A radiação térmica é frequentemente considerada um mecanismo de transferência de calor muito importante em processos de combustão em alta pressão, devido à presença de meios participantes e às altas temperaturas envolvidas. Resolver a radiação térmica em meios participantes é um problema complexo devido à natureza integro-diferencial da equação governante e à dependência espectral altamente irregular das propriedades de radiação. Atualmente, o método mais preciso para resolver a integração espectral é o método linha-porlinha (LBL), que possui um custo computacional muito elevado. Para contornar essa dificuldade, o problema espectral é geralmente resolvido usando modelos espectrais e, consequentemente, a equação da transferência radiativa (RTE) é simplificada. Um destes modelos é o da soma-ponderada-de-gases-cinza (WSGG), que substitui o comportamento espectral altamente irregular do coeficiente de absorção, por bandas de coeficientes de absorção uniforme e tem mostrado um bom desempenho em diversas aplicações, mesmo sendo um modelo bastante simplificado. Entretanto, recentemente alguns autores não obtiveram bons resultados ao tentar aplicar o WSGG a problemas de combustão em alta pressão. Este artigo desenvolve um modelo WSGG para CO2 e H2O em condições de alta pressão. Para validar o modelo, a emitância total é calculada usando os coeficientes WSGG e comparada à solução do LBL obtida usando o banco de dados espectrais HITEMP 2010. Os resultados mostraram grande convergência entre os valores de emitância de ambos os métodos, mesmo para valores de alta pressão, tanto para o CO2 quanto para H2O, provando que o método WSGG é aplicável a condições de alta pressão. O modelo também foi validado pelo cálculo do fluxo de calor e termo fonte radiativo, e comparando-os com os obtidos através do método LBL. O H2O teve melhores resultados para baixas pressões, enquanto o CO2 apresentou melhores resultados para pressões mais altas. O efeito da pressão total sobre a solução de LBL foi maior para o H2O, o que pode ser um dos motivos pelo qual os desvios foram maiores para os casos de alta pressão. / Thermal radiation is often a very important heat transfer mechanism in high pressure combustion processes due to the presence of participating media and the high temperatures involved. Solving thermal radiation in participating media is a tough problem due to the integro-differential governing equation and the complex spectral dependence of radiation properties. Currently, the most accurate method to solve the spectral integration is the line-byline (LBL) method, which has a very high computational cost. In order to avoid this drawback the spectral problem is usually solved using spectral models, and as a consequence the radiative transfer equation (RTE) is simplified. One of the models is the weighted-sum-ofgray- gases (WSGG) which replaces the highly irregular spectral behavior of the absorption coefficient by bands of uniform absorption coefficients, and has shown great performance a lot of applications even though it is a very simple model. However, recently some authors didn’t have good results when trying to apply the WSGG to high pressure combustion problems. This thesis develops a WSGG model for both CO2 and H2O on high pressure conditions. In order to validate the model the total emittance is calculated using the WSGG coefficients and compared to the LBL solution which was obtained using the HITEMP 2010 spectral emissivity database. The results showed that the emittance values from both methods were very close even for high pressure values for both CO2 and H2O proving that the WSGG method is applicable to high pressure conditions. The model was also validated by calculating the radiative heat flux and source, and comparing them with the LBL method. H2O had better results for low pressures while CO2 had better results for higher pressures. The effect of total pressure on the LBL solution was higher for H2O, which might be the reason why deviations were higher at high pressure values.

The presented thesis focuses on study of transport and thermoelastic properties of materials under conditions of planetary interiors by means of high-pressure experimental tools and finite element modeling, and their role in the dynamics and states of cores of terrestrial planets. Experiments in laser-heated diamond anvil cell (LHDAC) in combination with numerical simulations of heat transfer in DAC are shown to yield information on thermal conductivity of a pressurized sample. The novel technique consists of one-sided laser heating and double-sided temperature measurements and utilizes a precise determination of several parameters in course of the experiment, including the sample geometry, laser beam power distribution, and optical properties of employed materials. The pressure-temperature conditions at the probed portion of the sample are, however, not uniform. To address this problem, thermal pressure in the laser-heated diamond anvil cell and anisotropic thermal conductivity originating from the texture development upon uniaxial compression have been studied by means of numerical simulations. The method for determination of thermal conductivity is applied to iron at pressures up to 70 GPa and temperatures of 2000 K, meeting the Earth’s lower mantle conditions and covering Mercury’s entire core. The obtained results are extrapolated to the conditions of the Earth’s core-mantle boundary using a theoretical model of the density dependence of thermal conductivity of metals and published values on Grüneisen parameter and bulk modulus. After considering the effect of minor core elements, the obtained value at these conditions supports case for the downward revision of the thermal conductivity in the core. From the point of view of core dynamics and energy budget, the lower thermal conductivity implies more favorable conditions to drive the dynamo. Similar scenario applies for Mercury where, for high values of thermal conductivity, heat flux conducted along the iron-core adiabat exceeds the actual heat flux through the core-mantle boundary. This leads to a negative rate of entropy production in the core that makes it impossible to sustain the dynamo process presumably responsible for the observed magnetic field of Mercury.

A radiação térmica é frequentemente considerada um mecanismo de transferência de calor muito importante em processos de combustão em alta pressão, devido à presença de meios participantes e às altas temperaturas envolvidas. Resolver a radiação térmica em meios participantes é um problema complexo devido à natureza integro-diferencial da equação governante e à dependência espectral altamente irregular das propriedades de radiação. Atualmente, o método mais preciso para resolver a integração espectral é o método linha-porlinha (LBL), que possui um custo computacional muito elevado. Para contornar essa dificuldade, o problema espectral é geralmente resolvido usando modelos espectrais e, consequentemente, a equação da transferência radiativa (RTE) é simplificada. Um destes modelos é o da soma-ponderada-de-gases-cinza (WSGG), que substitui o comportamento espectral altamente irregular do coeficiente de absorção, por bandas de coeficientes de absorção uniforme e tem mostrado um bom desempenho em diversas aplicações, mesmo sendo um modelo bastante simplificado. Entretanto, recentemente alguns autores não obtiveram bons resultados ao tentar aplicar o WSGG a problemas de combustão em alta pressão. Este artigo desenvolve um modelo WSGG para CO2 e H2O em condições de alta pressão. Para validar o modelo, a emitância total é calculada usando os coeficientes WSGG e comparada à solução do LBL obtida usando o banco de dados espectrais HITEMP 2010. Os resultados mostraram grande convergência entre os valores de emitância de ambos os métodos, mesmo para valores de alta pressão, tanto para o CO2 quanto para H2O, provando que o método WSGG é aplicável a condições de alta pressão. O modelo também foi validado pelo cálculo do fluxo de calor e termo fonte radiativo, e comparando-os com os obtidos através do método LBL. O H2O teve melhores resultados para baixas pressões, enquanto o CO2 apresentou melhores resultados para pressões mais altas. O efeito da pressão total sobre a solução de LBL foi maior para o H2O, o que pode ser um dos motivos pelo qual os desvios foram maiores para os casos de alta pressão. / Thermal radiation is often a very important heat transfer mechanism in high pressure combustion processes due to the presence of participating media and the high temperatures involved. Solving thermal radiation in participating media is a tough problem due to the integro-differential governing equation and the complex spectral dependence of radiation properties. Currently, the most accurate method to solve the spectral integration is the line-byline (LBL) method, which has a very high computational cost. In order to avoid this drawback the spectral problem is usually solved using spectral models, and as a consequence the radiative transfer equation (RTE) is simplified. One of the models is the weighted-sum-ofgray- gases (WSGG) which replaces the highly irregular spectral behavior of the absorption coefficient by bands of uniform absorption coefficients, and has shown great performance a lot of applications even though it is a very simple model. However, recently some authors didn’t have good results when trying to apply the WSGG to high pressure combustion problems. This thesis develops a WSGG model for both CO2 and H2O on high pressure conditions. In order to validate the model the total emittance is calculated using the WSGG coefficients and compared to the LBL solution which was obtained using the HITEMP 2010 spectral emissivity database. The results showed that the emittance values from both methods were very close even for high pressure values for both CO2 and H2O proving that the WSGG method is applicable to high pressure conditions. The model was also validated by calculating the radiative heat flux and source, and comparing them with the LBL method. H2O had better results for low pressures while CO2 had better results for higher pressures. The effect of total pressure on the LBL solution was higher for H2O, which might be the reason why deviations were higher at high pressure values.

Made available in DSpace on 2016-06-02T19:56:57Z (GMT). No. of bitstreams: 1 6640.pdf: 3550944 bytes, checksum: d30528732e74d92750389a70e54b8387 (MD5) Previous issue date: 2015-01-23 / Universidade Federal de Sao Carlos / The gas filtration process has several advantages, such as to prevent damage to the environment and health of living beings and to avoid damage in the equipment used in various industrial processes. The filter media applied in these processes can be made of various materials, including metal, fiberglass, polypropylene, polyester and cellulose, with the latter being highlighted by its low cost. The objective of this study is to evaluate the performance of the cellulose filters RAD + and RAD Plus, through permeability, filtration and porosity of the filter cake tests, when subjected to high pressures using the experimental apparatus located in the Environmental Control Laboratory in the Chemical Engineering Department at UFSCar and talc as particulate matter. The working conditions used in the experiments were pressures of 93, 193, 293, 393 and 493kPa, for the permeability tests, and 93, 293 and 493kPa, for the filtration tests. In the permeability tests, the superficial velocity of the gas was varied from 0 to 0.25m/s, while in the filtration tests, the velocities of filtration were 0.05 and 0.06 m/s. The porosity of the cake filtration was determined by mathematics correlations. The permeability constants calculated for both filter media could be considered constant with pressure. For filtration assays, it could be observed that increasing the pressure of the system was the mass withheld by filter media increased for the same pressure drop, without any significant variation with the filtration velocities studied. It was also observed an increase in porosity and a decrease in the resistance of cake filtration when the system pressure was raised. / O processo de filtração de gases possui diversas vantagens, tanto para prevenção de danos ao meio ambiente e saúde dos seres vivos quanto para prevenção de danos a equipamentos em diversos processos industriais. Os meios filtrantes usados nesses processos podem ser de vários materiais, entre eles os metálicos, de fibra de vidro, de polipropileno, de poliéster e de celulose, com este último sendo destacado pelo seu baixo custo. O objetivo deste trabalho é avaliar o desempenho dos filtros de celulose RAD + e RAD Plus, através de ensaios de permeabilidade, filtração e porosidade da torta de filtração, quando submetidos a altas pressões usando o aparato experimental localizado no Laboratório de Controle Ambiental no Departamento de Engenharia Química da UFSCar e talco como material particulado. As condições de trabalho para realização dos experimentos foram as pressões de 93, 193, 293, 393 e 493kPa, para os ensaios de permeabilidade, e 93, 293 e 493kPa, para os ensaios de filtração. Nos ensaios de permeabilidade, variou-se a velocidade superficial do gás de 0 a 0,25m/s, enquanto que nos ensaios de filtração as velocidades superficiais de filtração foram de 5 e 6 cm/s. A determinação da porosidade da torta foi realizada através de correlações matemáticas. Observou-se a partir dos resultados obtidos, que as constantes de permeabilidade calculadas para ambos os meios filtrantes puderam ser consideradas constantes com a pressão. Para os ensaios de filtração pôdese observar que com o aumento da pressão do sistema houve um aumento da massa retida pelos meios filtrantes para uma mesma queda de pressão, não havendo variação significativa com as velocidades de filtração estudadas. Também foi observado um aumento da porosidade e uma diminuição da resistência da torta de filtração a medida que a pressão do sistema foi aumentada.

A radiação térmica é frequentemente considerada um mecanismo de transferência de calor muito importante em processos de combustão em alta pressão, devido à presença de meios participantes e às altas temperaturas envolvidas. Resolver a radiação térmica em meios participantes é um problema complexo devido à natureza integro-diferencial da equação governante e à dependência espectral altamente irregular das propriedades de radiação. Atualmente, o método mais preciso para resolver a integração espectral é o método linha-porlinha (LBL), que possui um custo computacional muito elevado. Para contornar essa dificuldade, o problema espectral é geralmente resolvido usando modelos espectrais e, consequentemente, a equação da transferência radiativa (RTE) é simplificada. Um destes modelos é o da soma-ponderada-de-gases-cinza (WSGG), que substitui o comportamento espectral altamente irregular do coeficiente de absorção, por bandas de coeficientes de absorção uniforme e tem mostrado um bom desempenho em diversas aplicações, mesmo sendo um modelo bastante simplificado. Entretanto, recentemente alguns autores não obtiveram bons resultados ao tentar aplicar o WSGG a problemas de combustão em alta pressão. Este artigo desenvolve um modelo WSGG para CO2 e H2O em condições de alta pressão. Para validar o modelo, a emitância total é calculada usando os coeficientes WSGG e comparada à solução do LBL obtida usando o banco de dados espectrais HITEMP 2010. Os resultados mostraram grande convergência entre os valores de emitância de ambos os métodos, mesmo para valores de alta pressão, tanto para o CO2 quanto para H2O, provando que o método WSGG é aplicável a condições de alta pressão. O modelo também foi validado pelo cálculo do fluxo de calor e termo fonte radiativo, e comparando-os com os obtidos através do método LBL. O H2O teve melhores resultados para baixas pressões, enquanto o CO2 apresentou melhores resultados para pressões mais altas. O efeito da pressão total sobre a solução de LBL foi maior para o H2O, o que pode ser um dos motivos pelo qual os desvios foram maiores para os casos de alta pressão. / Thermal radiation is often a very important heat transfer mechanism in high pressure combustion processes due to the presence of participating media and the high temperatures involved. Solving thermal radiation in participating media is a tough problem due to the integro-differential governing equation and the complex spectral dependence of radiation properties. Currently, the most accurate method to solve the spectral integration is the line-byline (LBL) method, which has a very high computational cost. In order to avoid this drawback the spectral problem is usually solved using spectral models, and as a consequence the radiative transfer equation (RTE) is simplified. One of the models is the weighted-sum-ofgray- gases (WSGG) which replaces the highly irregular spectral behavior of the absorption coefficient by bands of uniform absorption coefficients, and has shown great performance a lot of applications even though it is a very simple model. However, recently some authors didn’t have good results when trying to apply the WSGG to high pressure combustion problems. This thesis develops a WSGG model for both CO2 and H2O on high pressure conditions. In order to validate the model the total emittance is calculated using the WSGG coefficients and compared to the LBL solution which was obtained using the HITEMP 2010 spectral emissivity database. The results showed that the emittance values from both methods were very close even for high pressure values for both CO2 and H2O proving that the WSGG method is applicable to high pressure conditions. The model was also validated by calculating the radiative heat flux and source, and comparing them with the LBL method. H2O had better results for low pressures while CO2 had better results for higher pressures. The effect of total pressure on the LBL solution was higher for H2O, which might be the reason why deviations were higher at high pressure values.

En 1980, une excitation électronique inédite des électrons supraconducteurs a été mise en évidence par spectroscopie Raman dans le composé 2H-NbSe2. Cette excitation semble pouvoir être associée à un mode collectif d’amplitude du paramètre d’ordre supraconducteur.Ce mode, analogue au boson de Higgs dans le modèle standard, est normalement non couplé à la lumière mais serait observable dans le cas de 2H-NbSe2 via un couplage de la supraconductivité avec une autre phase exotique appelée onde de densité de charge.Cette thèse a consisté à utiliser la spectroscopie Raman sous haute pression pour mettre cette théorie à l’épreuve de deux façons. D’une part, en détruisant l’onde de densité de charge dans 2H-NbSe2 sous haute pression et voir si celle-ci est réellement nécessaire à l’observation du mode Higgs. D’autre part, en cherchant de nouveaux exemples d’observation du mode de Higgs dans d’autres composés (2H-TaS2, 2H-TaSe2,...) où la supraconductivité coexiste avec une onde de densité de charge / In 1980, a unique electronic excitation of the superconducting electrons was observed in 2H-NbSe2 by Raman spectroscopy. This excitation can be associated to a collective mode of the amplitude of the superconducting order parameter. This mode, analogous to the Higgs boson in the standard model, is not coupled to light but would be visible in 2H-NbSe2through a coupling to another exotic phase called charge density wave.This thesis consisted in using Raman spectroscopy under high pressures to tackle thistheory in two different ways. Firstly, by inducing a collapse of the charge density wave athigh pressure and see if the coupling to this phase really is a requisite to the visibility of the Higgs mode. Secondly, by searching for new exemples of Higgs modes in other compounds (2H-TaS2, 2H-TaSe2,...) where superconductivity coexists with a charge density wave

Thesis (M. Tech. (Engineering: Mechanical)) -- Central University of Technology, Free State, 2013 / This research examines the suitability of Additive Manufacturing (AM) for manufacturing dies used in aluminium high pressure die casting. The study was guided by the following objectives: • The reviews of applicable literature sources that outline technical and application aspects of AM in plastic injection moulds and the possibilities of applying it to high pressure casting die. • To introduce AM grown die components in die manufacture. Further, to develop a methodology that will allow industry to apply AM technology to die manufacture. • Revolutionise the way die manufacture is done. The potential for AM technologies is to deliver faster die manufacture turnaround time by requiring a drastically reduced amount of high level machining accuracy. It also reduces the number of complex mechanical material removal operations. Fewer critical steps required by suitable AM technology platforms able to grow fully dense metal components on die casting tools able to produce production runs. • Furthermore, promising competitive advantages are anticipated on savings to be attained on the casting processing side. AM technology allows incorporation of features in a die cavity not possible to machine with current machining approaches and technology. One such example is conformal cooling or heating of die cavities. This approach was successfully used in plastic injection mould cavities resulting in savings on both the part quality as well as the reduction on cycle time required to produce it (LaserCUSING®, 2007). AM technology has evolved to a point where as a medium for fast creation of an object, it has surpassed traditional manufacturing processes allowing for rapidly bridging the gap between ideas to part in hand. The suitability of the AM approach in accelerating the die manufacturing process sometime in the near future cannot be dismissed or ignored. The research showed that there is promise for application of the technology in the not too distant future. In the South African context, the current number and affordability of suitable AM platforms is one of the main stumbling blocks in effecting more widespread applied research aimed at introduction of the technology to die manufacture.

This investigation address the effect that pressure, p, and temperature, T, have on 4f-states of the rare-earth elements in the isostructural YbRh2Si2, EuCo2Ge2, and EuCu2Ge2 compounds. Upon applying pressure, the volume of the unit cell reduces, enforcing either the enhancement of the hybridization of the 4f-localized electrons with the ligand or a change in the valence state of the rare-earth ions. Here, we probe the effect of a pressure-induced lattice contraction on these system by means of electrical resistivity, from room temperature down to 100 mK. At ambient pressure, the electrical resistivity of YbRh2Si2 shows a broad peak at 130 K related to the incoherent scattering on the ground state and the excited crystalline electrical field (CEF) levels. At T_N = 70 mK, YbRh2Si2 undergoes a magnetic phase transition. Upon applying pressure up to p_1 = 4 GPa , T_N increases monotonously while the peak in the electrical resistivity is shifted to lower temperatures. For p < p_1 a different behavior is observed; namely, T_N depends weakly on the applied pressure and a decomposition of the single peak in the electrical resistivity into several shoulders and peaks occurs. Above p_2 = 9 GPa, the electrical resistivity is significantly reduced for T < 50 K and this process is accompanied by a sudden enhancement of T_N. Thus, our results confirm the unexpected behavior of the magnetization as function of pressure reported by Plessel et al. The small value of the magnetic ordering temperature for p < p_2 and the strength of the mechanism that leads to the peaks and shoulders in the electrical resistivity suggest that the f-electrons are still screened by the conduction electrons. Therefore, the observed behavior for pressures lower than p_2 might be a consequence of the competition of two different types of magnetic fluctuations (seemingly AFM and FM). Furthermore, the results suggest that a sudden change of the CEF scheme occurs at pressures higher than p_1, which would have an influence on the ground state. Additionally, a comparison of the pressure dependent features in the electrical resistivity of YbRh2Si2 with similar maxima in other isostructural YbT2X2 (T = transition metal; X = Si or Ge) compounds was performed. For the comparison, a simple relation that considers the Coqblin-Schrieffer model and the hypothesis of Lavagna et al. is proposed. A systematic behavior is observed depending on the transition metal; namely, it seems that the higher the atomic radii of the T-atom the smallest the pressure dependence of the maximum in the electrical resistivity, suggesting a weaker coupling of localized- and conduction-electrons. It is also observed that an increase in the density of conduction electrons reduces the pressure dependence of the characteristic Kondo temperature. The mechanism responsible for the sudden enhancement of T_N in YbRh2Si2 at about p_2 is still unknown. However two plausible scenarios are discussed. The Eu-ions in EuCo2Ge2 and EuCu2Ge2 have a divalent character in the range 100 mK < T < 300 K. Therefore, these systems order magnetically at T_N = 23 K and T_N = 12 K, respectively. The studies performed on EuCo2Ge2 and EuCu2Ge2 as a function of pressure suggest that a change to a non-magnetic trivalent state of the Eu-ions might occur at zero temperature for pressures higher than 3 GPa and 7 GPa, respectively. A common and characteristic feature on EuCo2Ge2 and EuCu2Ge2 is the absence of a clear first order transition from the divalent to the trivalent state of the Eu-ions at finite temperature for p > 3 GPa and for p > 7 GPa, respectively. In other isostructural Eu-based compounds, a discontinuous and abrupt change in the thermodynamic and transport properties associated to the valence transition of the Eu-ions is typically observed at finite temperatures. In contrast, the electrical resistivity of EuCo2Ge2 and EuCu2Ge2 changes smoothly as a function of pressure and temperature. The analysis of the the electrical resistivity of EuCo2Ge2 suggest that a classical critical point might be close to the AFM-ordered phase, being a hallmark of this compound. The overall temperature dependence of the the electrical resistivity of EuCo2Ge2 changes significantly at 3 GPa; therefore, it seems that the system suddenly enters to a T-dependent valence-fluctuating regime. Additionally, the pressure-dependent electrical-resistivity isotherms show a step-like behavior. Thus, it is concluded that discontinuous change of the ground state might occur at 3 GPa. The electrical resistivity of EuCu2Ge2 at high pressure is characterized by a negative logarithmic T-dependence in the pressure range 5 GPa < p < 7 GPa for T > T_N and by a broad peak in the pressure dependent residual resistivity, whose maximum is located at 7.3 GPa. The first behavior resembles the incoherent scattering process typical for an exchange coupling mechanism between the localized electrons and the ligand. This and the peak effect in the local 4f susceptibility observed in NMR measurements are consistent with such a coupling mechanism. Thus, it would be for the first time that a dense Eu-based compound like EuCu2Ge2 show such a behavior. Combining the results of the experiment performed at high pressures on EuCu2Ge2 with the studies performed in the EuCu2(Ge1-xSix)2 series, a crossover from an antiferromagnetically ordered state into a Fermi-liquid state for pressures higher than 7.3 GPa may be inferred from the analysis. Therefore, it may be possible that the sudden depopulation of 4f-level occur mediated by quantum fluctuation of the charge due to a strong Coulomb repulsion between the localized-electrons and the ligand. This phenomenon would explain the broad peak in the residual resistivity. To our knowledge, this would be the first Eu-based compound, isostructural to ThCr2Si2, that show such a transition as function of pressure at very low temperatures.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 160-167). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 160-167). Also available on the Internet.