Cold spray is a unique additive manufacturing process, where a large number of ductile metal micro particles are deposited to create new surface coatings or free-standing structures. Metallic particles are accelerated through a gas stream, reaching velocities of over 1 km/s. Accelerated particles experience a high-strain-rate microscopic ballistic collisions against a target substrate. Large amounts of kinetic energy results in extreme plastic deformation of the particles and substrate. Though the cold spray process has been in use for decades, the extreme material science behind the deformation of particles has not been well understood due to experimental difficulties arising from the succinct spatial (10 μm) and temporal scales (10 ns). In this study, using a recently developed micro-ballistic method, the advanced laser induced projectile impact test (α-LIPIT), the dynamic behavior of micro-particles during the collision is precisely defined. We observe single aluminum 6061 alloy particles, approximately 20μm in diameter, impact and rebound off of a rigid target surface over a broad range of impact speeds, temperatures, and substrate oxide film thicknesses. Through observation of the collisions, we extract characteristic information of the dynamic response of particles as well as the relationship with various parameters (e.g. surrounding temperature, particle diameter, oxide thickness, and impact velocity). By impacting a polished aluminum 6061 alloy substrate we are able to mimic the collision events that occur during cold spray deposition. The connection between the temperature increase and the oxide thickness plays a role in theorizing the cause of unexpected phenomena, such as increased rebound energies at higher temperatures. Highly-controlled single particle impacts results, are provided to calibrate and improve computational simulations as well. This, in turn, can provide insight into the underlying material science behind the cold spray process.

GSHP systems are common in Sweden but there are few evaluations quantifying the performance of the systems and highlighting problem that occurs during operations. The research project Annex 52 Long-term performance measurement of GSHP systems serving commercial, institutional and multifamily building part of IEA HPT TCP proves the need to systematically be able to evaluate GSHP systems. This thesis aims to expand the knowledge of how to evaluate GSHP systems and provide case studies for Annex 52. Three residential ground source heating systems used for heating has been evaluated and analyzed in this study. The evaluation has consisted of three parts. The first part analyzes the operation and stability of the GSHP systems. The second part consist of a detailed study of the performance of the GSHP systems. The seasonal performance factor has been calculated for different system boundaries based on the work done by SEPEMO. In addition, a method on how to evaluate the efficiency of the heat pumps based on the two temperature levels, source side temperature and the heat sink temperature, that the heat pump is operating at throughout a year has been developed within this thesis. This has included a method on how to normalize the temperatures based on the operation of the heat pump in order to quantify one temperature for each the two temperature levels. The third part consist of a comparison of the mean secondary fluid temperature between the calculated temperature using the software EED and the measured temperatures. This includes a comparison evaluation and sensitivity analysis on input parameters during the design of the borehole heat exchanger fields. This study has expanded the available reference cases of GSHP systems in Sweden. It also can be used as a guideline for those who will evaluate future GSHP systems. Designers of GSHP system will also benefit from the recommendations listed in this thesis regarding instrumentation and possible problems that may occur. The results show that the evaluation successfully managed to quantify the performance and operational issues that have occurred for each system. The method developed in this study was able to quantify the operation of the different systems based on the temperature levels and can be used for future GSHP evaluations of similar system type. / Bergvärmesystem är vanligt förekommande i Sverige men trots detta finns det få studier där prestandan har utvärderats och de vanligt förekommande problemen under drift har belysts. Forskningsprojektet Annex 52 Annex 52 Long-term performance measurement of GSHP systems serving commercial, institutional and multi-family building som är en del av IEA HPT TCP visar på behovet av att systematisk utvärdera bergvärmesystem. Detta examensarbete syftar till att utveckla och bidra till kunskap om hur bergvärmesystem kan utvärderas och att bidra med exempelstudier till Annex 52. Inom detta examensarbete har tre bergvärmesystem som betjänar flerbostadshus utvärderats och analyserats. Utvärderingen bestod av tre analyser. I den första analyserades driften av bergvärmesystemen och hur stabilt systemet har varit historiskt. Detta följdes av en detaljerad analys av olika nyckeltal för bergvärmesystemen. Årsverkningsgraden har beräknats för olika gränsdragningar vilka baseras på det tidigare arbetet utfört av SEPEMO. Inom detta examensarbete har även en metod tagits fram för att utvärdera verkningsgraderna för en värmepump baserat på de två temperaturnivåerna, köldbärarsidan och värmebärarsidan, som värmepumpen arbetar med under ett år. Till detta har en metod tagits fram om hur temperaturen kan normaliserats baserat på driften av värmepumparna för att kvantifiera en temperatur vardera för de två temperaturnivåerna. I den tredje utvärderingen jämfördes den beräknade medelfluidtemperaturen av köldbäraren i borrhålen med den uppmätta temperaturen. Till detta utfördes en känslighetsanalys av hur indata av dessa beräkningar påverkar resultaten.

La rhéologie à hauts taux de cisaillement pour deux polymères, le PEHD semi-cristallin et le PMMA amorphe a été étudiée. Des outils de rhéométrie classique, un rhéomètre plan-plan en mode dynamique, et un rhéomètre capillaire, ont été utilisés dans des conditions extrêmes (avec des filières pour la rhéométrie capillaire de diamètres allant jusqu'à 0,3 mm) mais les dépouillements de ces résultats ont été fait suivant les hypothèses conventionnelles en négligeant les instabilités et les phénomènes physiques qui interviennent lors de ces écoulements.Nous avons par la suite développé un modèle mathématique de l'écoulement dans un capillaire pour rendre compte de l'importance des différents phénomènes physiques qui peuvent avoir lieu dans des écoulements extrêmes, à savoir l'échauffement et la piezodépendance de la viscosité, la compressibilité et le glissement à la paroi. Les résultats du modèle développé ont été comparés avec les résultats expérimentaux.Nous avons aidé au développement d'une presse de microinjection originale et nous l'avons testée avec un moule de plaque instrumenté d'épaisseur allant jusqu'à 0,2 mm. Nous avons montré qu'il était possible de réaliser des pièces de qualité ce qui est avéré par des mesures de pression, vitesse et de température bien reproductibles. Nous avons exploité les données rhéologiques expérimentales dans la modélisation de la phase de remplissage avec le logiciel de calcul Rem3D. Des corrélations entre les mesures expérimentales et les calculs ont été réalisées en comparant l'évolution des pressions dans le système d'alimentation et dans l'empreinte. / Rheology at high shear rate for both polymers, semi-crystalline HDPE and amorphous PMMA was studied. Classical rheometry tools, plane-plane dynamic mode rheometer and capillary rheometer, were used in extreme conditions (with channels diameters for capillary rheometry up to 0.3 mm). However, analyses of these results were made following conventional assumptions neglecting instabilities and physical phenomena involved in these flows.We then developed a mathematical model of a capillary flow in to reflect the importance of different physical phenomena that can occur in extreme flows, namely heating, pressure dependency of viscosity, compressibility and the wall slip. The results of the developed model were compared with experimental results.We helped develop a press microinjection original and we tested it with instrumented plate mold with thickness up to 0.2 mm. We have shown that it is possible to make quality parts which are proven by well reproducible pressure, speed and temperature measurements. We used the experimental rheological data in filling phase modeling with the calculation software Rem3D. Correlations between experimental measurements and calculations were carried out by comparing the pressure in the filling system and the cavity.

Thermomechanical fatigue life prediction is important in the design of Ni-base superalloy components in gas turbine engines and requires a stress-strain analysis for accurate results. Crystal viscoplasticity models are an ideal tool for this stress-strain analysis of Ni-base superalloys as they can capture not only the anomalous yielding behavior, but also the non-Schmid effect, the strain rate dependence, and the temperature dependence of typically large grained directionally-solidified and single crystal alloys. However, the model is difficult to calibrate even for isothermal conditions because of the interdependencies between parameters meant to capture different but similar phenomena at different length scales, many tied to a particular slip system. The need for the capacity to predict the material response over a large temperature range, which is critical for the simulation of hot section gas turbine components, causes the determination of parameters to be even more difficult since some parameters are highly temperature dependent. Rapid parameter determination techniques are therefore needed for temperature-dependent parameterizations so that the effort needed to calibrate the model is reduced to a reasonable level. Specific parameter determination protocols are established for a crystal viscoplasticity model implemented in ABAQUS through a user material subroutine. Parameters are grouped to reduce interdependencies and a hierarchical path through the groups and the parameters within each group is established. This dual level hierarchy creates a logical path for parameter determination which further reduces the interdependencies between parameters, allowing for rapid parameter determination. Next, experiments and protocols are established to rapidly provide data for calibration of the temperature-dependencies of the viscoplasticity. The amount of data needed to calibrate the crystal viscoplasticity model over a wide temperature range is excessively large due to the number of parameters that it contains which causes the amount of time spent in the experimentation phase of parameter determination to be excessively large. To avoid this lengthy experimentation phase each experiment is designed to contain as much relevant data as possible. This is accomplished through the inclusion of multiple strain rates in each experiment with strain ranges sufficiently large to clearly capture the inelastic response. The experimental and parameter determination protocols were exercised by calibrating the model to the directionally-solidified Ni-bas superalloy DS-CM247LC. The resulting calibration describes the material's behavior in multiple loading orientations and over a wide temperature range of 20 °C to 1050 °C. Several parametric studies illustrate the utility of the calibrated model.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho apresenta uma estimativa a priori para o limite superior da distribuição de temperatura considerando um problema em regime permanente em um corpo com uma condutividade térmica dependente da temperatura. A discussão é realizada supondo que as condições de contorno são lineares (lei de Newton do resfriamento) e que a condutividade térmica é constante por partes (quando considerada como uma função da temperatura). Estas estimativas consistem em uma ferramenta poderosa que pode prescindir da necessidade de uma simulação numérica cara de um problema de transferência de calor não linear, sempre que for suficiente conhecer o valor mais alto de temperatura. Nestes casos, a metodologia proposta neste trabalho é mais eficaz do que as aproximações usuais que assumem tanto a condutividade térmica quanto as fontes de calor como constantes. / This article presents an a priori upper bound estimate for the steady-state temperature distribution in a body with a temperature-dependent thermal conductivity. The discussion is carried out assuming linear boundary conditions (Newton law of cooling) and a piecewise constant thermal conductivity (when regarded as a function of the temperature). These estimates consist of a powerful tool that may circumvent an expensive numerical simulation of a nonlinear heat transfer problem, whenever it suffices to know the highest temperature value. In these cases the methodology proposed in this work is more effective than the usual approximations that assume thermal conductivities and heat sources as constants.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho apresenta uma estimativa a priori para o limite superior da distribuição de temperatura considerando um problema em regime permanente em um corpo com uma condutividade térmica dependente da temperatura. A discussão é realizada supondo que as condições de contorno são lineares (lei de Newton do resfriamento) e que a condutividade térmica é constante por partes (quando considerada como uma função da temperatura). Estas estimativas consistem em uma ferramenta poderosa que pode prescindir da necessidade de uma simulação numérica cara de um problema de transferência de calor não linear, sempre que for suficiente conhecer o valor mais alto de temperatura. Nestes casos, a metodologia proposta neste trabalho é mais eficaz do que as aproximações usuais que assumem tanto a condutividade térmica quanto as fontes de calor como constantes. / This article presents an a priori upper bound estimate for the steady-state temperature distribution in a body with a temperature-dependent thermal conductivity. The discussion is carried out assuming linear boundary conditions (Newton law of cooling) and a piecewise constant thermal conductivity (when regarded as a function of the temperature). These estimates consist of a powerful tool that may circumvent an expensive numerical simulation of a nonlinear heat transfer problem, whenever it suffices to know the highest temperature value. In these cases the methodology proposed in this work is more effective than the usual approximations that assume thermal conductivities and heat sources as constants.

The electrical properties of ZnO and contacts to ZnO have been investigated using different techniques. Temperature dependent Hall (TDH) effect measurements have been used to characterize the as-received melt grown ZnO samples in the 20 – 330 K temperature range. The effect of argon annealing on hydrogen peroxide treated ZnO samples has been investigated in the 200 – 800oC temperature range by the TDH effect measurement technique. The experimental data has been analysed by fitting a theoretical model written in Matlab to the data. Donor concentrations and acceptor concentrations together with the associated energy levels have been extracted by fitting the models to the experimentally obtained carrier concentration data by assuming a multi-donor and single charged acceptor in solving the charge balance equation. TDH measurements have revealed the dominance of surface conduction in melt grown ZnO in the 20 – 40 K temperature range. Surface conduction effects have proved to increase with the increase in annealing temperature. Surface donor volume concentrations have been determined in the 200 – 800oC by use of theory developed by D. C. Look. Good rectifying Schottky contacts have been fabricated on ZnO after treating the samples with boiling hydrogen peroxide. Electrical properties of these Schottky contacts have been investigated using current-voltage (IV) and capacitance-voltage (CV) measurements in the 60 – 300 K temperature range. The Schottky contacts have revealed the dominance of predominantly thermionic emission at room temperature and the existence of other current transport mechanisms at temperatures below room temperature. Polarity effects on the Schottky contacts deposited on the O-polar and Zn-polar faces of ZnO have been demonstrated by the IV technique on the Pd and Au Schottky contacts at room temperature. Results obtained indicate a strong dependence of the Schottky contact quality on the polarity of the samples at room temperature. The quality of the Schottky contacts have also indicated their dependence on the type of metal used with the Pd producing contacts with the better quality as compared to the Au. Schottky barrier heights determined using temperature dependent IV measurements have been observed to increase with increasing temperature and this has been explained as an effect of barrier inhomogeneities, while the ones obtained from CV measurements have proved to follow the negative temperature coefficient of the II – VI semiconductor material, i.e. a decrease in barrier height with increasing temperature. However, the values have proved to be larger than the energy gap of ZnO, an effect that has been explained as caused by an inversion layer. Copyright / Dissertation (MSc)--University of Pretoria, 2010. / Physics / unrestricted

<p> Speleothems are calcium carbonate deposits, such as stalagmites, stalactites and flowstones, formed in a cave environment by loss of carbon dioxide from saturated groundwaters. Variations in the 18o/16o ratio of calcite are related to changes in depositional temperature provided that the speleothem formed in isotopic equilibrium with its seepage water (conditions characterised by slow coloss and no evaporation of seepage water). Variations in 18o/16o of the seepage water will also be reproduced in the calcite but allowance for this effect can be made if 18o/16o ratio of the source (ocean water) can be estimated (from deep sea sediment cores) and if the influence of temperature on 18o/16o ratio of precipitation at the site can be determined. Because cave temperatures closely approximate mean annual surface temperature, the axial 18o/16o record of a speleothem is therefore an indication of paleoclimate and of temperature change over the period of its growth. </p> <p> The frequency distribution of age measurements for several speleothems from an area may also be used as a paleoclimatic indicator because cold or glacial conditions above the cave will inhibit speleothem growth by freezing water at the surface and removing vegetation and soil cover, the main source of CO2 for the limestone dissolution-reprecipitation process. </p> <p> Pure, non-porous calcite speleothems from several limestone regions have been dated in this study by the 230Th/234U method, and in cases of uranium-rich speleothems, by the 231Pa/230Th method also. For ten such cases, examined, good agreement of ages determined by both dating methods was found. </p> <p> Relatively few deposits however, have shown deposition under isotopic equilibriwn conditions, due probably to the well-ventilated nature of the caves studied. </p> <p> The age distribution for speleothem from Cascade Cave on Vancouver Island, B.C., indicates growth during the mid-Wisconsin interstadial dated as 65 -30,000 yrs. B.P. Stable isotope profiles for two speleothems which grew over this period both show values of 18o/16o ratios of calcite which are significantly lower than calcite growing in the cave today. This is the first clearly-defined record of such an occurence (in previous work, 18o/16o of fossil speleothem was generally greater than modern). Using estimates of the change in 18o/16o of ocean water from a Pacific deep sea core, and the value determined by Dansgaard (1964) for the temperature dependence of 18o/16o of precipitation for oceanic sites, a realistic paleotemperature record is derived. The results indicate that temperatures at the Cascade Cave site were about 4.0°C , 64,000 yrs. ago· and gradually declined to 0°c by 35,000 yrs. ago. These data are consistent with the findings of Canadian workers from 14c and palynological studies of fossil organic matter in the area, and do not support the proposal by some American workers of a major glaciation occurring between 35 - 40,000 yrs. B.P. </p> <p> The age distribution for 140 analyses of 82 speleothems collected from caves in north-west England show abundant deposition during the periods 130 -90,000 yrs. B.P. and 13,000 yrs. B.P. to present, with limited growth over the periods > 350 -170,000 yrs. B.P. and 70 -35,000 yrs. B.P. No ages were found to lie within the periods 170 -140,000 yrs. B.P. and 35-15,000 yrs. B.P. These intervals are correlated to the Wolstonian and Devensian glaciations respectively. </p> <p> Only four speleothems were found to have grown in isotopic equilibrium with their seepage waters, and one of these showed periods of non-equilibrium deposition. In contrast to the Vancouver Island results, 18o/16o all ratios were found to be greater than or equal to modern, indicating that the apparent oceanic location of this site is not expressed in the on the value for temperature dependence of 18o/16o precipitation. </p> <p> An oxygen isotope profile for a flowstone dated between 126,000 and 109, 000 yrs. B.P. shows 18o/16o ratios commencing at values slightly lower than for modern calcite and shifting to still lower values at about 112, 000 yrs. B.P. This shift may indicate a cooling event perhaps carrelative with the isotope stage 5e-5d transition seen in the deep sea core record. A profile for a flowstone over the period 290 -190,000 yrs. B.P. shows excellent correlation to interglacial stages 9e and 7c seen in the deep sea core record, and a pronounced growth hiatus dated at about 250 210,000 yrs. B.P. correlates with glacial stage 8. These are the first speleothem results to show a climatic record beyond 200,000 yrs. B.P. </p> <p> The differences in 18o/16o behaviour for speleothems from the two locations (N .E. Pacific and ..E. Atlantic) are interpreted in terms of their relative proximity to the ocean, potential for exchange of water vapour and 'rainout' by airmasses moving towards the cave sites, and possibility of change in meteorological conditions (principally storm track) over the periods studied. </p> <p> In a subsidiary study, evidence for major sea level lowering during the Illinoian glaciation is recognised by age determinations on the calcite core of speleothems collected at 45m below present sea level from a 'blue hole' near Andros Island in the Bahamas. </p> <p> The possibility of applying the 234U/238U dating method to speleothem is also investigated in this work, by the analysis of modern calci tes and their seepage waters, using a new method for uranium extraction from groundwater. However the variations in 234U/238U ratios observed over short distances in the same cave demonstrate that estimation of initial fossil 234U/238U in the speleothem cannot simply be made by averaging modern ratios for the cave. </p> <p> Consideration is also given to the temperature dependent distribution of trace elements in calcite, particularly magnesium and strontium. Analyses of modern calcites and waters show that Mg incorporation is strongly temperature dependent whereas Sr is not. The possibility of using Mg variations in fossil speleothem as indication of temperature change is briefly examined but the results for one sample are found to be inconclusive. </p> / Thesis / Doctor of Philosophy (PhD)

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