pressure profiles and for converging the MEA absorption process flowsheet were developed and are herein presented.

Solid oxide fuel cells (SOFCs) conventionally operate between 800 and 1000°C. The barriers for full-scale commercialization of SOFCs are the high cost and relatively poor long-term stability due to the high temperatures used in current state-of-the-art SOFCs. One solution is to decrease the operating temperature, e.g. to 550-750°C but this requires developing new electrolytes and electrode materials. Also, to increase efficiency and practicality, the anode should be able to internally reform hydrocarbon fuels especially methane because it is the most common hydrocarbon in natural gas. The overall goal of this research is to develop a coke-tolerant Ni1-x-yCuxMgyO-SDC anode for methane fuelled IT-SOFCs. The Ni-Cu-Mg-O-SDC anode has been chosen based on the premises that doped-ceria is suitable for intermediate operating temperatures (550-800°C), Ni is known as an active metal and good electronic conductor, Cu increases resistance to coking, MgO helps prevent agglomeration of Ni during reduction, and finally SDC improves oxide ion transport to the cell at this intermediate temperature range. In this work, these materials were characterized in three primary ways: material physical and chemical properties, methane steam reforming activity and electrochemical performance. Two different methods have been used to add Cu to Ni1-yMgyO: a one-step co-precipitation method and a two-step co-precipitation/impregnation method. For the first method, Ni1-x-yCuxMgyO was synthesized via co-precipitation of Ni, Mg and Cu. In the two-step method, Ni0.9Mg0.1O was first prepared by co-precipitation, followed by addition of copper to Ni0.9Mg0.1O by impregnation. However, co-precipitation of all metal in one step limits the sintering temperature of the anode in the cell fabrication due to the low boiling point of CuO. Therefore, co-precipitation of Cu is not a practical method and only Cu impregnation should be considered for practical SOFC applications. It was found that the addition of Mg (Ni0.9Mg0.1O) lowers the reducibility of NiO. Addition of Cu to Ni0.9Mg0.1O up to 5% shows similar reducibility as Ni0.9Mg0.1O. The reducibility of Ni1-x-yCuxMgyO becomes lower when the Cu content is increased to 10%. Nonetheless, all materials are fully reduced at 750ºC. The XRD patterns of pure NiO, Ni0.9Mg0.1O, and the Cu-containing material when Cu is less than 10 mol% are similar. The lower reducibility of Ni-Mg-O and Ni-Cu-Mg-O compared to NiO indicates that they form a solid solution with NiO as the matrix. Solid oxide fuel cells (SOFCs) conventionally operate between 800 and 1000°C. The barriers for full-scale commercialization of SOFCs are the high cost and relatively poor long-term stability due to the high temperatures used in current state-of-the-art SOFCs. One solution is to decrease the operating temperature, e.g. to 550-750°C but this requires developing new electrolytes and electrode materials. Also, to increase efficiency and practicality, the anode should be able to internally reform hydrocarbon fuels especially methane because it is the most common hydrocarbon in natural gas. The overall goal of this research is to develop a coke-tolerant Ni1-x-yCuxMgyO-SDC anode for methane fuelled IT-SOFCs. The Ni-Cu-Mg-O-SDC anode has been chosen based on the premises that doped-ceria is suitable for intermediate operating temperatures (550-800°C), Ni is known as an active metal and good electronic conductor, Cu increases resistance to coking, MgO helps prevent agglomeration of Ni during reduction, and finally SDC improves oxide ion transport to the cell at this intermediate temperature range. In this work, these materials were characterized in three primary ways: material physical and chemical properties, methane steam reforming activity and electrochemical performance. Two different methods have been used to add Cu to Ni1-yMgyO: a one-step co-precipitation method and a two-step co-precipitation/impregnation method. For the first method, Ni1-x-yCuxMgyO was synthesized via co-precipitation of Ni, Mg and Cu. In the two-step method, Ni0.9Mg0.1O was first prepared by co-precipitation, followed by addition of copper to Ni0.9Mg0.1O by impregnation. However, co-precipitation of all metal in one step limits the sintering temperature of the anode in the cell fabrication due to the low boiling point of CuO. Therefore, co-precipitation of Cu is not a practical method and only Cu impregnation should be considered for practical SOFC applications. It was found that the addition of Mg (Ni0.9Mg0.1O) lowers the reducibility of NiO. Addition of Cu to Ni0.9Mg0.1O up to 5% shows similar reducibility as Ni0.9Mg0.1O. The reducibility of Ni1-x-yCuxMgyO becomes lower when the Cu content is increased to 10%. Nonetheless, all materials are fully reduced at 750ºC. The XRD patterns of pure NiO, Ni0.9Mg0.1O, and the Cu-containing material when Cu is less than 10 mol% are similar. The lower reducibility of Ni-Mg-O and Ni-Cu-Mg-O compared to NiO indicates that they form a solid solution with NiO as the matrix. Addition of Mg also lowers the BET specific surface area from 11.5 m2/g for NiO:SDC to 10.4 m2/g for Ni0.9Mg0.1O. The surface area is further reduced when Cu is added; for example, at 10% Cu, the surface area is 8.2 m2/g. The activity of 50wt% Ni1-x-yCuxMgyO/50wt% SDC samples for methane steam reforming (SMR) and water-gas-shift reaction (WGS) was evaluated in a fully automated catalytic fixed-bed reactor where the exiting gases were analyzed online by a gas chromatograph (GC). The tests were performed at steam-to-carbon ratios (S/C) of 3, 2 and 1, and at temperatures of 750°C and 650°C for twenty hours. Higher methane conversions were obtained at the higher temperature and higher S/C ratio. Higher methane conversion are obtained using NiO:SDC and Ni0.9Mg0.1O:SDC than Ni-Cu-Mg-O. The conversion decreases with increasing Cu content. Over NiO:SDC and Ni0.9Mg0.1O:SDC the methane conversions are the same; for example 85% at 750°C for S/C of 3. At the same conditions, impregnation of 5%Cu and 10%Cu yields lower conversions: 62% and 48%, respectively. The activity for the WGS reaction was determined by mornitoring CO2/(CO+CO2) ratio. As expected because WGS is a moderately exothermic reaction, this ratio decreases when increasing the temperature. However, the CO2/(CO+CO2) ratio increases with higher S/C. The results indicate that adding Mg does not affect the WGS activity of NiO. The WGS activity of Ni0.9Mg0.1O:SDC is higher when Cu is added. The effect of additional Cu is more pronounced at 650ºC. At 750°C, changing the amount of Cu does not change the WGS activity because the WGS reaction rapidly reaches equilibrium at this high temperature. At 750°C for S/C of 1, carbon filaments were found in all samples. At 650ºC, different types of deposited carbon were observed: carbon fibers and thin graphite layers. Spent NiO:SDC had the longest carbon fibers. Addition of Mg significantly reduced the formation of carbon fibers. Impregnating 5% Cu on Ni0.9Mg0.1O:SDC did not change the type of deposited carbon. Monitoring the amount of deposited carbon on Ni0.9Mg0.1O:SDC, 3%Cu and 5%Cu impregnated on Ni0.9Mg0.1O:SDC for S/C of 0 at 750ºC showed that Cu addition deactivated methane cracking causing a reduction in the amount of carbon deposited. Electrochemical performance in the presence of dry and humidified hydrogen was determined at 600, 650, 700 and 750ºC. Electrolyte-supported cells constructed with four different anodes were tested using polarization curve and electrochemical impedance spectra. The four anodes were NiO:SDC, Ni0.9Mg0.1O:SDC, 3%Cu and 5%Cu on Ni0.9Mg0.1O:SDC. Adding Mg improved the maximum power density from 356 mW.cm-2 with NiO:SDC to 369 mW.cm-2 with Ni0.9Mg0.1O:SDC at 750ºC in dry hydrogen. Addition of Cu, on the other hand, lowered the maximum power density to 325 mW.cm-2 with 3%Cu impregnated and to 303 mW.cm-2 with 5% Cu impregnated. The cell with Ni0.9Mg0.1O:SDC was also tested under dry methane. To minimize methane cracking under this extreme condition, a current density of 0.10 A.cm-2 was always drawn when methane was present in the feed. The voltage decreased during the first hour from 0.8 to 0.5 V, then remained stable for 10 hours, and then started to drop again. Many small cracks were observed on the anode after completion of the electrochemical test, but there was no evidence of much carbon being deposited. In addition to dry methane, tests were also carried out, using the same material, with a H2O/CH4 mixture of 1/6 in order to generate a polarization curve at 750°C. Under these conditions, the maximum power density was 226 mW.cm-2. This is lower than the maximum power density obtained with humidified hydrogen, which was 362 mW.cm-2.

<p>This dissertation shows that the architecture of steam generators, steam turbines and heat exchangers for power plants can be predicted on the basis of the constructal law. According to constructal theory, the flow architecture emerges such that it provides progressively greater access to its currents. Each chapter shows how constructal theory guides the generation of designs in pursuit of higher performance. Chapter two shows the tube diameters, the number of riser tubes, the water circulation rate and the rate of steam production are determined by maximizing the heat transfer rate from hot gases to riser tubes and minimizing the global flow resistance under the fixed volume constraint. Chapter three shows how the optimal spacing between adjacent tubes, the number of tubes for the downcomer and the riser and the location of the flow reversal for the continuous steam generator are determined by the intersection of asymptotes method, and by minimizing the flow resistance under the fixed volume constraints. Chapter four shows that the mass inventory for steam turbines can be distributed between high pressure and low pressure turbines such that the global performance of the power plant is maximal under the total mass constraint. Chapter five presents the more general configuration of a two-stream heat exchanger with forced convection of the hot side and natural circulation on the cold side. Chapter six demonstrates that segmenting a tube with condensation on the outer surface leads to a smaller thermal resistance, and generates design criteria for the performance of multi-tube designs.</p> / Dissertation

The present work aimed at designing a thermally efficient microreactor system coupling methanol steam reforming with methanol combustion for autothermal hydrogen production. A preliminary study was performed by analyzing three prototype reactor configurations to identify the optimal radial distribution pattern upon enhancing the reactor self-insulation. The annular heat integration pattern of Architecture C showed superior performance in providing efficient heat retention to the system with a 50 - 150 degrees C decrease in maximum external-surface temperature. Detailed work was performed using Architecture C configuration to optimize the catalyst placement in the microreactor network, and optimize reforming and combustion flows, using no third coolant line. The optimized combustion and reforming catalyst configuration prevented the hot-spot migration from the reactor midpoint and enabled stable reactor operation at all process flowrates studied. Best results were obtained at high reforming flowrates (1800 sccm) with an increase in combustion flowrate (300 sccm) with the net H2 yield of 53% and thermal efficiency of >80% from methanol with minimal insulation to the heatintegrated microchannel network. The use of the third bank of channels for recuperative heat exchange by four different reactor configurations was explored to further enhance the reactor performance; the maximum overall hydrogen yield was increased to 58% by preheating the reforming stream in the outer 16 heat retention channels. An initial 3-D COMSOL model of the 25-channeled heat-exchanger microreactor was developed to predict the reactor hotspot shape, location, optimum process flowrates and substrate thermal conductivity. This study indicated that low thermal conductivity materials (e.g. ceramics, glass) provides enhanced efficiencies than high conductivity materials (e.g. silicon, stainless steel), by maintaining substantial thermal gradients in the system through minimization of axial heat conduction. Final summary of the study included the determination of system energy density; a gravimetric energy density of 169.34 Wh/kg and a volumetric energy density of 506.02 Wh/l were achieved from brass architectures for 10 hrs operation, which is higher than the energy density of Li-Ion batteries (120 Wh/kg and 350 Wh/l). Overall, this research successfully established the optimal process flowrates and reactor design to enhance the potential of a thermally-efficient heat-exchanger microchannel network for autothermal hydrogen production in portable applications.

The problem of the forced film condensation heat transfer of pure steam and steam-air mixture flowing downward a tier of horizontal cylinders is investigated numerically and experimentally. Liquid and vapor-air mixture boundary layers were solved by an implicit finite difference scheme. The effects of the free stream non-condensable gas (air) concentration, free stream velocity (Reynolds number), cylinder diameter, temperature difference and angle of inclination on the condensation heat transfer are analyzed. Inline and staggered tubes arrangements are considered. The mathematical model takes into account the effect of staggering of the cylinders and how condensation is affected at the lower cylinders when condensate does not fall on to the center line of the cylinders. An experimental setup was also manufactured and mounted at METU workshop. A set of experiments were conducted to observe the condensation heat transfer phenomenon and to verify the theoretical results. Condensation heat transfer results are available in ranges from (U&amp / #61605 / = 1 - 30 m/s) for free stream velocity, (m1,&amp / #61605 / = 0.01 -0.8) for free stream air mass fraction, (d = 12.7 -50.8 mm) for cylinder diameter and (T&amp / #61605 / -Tw =10-40 K) for temperature difference. Results show that / a remarked reduction in the vapor side heat transfer coefficient is noticed when very small amounts of air mass fractions present in the vapor. In addition, it decreases by increasing in the cylinder diameter and the temperature difference. On the other hand, it increases by increasing the free stream velocity (Reynolds number). Average heat transfer coefficient at the middle and the bottom cylinders increases by increasing the angle of inclination, whereas, no significant change is observed for that of the upper cylinder. Although some discrepancies are noticed, the present study results are inline and in a reasonable agreement with the theory and experiment in the literature. Down the bank, a rapid decrease in the vapor side heat transfer coefficient is noticed. It may be resulted from the combined effects of inundation, decrease in the vapor velocity and increase in the non-condensable gas (air) at the bottom cylinders in the bank. Differences between the present study results and the theoretical and the experimental data may be resulted from the errors in the numerical schemes used. These errors include truncation and round off errors, approximations in the numerical differentiation for interfacial fluxes at the vapor-liquid interface, constant properties assumption and approximations in the initial profiles. Mixing and re-circulation in the steam-air mixture at the lower tubes may be the other reasons for these deviations.

The world&rsquo / s being alerted to the global warming danger and the depletion of fossil fuel resources, has increased the importance of the clean and renewable hydrogen energy. Bioethanol has high potential to be used as a resource of hydrogen since it is a non-petroleum feedstock and it is able to produce hydrogen rich mixture by steam reforming reactions. Discovery of mesoporous MCM-41 type high surface area silicate-structured materials with narrow pore size distributions (20-100 &Aring / ) and high surface areas (up to 1500 m2/g) opened a new avenue in catalysis research. Catalytic activity of such mesoporous materials are enhanced by the incorporation of active metals or metal oxides into their structure. Nickel and copper are among the most active metals to be used in steam reforming of ethanol to produce hydrogen. In this study, copper and nickel incorporated MCM-41 type catalytic materials were tested in the steam reforming of ethanol. Two Ni-MCM-41 samples having different Ni/Si ratios were prepared by high temperature direct synthesis method and two Cu-MCM-41 samples having same Cu/Si ratios were synthesized by two different methods namely, high temperature direct synthesis method and impregnation method. The synthesized materials characterized by XRD, EDS, SEM, N2 physisorption and TPR techniques. XRD results showed that Ni-MCM-41 and Cu-MCM-41 catalysts had typical MCM-41 structure. The d100 and lattice parameter values of Ni-HT (I) (Ni-MCM-41 sample having 0.036 Ni/Si atomic ratio) was obtained as 3.96 and 4.57 nm., respectively. In addition Ni-HT (I) was found to have a surface area of 860.5 m2/g and 2.7 nm pore diameter. The d100 and lattice parameter values for a typical Cu-MCM-41 prepared by impregnation method having Cu/Si atomic ratio of 0.19 were obtained as 3.6 and 4.2 nm., respectively. This sample also has a 631 m2/g surface area and 2.5 nm pore diameter. Steam reforming of ethanol was investigated in the vapor phase by using Ni-MCM-41 and Cu-MCM-41 catalysts between 300&deg / C and 550&deg / C. Results proved that Ni incorporated MCM-41 type catalytic materials were highly active in hydrogen production by steam reforming of ethanol and actualized almost complete ethanol conversion for Ni-MCM-41 having Ni/Si atomic ratio of 0.15 over 500&deg / C . The side products obtained during reforming are methane and formaldehyde. Although the Cu-MCM-41 samples were not as active as Ni-MCM-41, it was observed that Cu-MCM-41 catalyst synthesized by the impregnation method showed an ethanol conversion of 0.83. However, the main product was ethylene with the copper incorporated catalysts. Effects of space time, the operating conditions (reaction temperature), metal/Si ratio of the catalyst and the preparation method on the product distributions were also investigated and best reaction conditions were searched.