Martensitic steels have become very important engineering materials in modern society. Crucial parts of everyday products are made of martensitic steels, from surgical needles and razor blades to car components and large-scale excavators. Martensite, which results from a rapid diffusionless phase transformation, has a complex nature that is challenging to characterize and to classify. Moreover the possibilities for modeling of this phase transformation have been limited, since its thermodynamics and kinetics are only reasonably well understood. However, the recent development of characterization capabilities and computational techniques, such as CALPHAD, and its applicability to ferrous martensite has not been fully explored yet. In the present work, a thermodynamic method for predicting the martensite start temperature (Ms) of commercial steels is developed. It is based mainly on information on Ms from binary Fe-X systems obtained from experiments using very rapid cooling, and Ms values for lath and plate martensite are treated separately. Comparison with the experimental Ms of several sets of commercial steels indicates that the predictive ability is comparable to models based on experimental information of Ms from commercial steels. A major part of the present work is dedicated to the effect of carbon content on the morphological transition from lath- to plate martensite in steels. A range of metallographic techniques were employed: (1) Optical microscopy to study the apparent morphology; (2) Transmission electron microscopy to study high-carbon plate martensite; (3) Electron backscattered diffraction to study the variant pairing tendency of martensite. The results indicate that a good understanding of the martensitic microstructure can be achieved by combining qualitative metallography with quantitative analysis, such as variant pairing analysis. This type of characterization methodology could easily be extended to any alloying system and may thus facilitate martensite characterization in general. Finally, a minor part addresses inverse bainite, which may form in high-carbon alloys. Its coupling to regular bainite is discussed on the basis of symmetry in the Fe-C phase diagram. / <p>QC 20120824</p> / Hero-m

This study deals with the thermodynamic analysis of a molten carbonate fuel cell (MCFC) hybrid system to determine its efficiencies, irreversibilities and performance.The analysis includes a performance investigation of a typical molten carbonate fuel cell stack, an industrial MCFC hybrid system, and an MCFC hybrid system deployed by Enbridge. A parametric study is performed to examine the effects of varying operating conditions on the performance of the system. Furthermore, thermodynamic irreversibilities in each component are determined and an optimization of the fuel cell is conducted. Finally, a simplified and novel method is used for the cost analysis of the Enbridge MCFC hybrid system.An exergy analysis of the hybrid MCFC systems demonstrates that overall efficiencies of up to 60 % are achievable. The maximum exergy destruction was found in components in which chemical reactions occur. In addition, the turboexpander is one of the major contributors to the overall exergy destruction of the system. The cost analysis of the Enbridge system illustrates that by merging the importance of “green” energy and rising costs of carbon offsets, this new technology could be a promising solution and substitute for future energy supply. / UOIT

This dissertation aims to study the mid-level clouds using satellite observations. It consists of two major parts: characteristics (including cloud top/base heights, cloud top pressure and temperature, and cloud thickness) and thermodynamic phase of mid-level clouds. Each part devotes to a particular issue of significant importance for satellite-based remote sensing of mid-level clouds. The first part of this dissertation focuses on the impacts of three definitions of the mid-level clouds based on cloud top pressure, cloud top height, and cloud base height on mid-level cloud characteristics. The impacts of multi-layer clouds on satellite-based global statistics of clouds at different levels, particularly for mid- level clouds, are demonstrated. Mid-level clouds are found to occur more frequently than underlying upper-level clouds. Comparisons of cloud amounts between a merged CALIPSO, CloudSat, CERES, and MODIS (CCCM) dataset and International Satellite Cloud Climatology Project (ISCCP) climatology are made between July 2006 and December 2009. Midlevel cloud characteristics are shown to be sensitive to perturbations in midlevel boundary pressures and heights. The second part focuses on the thermodynamic phase of mid-level clouds. A new algorithm to detect cloud phase using Atmospheric Infrared Sounder (AIRS) high spectral measurements is introduced. The AIRS phase algorithm is based on the newly developed High-spectral-resolution cloudy-sky Radiative Transfer Model (HRTM). The AIRS phase algorithm is evaluated using the CALIPSO cloud phase products for single-layer, heterogeneous, and multi-layer scenes. The AIRS phase algorithm has excellent performance (>90%) in detecting ice clouds compared to the CALIPSO ice clouds. It is capable of detecting optically thin ice clouds in tropics and clouds in the mid-temperature range. Thermodynamic phase of mid-level clouds are investigated using the spatially collocated AIRS phase and CALIPSO phase products between December 2007 and November 2008. Overall, the statistics show that ice, liquid water, and mixed-phase of the mid-level clouds are approximately 20%, 40%, and 40%, globally.

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Thesis (Ph. D.)--Institute of Paper Chemistry, 1960. / Includes bibliographical references (p. 100-102).

Among the major deterioration problems a gas turbine encountered while in operation is compressor blade fouling. This is the accumulation and adhesion of dirt and sediment on the compressor blade which contributes between 70 to 85% of gas turbine performance loss. Fouling reduces turbine air mass flow capacity, compressor pressure ratio and overall gas turbine efficiency. In most cases, its effect does not manifest immediately in gas turbine power output and efficiency since they are not measured directly. However, it is apparent on the gradual increase in Turbine Entry temperature (TET) and Exhaust Gas Temperature (EGT). More fuel is burnt in the combustion chamber to maintain turbine power output which leads to high combustion flame temperature and thus reduces creep life of hot components. This research seeks to analyse the technical and economic consequences of compressor fouling in overall gas turbine performance. The work begins with simulation of TS3000 engine and examination of its design and off design performance. Subsequently, medium size gas turbine engine was modelled, simulated and its performance at different condition was examined to validate the outcome of field data analysis. Three months field operating data of Hitachi H-25 gas turbine generator used for power generation at bonny oil and gas terminal in Nigeria was collected and corrected to international standard ambient condition, using thermodynamic calculations. These data were analysed to determine the effect of fouling on the engine fuel consumption, power output in order to determine the plant profitability. The above analysis gives an estimation of fuel cost saving benefit of $41,000 over the period of one year plant operation due to regular two weekly compressor online water wash which is a good indication of the engine efficiency.

The development of a control-oriented dynamic relative humidity model for a polymer electrolyte membrane (PEM) fuel cell stack is presented. This model is integrated with a first law based thermal model, which tracks energy flow within four defined control volumes in the fuel cell; the cathode channel, anode channel, coolant channel, and fuel cell stack body. Energy and mass conservation equations are developed for each control volume. On top of mass conservation, electro-drag and osmosis models were also implemented within the model to account for the major modes of vapor transfer through the membrane between the anode and cathode. Requisite alterations to the thermal model as well as mass flow rate calculations are also discussed. Initially, the model utilized a single lumped control volume for the calculation of all values each channel (anode and cathode). This lumped value method is computationally inexpensive, and makes the model optimal for control design. However, investigation of the mass-based Biot number showed the need for greater granularity along the length of the channels to properly capture the relative humidity dynamics. In order to improve the resolution of the model, while still minimizing the computation expense, the model was subdivided into a series of lumped value models. The cathode channel was the point of focus as it is the major concern from a controls perspective. This method captures the proper trends found in far more complex CFD models, while still maintaining a quick calculation time. Different levels are subdivision (3 and 6 submodels) are investigated, and the differences discussed. Particularly, temperature range, relative humidity range, the effect on the modeled voltage, and calculation time are compared. This control-oriented model is low order and based on lumped parameters, which makes the computational expense low. Formulation of this model enables the development of control algorithms to achieve optimal thermal and water management. / text

Vapor pressure data are vital to understanding impacts that substances, specifically pesticides, may exert on the environment. They enter into atmospheric deposition models for such chemicals which determine the fate and transport of these species in the environment. At normal application temperatures (i.e. room temperature) the vapor pressures of many of these chemicals are too low to be determined by conventional means. An isothermal Knudsen effusion technique was designed and developed in our laboratory for such measurements. The effusion mass as a function of time is measured in our technique using a thickness shear mode (TSM) acoustic wave sensor, which allows for extremely high (few nanograms) sensitivity. This sensitivity allows for much more rapid determination of low vapor pressures (10-1 to 10-5 Pa) than is possible by other Knudsen effusion techniques. Basing the effusion mass measurement on the TSM sensor as in our apparatus eliminates the typically seen dependence on vibration in conventional microbalance-based effusion techniques. Full design details of our apparatus and specifically the Knudsen cell, based on original equations derived by Knudsen, and many corrections that have been noted in the literature for cell and effusion-hole dimensions, are presented. The accuracy of our methodwas tested by a comparison of published vapor pressure data to vapor pressure data acquired in our laboratory with measurements on naphthalene and catechol.

Niobium (Nb) is a fascinating element, that when it is in a solid state has remarkable properties. This is believed to be a result of its electronic configuration that has partially filled 4d and 5s sub-shells. Nb has a melting temperature of 2750 K, a high strength at high temperature, and a good wear resistance. Because of these properties, Nb is used as material for components of rockets and jet engines, and for strengthening steel. In the phonon dispersion relations, Kohn anomalies are experimentally observed to weaken with increased temperature, which is related to the superconducting properties of Nb. I include anharmonicity when I calculate the thermodynamic properties of Nb and relate this to the electronic structure. In this thesis I show that anharmonicity can not be neglected when considering thermodynamic properties of Nb. I observe broadening in the electronic band structure with increasing temperature, correlated with the gradual weakening of the Kohn anomalies in the phonon dispersion relations. Kohn anomaly in the phonon dispersion relation can be observed at 300 K and is completely absent at 1200 K. The observation of the Kohn anomaly's disappearance in the calculations is of great importance because it cannot be repeated by approaches that do not include anharmonic effects, meaning that properties that are directly related to phonon dispersion, like elastic constants, can be calculated more accurately with this approach.

There have been many studies in the energy field to achieve different goals such as energy security, energy independence and production of cheap energy. The consensus of the general population is that renewable energy sources can be used on a short-term basis to compensate for the energy requirement of the world. However, the prediction is that fossil fuels will be used to provide the majority of energy requirements in the world at least on a short-term basis. Coal is one of the major fossil fuels and will be used for a long time because there are large coal reservoirs in the world and many products such as hydrogen, ammonia, and diesel can be produced using coal. In the present study, the performance of a clean energy system that combines the coal gasification and alkaline water electrolyzer concepts to produce hydrogen is evaluated through thermodynamic modeling and simulations. A parametric study is conducted to determine the effect of water ratio in coal slurry, gasifier temperature, effectiveness of carbon dioxide removal, and hydrogen recovery efficiency of the pressure swing adsorption unit on the system hydrogen production. In addition, the effects of different types of coals on the hydrogen production are estimated. The exergy efficiency and exergy destruction in each system component are also evaluated. Although this system produces hydrogen from coal, the greenhouse gases emitted from this system are fairly low.