The research presented herein describes the coupling of acoustic and heat release fluctuations in a perfectly-premixed swirl-stabilized combustor by analysis of simultaneous high-repetition-rate laser diagnostics data. Nine cases are studied, varying the thermal power and the equivalence ratio. Proper orthogonal decomposition (POD) of the velocity data shows that cases with higher amplitude thermoacoustic oscillations have flow fields containing helical vortex cores (HVC); these cases are further analysed to determine the driving mechanisms of the oscillations. Flow and flame statistics are compiled as a function of both the phase in the thermoacoustic cycle and a phase representing the azimuthal position of the HVC relative to the measurement plane. These data are used to spatially map the thermoacoustic energy transfer field, as described by the Rayleigh integral. It is found that periodic deformations of the HVC cause large-scale flame motions, resulting in regions of positive and negative energy transfer.

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<p> An experimental investigation of polymerisation of several monomers in wood was performed using free radical initiators such as benzoyl peroxide and 2-azo-bis-isobutyronitrile. The most promising comonomer system appeared to be styrene and acrylonitrile. As a result of copolymerisation of styrene and acrylonitrile in the cell cavities of wood, many improvements in physical properties of wood resulted. The improvement in physical properties of wood containing thermo-catalytically copolymerised styrene and acrylonitrile was found to be better than those of radiation initiated graft copolymerised wood. Thermo-catalytically produced wood polymer combinations showed as much improvement in physical properties as shown by those produced by radiation initiation without the use of swelling agents.</p> / Thesis / Master of Science (MSc)

No description available.

No description available.

Chickpea is a food legume crop grown in tropical, sub-tropical and temperate regions. World chickpea production is roughly three times that of lentils. Among pulse crops marketed as human food, world chickpea consumption is second only to dry beans. Turkey, Australia, Syria, Mexico, Argentina and Canada are major chickpea exporters. There are two types of chickpea, namely, the kabuli and the desi. The kabuli type is grown in temperate regions while the desi type chickpea is grown in the semi-arid tropics. Chickpea is valued for its nutritive seeds with high protein and starch content. They are eaten fresh as green vegetables, parched, fried, roasted, and boiled, as snack food, dessert and condiments. The seeds are ground and the flour can be used in soup, dhal and bread. Cooked chickpea is mostly preferred by consumers, especially the kabuli type. In this thesis, the heat and moisture transfer behavior of kabuli chickpea when subjected to cooking at different temperatures was investigated. The thermo-physical properties of chickpea were studied to develop a model to simulate the temperature distribution and moisture absorption in a chickpea seed when cooked in water. The thermo-physical properties determined experimentally were thermal conductivity, specific heat, moisture diffusivity, particle density and moisture content. Thermal diffusivity was calculated using the experimental values of thermal conductivity, specific heat and density. The water absorption in chickpea was determined when the seeds were soaked at different temperatures. It was observed that as the temperature of the soaking medium was increased, the rate of moisture absorption also increased. Soaking was done to enhance the gelatinization process during cooking. Cooking experiments were conducted for boiling temperatures ranging from 70 to 98°C for both soaked and unsoaked seeds. It resulted in the soaked seeds being cooked within 40-50 min, whereas the unsoaked seeds took around 250-300 min to cook. The amount of soluble solids lost during the cooking process is also reported which enables to predict the optimum soaking and cooking temperature. Using linear regression simple models for dependency of thermal conductivity, specific heat, thermal diffusivity and density on temperature and moisture content were developed. The rate of moisture transfer and the center temperature in the seed during cooking was determined experimentally and also simulated with the constant thermal properties found experimentally. The closeness of the simulated and experimental results was proved by appropriate statistical analysis. Based on the results obtained, it can be understood that soaking the chickpea seeds at temperatures ranging from 25 to 40°C for 8 h and cooking it at higher temperatures ranging from 90 to 100°C will improve the quality of the cooked seed with minimum mass loss. This optimum condition saves both energy and time.

Chickpea is a food legume crop grown in tropical, sub-tropical and temperate regions. World chickpea production is roughly three times that of lentils. Among pulse crops marketed as human food, world chickpea consumption is second only to dry beans. Turkey, Australia, Syria, Mexico, Argentina and Canada are major chickpea exporters. There are two types of chickpea, namely, the kabuli and the desi. The kabuli type is grown in temperate regions while the desi type chickpea is grown in the semi-arid tropics. Chickpea is valued for its nutritive seeds with high protein and starch content. They are eaten fresh as green vegetables, parched, fried, roasted, and boiled, as snack food, dessert and condiments. The seeds are ground and the flour can be used in soup, dhal and bread. Cooked chickpea is mostly preferred by consumers, especially the kabuli type. In this thesis, the heat and moisture transfer behavior of kabuli chickpea when subjected to cooking at different temperatures was investigated. The thermo-physical properties of chickpea were studied to develop a model to simulate the temperature distribution and moisture absorption in a chickpea seed when cooked in water. The thermo-physical properties determined experimentally were thermal conductivity, specific heat, moisture diffusivity, particle density and moisture content. Thermal diffusivity was calculated using the experimental values of thermal conductivity, specific heat and density. The water absorption in chickpea was determined when the seeds were soaked at different temperatures. It was observed that as the temperature of the soaking medium was increased, the rate of moisture absorption also increased. Soaking was done to enhance the gelatinization process during cooking. Cooking experiments were conducted for boiling temperatures ranging from 70 to 98°C for both soaked and unsoaked seeds. It resulted in the soaked seeds being cooked within 40-50 min, whereas the unsoaked seeds took around 250-300 min to cook. The amount of soluble solids lost during the cooking process is also reported which enables to predict the optimum soaking and cooking temperature. Using linear regression simple models for dependency of thermal conductivity, specific heat, thermal diffusivity and density on temperature and moisture content were developed. The rate of moisture transfer and the center temperature in the seed during cooking was determined experimentally and also simulated with the constant thermal properties found experimentally. The closeness of the simulated and experimental results was proved by appropriate statistical analysis. Based on the results obtained, it can be understood that soaking the chickpea seeds at temperatures ranging from 25 to 40°C for 8 h and cooking it at higher temperatures ranging from 90 to 100°C will improve the quality of the cooked seed with minimum mass loss. This optimum condition saves both energy and time.

Multilayer embedded passives (resistors, inductors, and capacitors) on a printed wiring board can help to meet high performance requirements at a low cost and at a smaller size. Such an integration of embedded passives has new challenges with respect to design, materials, manufacturing, thermal management and reliability. As the area of integral passives on printed circuit boards is relatively new, there is inadequate literature on the thermo-mechanical reliability of integral passives. Therefore, there is a compelling need to understand the thermo-mechanical reliability of integral passives through the development of physics-based models as well as through experiments, and this thesis aims to develop such an experimental and theoretical program to study the thermo-mechanical reliability of integral passives.. As integral passives are often composite layers with dissimilar material properties compared to the other layers in the integral substrate, it is essential to ensure that RLC characteristics of the embedded passives do not deteriorate with thermal cycling due to thermo-mechanical deformations. This thesis aims to study the changes in the passive characteristics due to the thermally-induced deformations. Embedded capacitors and inductors have been looked at specifically in this research. Multi-field physics-based models have been constructed to determine the change in electrical parameters after thermal cycling. The thermo-mechanical models assume direction-dependent material properties for the board substrate and interconnect copper layers and temperature-dependent properties for interlayer dielectric and passive layers. Using the deformed geometry, the electrical characteristics have been determined at low frequency. In parallel to the models, test vehicle substrates have been subjected to 1000 thermal cycles between -55??o 125??nd high humidity and temperature conditions at 85??5RH for 500 hours, and it has been observed that there are significant changes in the electrical parameters. The results obtained from the physics-based simulations have been validated against the measured electrical characteristics from the fabricated functional test boards that have been thermal cycled.

A recursive-iterative algorithm is developed for predicting nonlinear viscoelastic behaviors of isotropic materials that belong to the thermorheologically complex material (TCM). The algorithm is derived based on implicit stress integration solutions within a general displacement based FE structural analyses for small deformations and uncoupled thermo-mechanical problems. A previously developed recursive-iterative algorithm for a stress-dependent hereditary integral model which was developed by Haj-Ali and Muliana is modified to include time-temperature effects. The recursive formula allows bypassing the need to store entire strain histories at each Gaussian integration point. Two types of iterative procedures, which are fixed point and Newton-Raphson methods, are examined within the recursive algorithm. Furthermore, a consistent tangent stiffness matrix is formulated to accelerate convergence and avoid divergence. The efficiency and accuracy of the proposed algorithm are evaluated using available experimental data and several structural analyses. The performance of the proposed algorithm under multi-axial conditions is verified with analytical solutions of creep responses of a plate with a hole. Next, the recursive-iterative algorithm is used to predict the overall response of single lap-joint. Numerical simulations of time-dependent crack propagations of adhesive bonded joints are also presented. For this purpose, the recursive algorithm is implemented in cohesive elements. The numerical assessment of the TCM and thermorheologically simple material (TSM) behaviors has also been performed. The result showed that TCM are able to describe thermo-viscoelastic behavior under general loading histories, while TSM behaviors are limited to isothermal conditions. The proposed numerical algorithm can be easily used in a micromechanical model for predicting the overall composite responses. Examples are shown for solid spherical particle reinforced composites. Detailed unit-cell FE models of the composite systems are generated to verify the capability of the above micromechanical model for predicting the overall nonlinear viscoelastic behaviors.

Fuel cells are the direct energy conversion devices which convert the chemical energy of a fuel to electrical energy with much greater efficiency than conventional devices. Solid Oxide Fuel Cell (SOFC) is one of the various types of available fuel cells; wherein the major components are made of inherently brittle ceramics. Planar SOFC have the advantages of high power density and design flexibility over its counterpart tubular configuration. However, structural integrity, mechanical reliability, and durability are of great concern for commercial applications of these cells. The stress distribution in a cell is a function of geometry of fuel cell, temperature distribution, external mechanical loading and a mismatch of thermo-mechanical properties of the materials in contact. The mismatch of coefficient of thermal expansion and elastic moduli of the materials in direct contact results in the evolution of thermal stresses in the positive electrode/electrolyte/negative electrode (PEN) assembly during manufacturing and operating conditions (repeated start up and shut down steps) as well. It has long been realized and demonstrated that the durability and reliability of SOFCs is not only determined by the degradation in electrochemical performance but also by the ability of its component materials to withstand the thermal stresses. In the present work, an attempt has been made to evaluate the thermal stresses as a function of thermal and mechanical properties of the component materials assuming contribution from other factors such as thermal gradient, mechanical loading and in-service loading conditions is insignificant. Materials used in the present study include the state of art anode (Ni-YSZ), electrolyte(YSZ) and cathode materials(LM and LSM) of high temperature SOFC and also the ones being suggested for intermediate temperature SOFC Ni-SCZ as an anode, GDC and SCZ as electrolyte and LSCF as the cathode. Variation of thermo-mechanical properties namely coefficient of thermal expansion, and elastic and shear moduli were studied using thermo-mechanical analyzer and resonant ultrasound spectroscope respectively in 25-900°C temperature range. A non-linear variation in elastic and shear moduli- indicative of the structural changes in the studied temperature range was observed for most of the above mentioned materials. Coefficient of thermal expansion (CTE) was also found to increase non-linearly with temperature and sensitive to the phase transformations occurring in the materials. Above a certain temperature (high temperature region- above 600°C), a significant contribution from chemical expansion of the materials was also observed. In order to determine thermal stress distribution in the positive electrode, electrolyte, negative electrode (PEN) assembly, CTE and elastic and shear moduli of the component materials were incorporated in finite element analysis at temperature of concern. For the finite element analysis, anode supported configuration of PEN assembly (of 100mm x 100mm) was considered with 1mm thick anode, 10μm electrolyte and 30μm cathode. The results have indicated that cathode and anode layer adjacent to cathode/electrolyte and electrolyte/anode interface respectively are subjected to tensile stresses at the operating temperature of HT-SOFC (900°C) and IT-SOFC (600°C). However, the magnitude of stresses is much higher in the former case (500MPa tensile stress in cathode layer) when compared with the stress level in IT-SOFC (178MPa tensile stress in cathode layer). These high stresses might have been resulted from the higher CTE of cathode when compared with the adjacent electrolyte. However, it is worth mentioning here that in the present work, we have not considered any contribution from the residual stresses arising from fabrication and the stress relaxation from softening of the glass sealant.