Dissertations / Theses on the topic 'Thermal propertie'

Orientador: Flavia Maria Netto
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos
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Resumo: Em algumas aplicações em alimentos, a indução da geleificação a temperaturas altas pode ser indesejável. Alguns produtos de soja quando submetidos ao tratamento térmico, mesmo que moderado, desenvolvem sabores e aromas não desejáveis, limitando sua aplicação. A produção de géis a frio envolve essencialmente duas etapas: a formação de uma dispersão estável de agregados de proteína obtida após o aquecimento da solução protéica e a indução da geleificação por redução do pH ou adição de sal. Ao contrário da geleificação induzida pelo calor, no processo de geleificação a frio a etapa de ativação da proteína, a desnaturação térmica, não ocorre simultaneamente às etapas de agregação e geleificação, permitindo determinar as propriedades dos agregados após o aquecimento e as propriedades finais do gel. Embora géis termicamente formados de proteínas de soja tenham sido extensivamente estudados, pouco se conhece sobre a capacidade das proteínas de soja de formarem gel a frio. O presente estudo investigou o efeito do tratamento térmico na fase de produção do isolado protéico de soja (IPS) e o efeito da adição de CaCl2 na formação a frio de estrutura tipo gel de IPS. IPS foi obtido a partir de farinha desengordurada de soja comercial, e, após a etapa de neutralização, tratado a 60 ou 80oC por 15 ou 30 min., variando-se a concentração protéica (3 e 5%), para obtenção de isolados com agregados de diferentes propriedades físico-químicas. Géis foram obtidos a frio a partir de dispersões com 12 e 14% de proteína (p/p), com e sem a adição de CaCl2 (5 e 15 mM). A desnaturação protéica e agregação foram avaliadas por análises de calorimetria diferencial de varredura (CDV), turbidez, solubilidade em água, sulfidrila livre, hidrofobicidade superficial e cromatografia líquida de alta eficiência de exclusão molecular. Os resultados indicaram desnaturação parcial, maior grau de agregação e aumento da massa molar dos agregados com o incremento da concentração da proteína no tratamento prévio dos IPSs. Os isolados não tratado termicamente e o tratado a 60ºC não formaram gel em nenhuma das condições experimentais utilizadas, enquanto para os IPSs tratados a 80ºC, os valores de G¿, G¿¿ e tan d foram característicos de um sólido viscoelástico, sugerindo a formação de uma matriz tridimensional estável, independente da adição de CaCl2. Os géis protéicos de soja induzidos a frio sem a presença de sal foram mais translúcidos, de estrutura menos porosa e maior capacidade de retenção de água (91,9 ¿ 82,5%) do que os obtidos com 15 mM de CaCl2. Os géis formados pela adição de 5 e 15 mM de CaCl2 foram mais opacos e consistentes do que os géis sem adição de sal. Porém, os géis formados pela adição de 15 mM CaCl2 foram mais esbranquiçados, indicando a formação de grandes agregados e com menor capacidade de retenção de água (51,2 ¿ 76,1%). Os resultados mostraram que os géis formados a frio dos IPSs tratados termicamente apresentaram características macroscópicas diferentes, atribuídas ao tipo de agregado formado na etapa de aquecimento e à quantidade de CaCl2 adicionada posteriormente. Por sua vez, o tipo de agregado formado na etapa de aquecimento teve influência principalmente da concentração de proteína e da temperatura de aquecimento. A adição de CaCl2 não foi determinante para a formação do gel, mas teve um importante papel em sua estruturação. Concluiu-se que a manipulação das condições térmicas pode conduzir à formação de agregados e géis de proteínas de soja com propriedades físico-químicas desejáveis
Abstract: The induction of gelation by high temperatures can be undesirable in some food applications. When submitted to the thermal treatment, that even moderate, some products of soy may develop not desirable flavors and aromas, limiting its application. The preparation of protein gels using cold-gelation consists of two steps: a stable dispersion of protein aggregation is obtained after heating of a solution of native proteins and gelation induced by lowering the pH or by adding salt. In contrast with the heatinduced gelation, the stage of activation of the protein in the cold-gelation process is previous to the stages of aggregation and gelation, what it allows to determine the properties of aggregates after heating and thereby control final gels properties. Although heat-induced gelation of soy protein has been extensively studied, little is known about the capacity of soy protein to form cold-set gel. The present study has investigated the effects that heat-treatment during soy protein isolates preparations (SPI) in the cold-set gelation by the addition of CaCl2. SPI was obtained from soy defatted flour and heated at 60 or 80°C after the neutralization step, followed of freeze-dried. Protein concentrations of 3 and 5% and heating times of 15 and 30 min were used in order to obtain aggregates with different physical properties. Cold-set gels were obtained from 12 and 14 % (w/w) of protein dispersions, with or without CaCl2 addition (5 and 15 mM). Denaturation followed by aggregation was verified by differential scanning calorimetry (DSC), turbidity, water solubility, free sulfhydryl groups (SH), superficial hydrophobicity and size exclusion-high performance liquid chromatography (SE-HPLC). The results indicated higher aggregation degree and increased molar mass of aggregates when the protein concentration was enhanced to 5% in the pre-heating of the SPIs. The isolates without heat-treatment and the isolates heated at 60°C did not form gels in any of the experimental conditions utilized, while for the IPSs heated at 80ºC, the values of G¿, G¿¿ and tan d were characteristic of a viscous-elastic solid, suggesting the formation of a stable three-dimensional matrix, independent of CaCl2 addition. The cold-induced soy protein gels without the presence of salt were more translucent and with lower porous structure and higher water retention capacity (91.9 - 82.5%), than those obtained with 15 mM of CaCl2. The gels obtained by 5 and 15 mM of CaCl2 addition were opaque and more consistent that gels without the presence of salt. However, gels obtained by 15 mM of CaCl2 were whitened, indicating the formation of large aggregates with lower water retention capacity (51.2 - 76.1%). The results showed that the cold-set gels formed from heat treated SPIs exhibited different macroscopic characteristics, attributable to the type of aggregate formed in the heating step and to the quantity of posterior addition of CaCl2. At the same time, the type of aggregate formed in the heating step was mainly influenced by protein concentration and denaturation degree. The CaCl2 addition was not determining for gel formation but has an important role on his structure. It was concluded that manipulation of thermal conditions can lead to aggregates and soy protein isolate cold-set gels formation with desirable physicalchemical properties
Doutorado
Nutrição Experimental e Aplicada à Tecnologia de Alimentos
Doutor em Alimentos e Nutrição

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.

La technologie de pulvérisation magnétron par impulsions de haute puissance (HiPIMS) a été développée et est considérée comme une méthode efficace pour la préparation des films. La technologie HiPIMS permet une bien plus grande flexibilité pour ajuster la structure et les performances du film, conduisant à des films avec des propriétés uniques qui sont souvent irréalisables dans les autres approches PVD. Cependant, le mécanisme sous-jacent du plasma pour soutenir la croissance du film impliqué est actuellement flou. De plus, la technologie HiPIMS est limitée au laboratoire, de nombreux films aux propriétés souhaitables n'ont pas été explorés dans le cadre de la pulvérisation HiPIMS. Dans ce travail, (i) le l’origine de la structure cohérente du plasma haute densité (les « spokes ») dans la décharge HiPIMS et (ii) comment la structure et les propriétés des films de TaC/a-C:H et HfC/a-C:H sont gérées par HiPIMS ont été étudiés. Dans l'étude du mécanisme de formation des « spokes », basée sur la relation de dispersion du plasma HiPIMS et l'évolution du couplage entre deux ondes azimutales, un modèle d'onde induit par couplage a été proposé. Dans l'étude des films TaC/a-C:H et HfC/a-C:H, les états des liaisons chimiques, la structure, la morphologie, les propriétés mécaniques et tribologiques, la stabilité thermique ainsi que la résistance à l'oxydation des films ont été étudiés. En comparaison avec ces films déposés par pulvérisation magnétron DC, il est démontré que la technologie HiPIMS permet une stratégie potentielle pour préparer des films TaC/a-C:H et HfC/a-C:H plus performants en termes de dureté, de coefficient de frottement et de résistance à l'usure, de résistance à l'oxydation et de stabilité thermique en modulant l'état de liaison chimique et la structure nanocomposite des films à travers un plasma réactif
High Power Impulse Magnetron Sputtering technology (HiPIMS) has been developed and considered as an effective method for film preparation. HiPIMS technology allows for much greater flexibility for manipulating film structure and performance, leading to films with unique properties that are often unachievable in the other PVD approaches. However, the underlying plasma mechanism for supporting film growth is currently blurred. Moreover, HiPIMS technology is still stationed in the laboratory, many films with desirable properties have not been explored under HiPIMS framework. In this work, (i) the driven mechanism of high density plasma coherent structure (i.e., spokes) in the HiPIMS discharge and (ii) how the structure and properties of the TaC/a-C:H and HfC/a-C:H films are regulated by HiPIMS were investigated. For the driven mechanism of spokes, based on the dispersion relationship of HiPIMS plasma and the evolution of the coupling between two azimuthal waves, the coupling-induced wave model was proposed. For the TaC/a-C:H and HfC/a-C:H films, the chemical bond states, structure, morphology, mechanical and tribological properties, thermal stability as well as oxidation resistance of the films were investigated. By comparison with DC deposited films, it is demonstrated that HiPIMS technology provides a potential strategy for preparing higher performance TaC/a-C:H and HfC/a-C:H films in terms of hardness, friction coefficient and wear resistance, oxidation resistance and thermal stability by modulating the chemical bonding state and nanocomposite structure of the films through HiPIMS reactive plasma

This thesis investigated the physical properties of the macrolide antibiotics: Erythromycin dihydrate (EM-DH), Roxithromycin monohydrate (RM-MH) and Azithromycin dihydrate (AZM-DH). The abovementioned hydrate compounds were investigated in terms of the hydrate-anhydrate crystal structure stability, dehydration and observed polymorphism under controlled temperature heating programs. Identified hydrate and anhydrate polymorphs were subjected to physical stability testing during controlled storage. EM-DH was characterized by thermal analysis (DSC, TGA), X-ray diffraction, FTIR and microscopy. Dehydration of EM-DH at temperatures of 100, 157 and 200°C (followed by supercooling to 25°C) produced the form (I) anhydrate (Tm =142.9°C), form (II) anhydrate (Tm = 184.7°C ) and amorph (II) (Tg = 118°C) respectively. The attempts to produce amorph (I) from melting (in vicinity of form (I) melt over temperature range 133°C to 144°C) and supercooling was unsuccessful due to the high crystallization tendency of the form (I) melt. Brief humidity exposure and controlled temperature (40°C)/ humidity storage for 4 days (0-96% RH) revealed hygroscopic behaviour for the anhydrate crystal (forms (I) and (II)) and amorph (II) forms. Form (II) converted to a nonstoichiometric hydrate where extent of water vapour absorption increased with increased storage humidity (2.1% absorbed moisture from recorded TGA at 96% RH). Amorph (II) exhibited similar trends but with greater water absorption of 4.7% (recorded with TGA) at 96% RH. The pulverization and sieving process of amorph (II) (at normal environmental conditions) was accompanied by some water vapour absorption (1.1%). A slightly lower absorbed moisture content of 3.3% (from TGA) after controlled 4 days storage at 40°C/ 96% RH was recorded. This suggested some physical instability (crystallization tendency) of amorph (II) after pulverization. The thermally induced dehydration of RM-MH by DSC-TG was evaluated structurally (SCXRD), morphologically (microscopy) and by kinetic analysis. Various kinetic analysis approaches were employed (advanced, approximation based integral and differential kinetic analysis methods) in order to obtain reliable dehydration kinetic parameters. The crystal structure was little affected by dehydration as most H-bonds were intramolecular and not integral to the crystal structure stability. Kinetic parameters from thermally stimulated dehydration indicated a multidimensional diffusion based mechanism, due to the escape of water from interlinked voids in crystal. The hygroscopicity of the forms RM-MH, Roxithromycin-anhydrate and amorph glass (Tg = 81.4°C) were investigated. Roxithromycinanhydrate (crystalline) converted readily to RM-MH which were found to be compositionally stable over the humidity range 43-96%RH. Amorphous glass exhibited increased water vapour absorption with increasing storage humidity (40°C/ 0-96% RH). TG analysis suggested a moisture content of 3.5% at 96% RH after 4 storage days. DSC and powder XRD analysis of stored pulverised amorphous glass indicated some physical instability due to water induced crystallization. Commercial AZM-DH and its modifications were characterized by thermal analysis (DSC, TGA), SC-XRD and microscopy. Thermally stimulated dehydration of AZM-DH occurred in a two-step process over different temperature ranges. This was attributed to different bonding environments for coordinated waters which were also verified from the crystal structure. Dehydration activation energies for thermally stimulated dehydration were however similar for both loss steps. This was attributed to similarities in the mode of H- bonding. Different forms of AZM were prepared by programmed temperature heating and cooling of AZM-DH. The prepared forms included amorphous glass (melt supercooling), amorphous powder (prepared below crystalline melting temperature), crystalline anhydrate and crystalline partial dehydrate. Humidity exposure indicated hygroscopic behaviour for the amorphous, crystalline anhydrate and crystalline partial dehydrate modifications. Both the crystalline anhydrate and partial dehydrate modifications converted to the stoichiometric dihydrate form (AZM-DH) at normal environmental conditions at ambient temperature. Both the amorph glass and amorph powder exhibited increased moisture absorption with increased humidity exposure. TG analysis of the pulverised amorph glass indicated a moisture content of 5.1% at 96% RH after 4 storage days. The absence of crystalline melt in DSC and presence of Tg (106.9°C) indicated the sample remained amorphous after pulverisation and storage for 4 days at 40°C/ 96% RH.

The subject of the present Ph.D. thesis is constituted by the development and application of innovative modeling techniques for the representation of the thermophysical properties of fluids. The thermophysical properties are divided into thermodynamic properties, related to states of thermodynamic equilibrium and to transformation processes between two equilibrium conditions, and transport properties, concerning systems in a non-uniform state and then affected by transport phenomena; among these, thermal conductivity has been here considered. The knowledge of the thermophysical properties of pure fluids and mixtures is an absolutely crucial need for the design and the optimization of any equipment in the process industry. The thermophysical properties have to be known in dependence on the controlling variables with a precision as high as possible: errors in the values of the required properties can propagate throughout the entire calculation with amplification effects, yielding wrong design and driving away from the optimal operating conditions. The purpose of this thesis work is to set up modeling techniques able to represent the thermophysical properties with a precision comparable with the experimental uncertainty of the experimental measurements of the properties themselves reducing at the same time the required experimental effort. The proposed modeling techniques are based on a heuristic approach, that get the functional representation of a physical dependence directly from a properly organized data base; the effectiveness of the developed heuristic techniques is fundamentally based on the use of the artificial neural network, which have the characteristic of universal function approximators. The development and application of a heuristic modeling technique to produce equations of state (EoS) in the fundamental form for the representation of thermodynamic properties of pure fluids and mixture are presented in the first part of this thesis work. The modeling technique here proposed for the representation of the thermodynamic properties is based on the extended corresponding states (ECS) principle. The basic idea of the ECS model consists in the distortion of the independent variables of the EoS of the reference fluid to transform it into the EoS of the interest fluid. If the simple two-parameter corresponding states principle should work exactly, no tuning distortion would be necessary; since this is not the case, two tuning functions, indicated as shape functions, are then individually required to exactly match the ECS model with a known thermodynamic surface of the interest fluid. The basic requirements of the ECS technique are the fulfillment of a conformality condition between the reference and the target fluid, and the availability of an accurate equation of state in terms of Helmholtz energy for the reference fluid. In the case that either the conformality condition is not verified among the fluids of a same family or no component of the family, whose fluids are supposed to share a conformality condition, disposes of a DEoS, the discussed ECS method cannot in general be effectually applied. In the model proposed in this thesis the ‘correction’ through the variables distortion is performed on a simple EoS representing, even if roughly, the target fluid itself. In other words a simple EoS for the same target fluid is the starting point for the development of a DEoS through the variables distortion, avoiding in this way any problem about the conformality condition fulfillment. It would be then no more necessary to dispose of a ‘reference fluid’, following the classical interpretation of the ECS theory, but rather of only a ‘reference equation’, whose precision is enhanced, or ‘extended’, through the application of the shape functions. Hence the name of extended equation of state (EEoS) chosen to indicate this new modeling method. The shape functions have to be regressed forcing the model to represent known values of experimentally accessible thermodynamic quantities; in the present model their functional formulation is heuristically obtained applying a multilayer feed-forward neural network (MLFN) as universal function approximator. The new approach is constituted by a general fitting procedure in which a mathematical form of the surface has to be ‘spread’ on known values of it and of its derivatives, overcoming the problems presented by the two traditional ECS approaches, i.e., the local solution and the continuous solution. The proposed modeling technique comes from the combination of the EEoS method with the neural networks and then it can be concisely indicated as EEoS-NN model. The EEoS-NN model allows to obtain for the fluid of interest a DEoS in the default fundamental form which allows to calculate any thermodynamic quantity through mathematical derivations only. In order to set up the method and to test its potentialities, data generated from a DEoS for each target fluid are used instead of experimental data, so that the model performances are not hindered by error noise and uneven data distribution. Moving from generated data, the capability of the proposed method has been verified both for pure fluids and for mixtures. A group of pure alkanes, haloalkanes, and strongly polar substances has been considered; the results obtained for these fluids are very promising. The same is valid for the five binary mixtures and two ternary mixtures of haloalkanes here studied. In the case of pure fluids it has been also verified that slightly more than 100 density points evenly distributed in the pressure-density-temperature plane and with low experimental error can be a sufficient input for the model development, allowing to reduce the experimental efforts. The promising performances for the proposed model based on generated data leads to the possibility to reliably develop DEoSs in the EEoS-NN format directly from experimental data. The EEoS-NN technique was then applied to draw DEoSs for the pure fluids sulfur hexafluoride (SF6) and 2-propanol (iC3H8O) directly from the available data sets of the target fluids. The DEoS for SF6 is valid for the liquid, vapor and supercritical region in the ranges from the triple-point temperature at about 223.6 K up to 625 K and for pressures up to 60 MPa, with the exclusion of a region close to the critical point in case of caloric property calculation. The representation of the available experimental data is satisfactory for all the considered properties; in fact the deviations of the equation from the data are comparable with the ascribed uncertainties of the experimental sources. One of the advantages of the EEoS-NN method, shown for the fluid sulfur hexafluoride, is that the data set on which to base the regression procedure can include only density and coexistence values, getting in the meantime a satisfactory performance also for the other properties. The DEoS for iC3H8O is valid for the liquid, vapor and supercritical region for temperatures from 280 up to 600 K and for pressures up to 50 MPa. Due to the substantial lack of data in the near critical region and the non-specialization of this DEoS in representing such region very close to the critical point the present equation is not suggested to be used within a region very close to the critical point. The representation of the available experimental data is satisfactory for all the considered properties; in fact the deviations of the equation from the data are comparable with the realistic uncertainties of the experimental sources for this fluid. The results obtained for the fluid 2-propanol demonstrate that the EEoS-NN modeling method is completely reliable to develop highly effective DEoSs even if the experimental data situation for the fluid is not completely favorable. This aspect is particularly valuable in the case a DEoS is required for engineering applications where the economy of the experimental effort and the representation accuracy have to be met through a suitable compromise. The pointed out features make the EEoS-NN technique a useful tool for the process analysis and optimization. To prove the potential of the cited technique as a tool to study real processes typical of the chemical industry the system propylene + 2-propanol + water has been chosen as an exemplification case. The objective is therefore to investigate the possibility to use the EEoS-NN technique to study the energetic optimization of the extraction process of 2-propanol from aqueous solutions using propylene as solvent. This system has been chosen after a screening of the literature data because it seems to present a favorable phase equilibrium behavior for an extraction operation. Furthermore, the propylene + 2-propanol + water system is thermodynamically strongly deviating from ideal behavior due to several causes as the strong polarity of the components, their association behavior, etc., which increases a lot the difficulties of a complete and accurate thermodynamic representation. For such a reason the set up of a DEoS for this system is an interesting challenge from a scientific point of view, being the first case in which a dedicated equation of state is developed for a strongly deviating ternary mixture. The experimental data available from the literature for the ternary mixture are vapor-liquid equilibrium (VLE) and liquid-liquid equilibrium (LLE). In order to set up a semi-predictive thermodynamic model of the ternary mixture to study its phase behavior, vapor-liquid-liquid equilibrium (VLLE) measurements have been performed. Excess enthalpy measurements have also been carried out for the ternary mixture and for the 2-propanol + water binary mixture in order to obtain a good temperature dependence in the semi-predictive model, constituted of a Peng-Robinson cubic EoS with Wong-Sandler mixing rules and a modified UNIQUAC model to represent the excess Gibbs energy. This model has been used to investigate the phase equilibrium behavior of the ternary mixture from a qualitative point of view. This is a necessary preliminary step to efficiently plan an experimental campaign of measurements suitable to set up a DEoS of the ternary mixture in the EEoS-NN format. The chosen range of interest for the extraction operation is from about 300 to 350 K in temperature, up to 10 MPa in pressure and it extends up to the pure fluids in composition. The properties to be measured in the selected range in order to set up the DEoS are density and phase equilibria. Some isobaric heat capacity measurements are also required to validate the model capability to correctly predict the caloric properties in the range of interest. Density data have been produced using a vibrating tube densimeter (VTD) for the pure 2-propanol, for the propylene + 2-propanol mixture, for the 2-propanol + water mixture and for the propylene + 2-propanol + water mixture. Bubble pressure data were also determined using the VTD for the propylene + 2-propanol mixture and for the propylene + 2-propanol + water mixture. At present the experimental work is still in progress and phase equilibrium and isobaric heat capacity data have to be carried out. This experimental work, together with the development of a DEoS for the propylene + 2-propanol + water mixture, will constitute the extension of this thesis work. Once a thermodynamic model in EEoS-NN format will be obtained, it will be possible to link it with a process simulator, studying the better operative conditions for the 2-propanol extraction process. The development and application of a heuristic modeling technique to produce dedicated equations for the representation of the thermal conductivity of pure fluids is presented in the second part of this thesis work. The proposed model is based on the ECS principle, but the shape functions are got in a continuous analytical form expressed by a universal function approximator, i.e. a neural network, through regression of thermal conductivity data. This innovative approach, named ECS-NN, allows to overcome the problems in obtaining the scale factors presented by the two traditional ECS approaches for transport properties, i.e., the local solution and the continuous solution. The potentiality of the ECS-NN modeling technique for thermal conductivity has been shown with application to both values generated from existing models and experimental values. Assuming R134a as reference fluid, two dedicated thermal conductivity equations have been regressed for carbon dioxide and R152a from the available experimental data. The obtained results are very encouraging; in fact the proposed technique yields thermal conductivity equations that represent the experimental values in the liquid, vapor and supercritical regions within their experimental accuracy; moreover, the method is able to satisfactorily model the strong critical enhancement of thermal conductivity in the near-critical region. The performance change of the model has been studied varying the number of experimental data in the training procedure, showing that about two hundred data points, regularly distributed on the thermal conductivity-temperature-density surface of the target fluid, are sufficient to draw a very precise equation, with evident saving of experimental efforts. Summarizing, the present Ph.D. thesis has shown the effectiveness of the application of heuristic techniques to both thermodynamic and transport property modeling, as a valid alternative to the techniques that are at present adopted. The proposed methods, exploiting the prediction capability of the neural networks, allow to reduce the experimental effort, yielding at the same time equations representing the data within their experimental uncertainties. This feature makes the developed methods suitable tools for the design and optimization of unit operations of the industrial processes.
L’argomento di questa tesi di Dottorato è lo sviluppo e l’applicazione di tecniche modellistiche innovative per la rappresentazione di proprietà termofisiche di fluidi. Le proprietà termofisiche sono divise in proprietà termodinamiche, riguardanti stati di equilibrio termodinamico e processi di trasformazione tra due condizioni di equilibrio, e proprietà di trasporto, riguardanti sistemi in stato non uniforme e quindi caratterizzate da fenomeni di trasporto; tra queste è stata qui trattata la conduttività termica. La conoscenza delle proprietà termofisiche di fluidi puri e miscele è un requisito assolutamente fondamentale nella progettazione ed ottimizzazione di qualsiasi apparecchiatura nell’industria di processo. Le proprietà termofisiche devono essere conosciute in dipendenza delle variabili controllanti con una precisione il più elevata possibile: errori nel valore delle proprietà richieste possono propagarsi attraverso l’intero calcolo amplificandosi, dando luogo ad una progettazione scorretta ed allontanando dalle condizioni operative ottimali. Lo scopo di questa tesi è lo sviluppo di tecniche modellistiche capaci di rappresentare le proprietà termofisiche con un’accuratezza comparabile con l’incertezza sperimentale delle misure stesse, riducendo allo stesso tempo il lavoro sperimentale. Le tecniche modellistiche proposte sono basate su un approccio euristico, che deriva la rappresentazione funzionale di una dipendenza fisica direttamente da una appropriata base di dati; l’efficacia delle tecniche euristiche sviluppate è basata sull’utilizzo delle reti neurali artificiali, che hanno la caratteristica di essere approssimatori universali di funzione. Lo sviluppo e l’applicazione di tecniche modellistiche di natura euristica atte a produrre equazioni di stato (EoS) in forma fondamentale per la rappresentazione delle proprietà termodinamiche di fluidi puri e miscele sono trattati nella prima parte di questa tesi. La tecnica modellistica qui proposta per la rappresentazione delle proprietà termodinamiche è basata sul principio degli stati corrispondenti estesi (ECS). L’idea alla base del modello ECS consiste nella distorsione delle variabili indipendenti della EoS del fluido di riferimento trasformandola nella EoS del fluido di interesse. Se il principio degli stati corrispondenti a due parametri fosse esatto non sarebbero necessari aggiustamenti delle variabili indipendenti, ma poiché questo non è verificato sono richieste due funzioni distorcenti, chiamate shape function, per far corrispondere il modello ECS con una superficie termodinamica nota del fluido d’interesse. Per l’applicazione della tecnica ECS deve essere verificata la condizione di conformality tra il fluido di riferimento ed il fluido target, e l’esistenza di un’accurata equazione di stato espressa in forma di energia libera di Helmholtz per il fluido di riferimento. Nel caso in cui la condizione di conformality tra i fluidi non sia verificata, o nessun fluido della famiglia che si suppone presenti una condizione di conformality con il fluido di interesse disponga di una DEoS, il metodo ECS non può essere applicato efficacemente. Nel modello presentato in questa tesi la ‘correzione’ ottenuta attraverso la distorsione delle variabili è applicata ad un’equazione semplice che rappresenta, anche se approssimativamente, lo stesso fluido target. In altre parole, una EoS semplice per il fluido target stesso è il punto di partenza per lo sviluppo di una DEoS per mezzo della distorsione delle variabili, evitando in questo modo il vincolo costituito dalla necessità di soddisfare la condizione di conformality. Non è più quindi necessario disporre di un ‘fluido di riferimento’, come nell’interpretazione classica della teoria ECS, ma piuttosto solo di una ‘equazione di riferimento’, la cui precisione è aumentata, o ‘estesa’, per mezzo dell’applicazione delle shape function. Di qui deriva il nome di extended equation of state (EEoS) scelto per indicare questa nuova tecnica modellistica. Le shape function devono essere regredite forzando il modello a rappresentare valori noti delle grandezze termodinamiche sperimentalmente accessibili; nel modello proposto la loro forma funzionale è ottenuta in modo euristico utilizzando una multilayer feed-forward neural network (MLFN) come approssimatore universale di funzione. La nuova tecnica è costituita da una procedura di fitting in cui la forma matematica della superficie di deve essere ‘spalmata’ su valori noti della stessa e delle sue derivate, superando i problemi che derivano dai due approcci ECS convenzionali, cioè la local solution e la continuous solution. La tecnica modellistica proposta deriva dalla combinazione del metodo EEoS con le reti neurali ed è quindi brevemente indicata come EEoS-NN. Il modello EEoS-NN permette di ottenere per il fluido di interesse una DEoS in forma fondamentale che consente di calcolare ogni proprietà termodinamica attraverso il solo utilizzo di operazioni di derivazione. Allo scopo di mettere a punto il metodo e di testare le sue potenzialità, sono stati scelti alcuni fluidi target per i quali sono stati utilizzati valori generati da una DEoS preesistente al posto dei dati sperimentali, in modo tale che la performance del modello non sia compromessa dall’error noise e dalla distribuzione irregolare dei dati. Utilizzando dati generati la performance del modello è stata verificata per fluidi puri e per miscele. E’ stato considerato un gruppo di fluidi puri comprendenti alcani, aloalcani, e sostanze fortemente polari; in ogni caso i risultati ottenuti sono molto promettenti. La stessa considerazione può essere fatta per le cinque miscele binarie e le due miscele ternarie di aloalcani studiate. Nel caso di fluidi puri è stato anche verificato che un numero poco superiore a 100 punti di densità regolarmente distribuiti sul piano pressione-densità-temperatura e caratterizzati da un basso errore sperimentale possono essere un input sufficiente per lo sviluppo del modello, permettendo di ridurre il lavoro sperimentale usualmente necessario per l’ottenimento di una DEoS. Le promettenti prestazioni ottenute della tecnica modellistica applicata ai dati generati conducono alla possibilità di mettere a punto delle DEoS in forma EEoS-NN utilizzando direttamente dati sperimentali. La tecnica EEoS-NN è stata quindi utilizzata per produrre la DEoS per i fluidi puri esafluoruro di zolfo (SF6) e 2-propanolo (iC3H8O) direttamente dai dati sperimentali dei due fluidi. La DEoS per il fluido SF6 è valida nel liquido, vapore e supercritico dalla temperatura del punto triplo, a circa 223.6 K, fino a 625 K e per pressioni fino a 60 MPa, con l’esclusione della regione prossima al punto critico nel caso delle proprietà caloriche. La precisione con cui il modello rappresenta i dati è da considerarsi soddisfacente per tutte le proprietà termodinamiche, infatti le deviazioni dell’equazione dai dati sono confrontabili con l’incertezza attribuita alle fonti sperimentali. Uno dei vantaggi del metodo EEoS-NN, evidenziato nell’applicazione al fluido esafluoruro di zolfo, è che la procedura di regressione della DEoS può essere basata su una base dati comprendente solo valori di densità e coesistenza, ottenendo allo stesso tempo una rappresentazione accurata anche delle altre proprietà. La DEoS per il fluido iC3H8O è valida nel liquido, vapore e supercritico per temperature da 280 a 600 K e per pressioni fino a 50 MPa. A causa della mancanza di dati nella regione prossima al punto critico e della non-specializzazione della forma funzionale di questa DEoS nella rappresentazione delle proprietà termodinamiche nelle immediate vicinanze del punto critico l’utilizzo della presente equazione è sconsigliato nella suddetta regione. La rappresentazione delle proprietà termodinamiche è soddisfacente per tutte le proprietà considerate, infatti le deviazioni dell’equazione dai dati sono confrontabili con i valori realisticamente attribuibili alle fonti sperimentali. I risultati ottenuti per il fluido 2-propanolo dimostrano che il metodo modellistico EEoS-NN è completamente affidabile per lo sviluppo di equazioni di stato dedicate anche nella condizione non favorevole in cui i dati sperimentali presentano una scarsa qualità. Questo aspetto è particolarmente importante nel caso in cui una DEoS sia necessaria per applicazioni ingegneristiche, dove deve essere raggiunto un compromesso tra l’economia del lavoro sperimentale e l’accuratezza della rappresentazione delle proprietà termodinamiche. Le caratteristiche evidenziate fanno della tecnica EEoS-NN uno strumento utile per la progettazione e l’ottimizzazione dei processi. Il sistema propilene + 2-propanolo + acqua è stato scelto come caso esemplificativo per provare le potenzialità della tecnica EEoS-NN per l’analisi di processi reali tipici dell’industria chimica. L’obiettivo è perciò indagare la possibilità di utilizzare la tecnica EEoS-NN per studiare l’ottimizzare dal punto di vista energetico del processo di estrazione del fluido 2-propanolo da soluzioni acquose utilizzando il propilene come solvente. Questo sistema è stato scelto dopo uno screening dei dati disponibili in letteratura poiché sembra presentare un andamento degli equilibri di fase adatto per un’operazione di estrazione. Inoltre il sistema propilene + 2-propanolo + acqua presenta un comportamento termodinamico fortemente deviante dall’idealità a causa della forte polarità dei componenti e del loro comportamento associante, aumentando le difficoltà per l’ottenimento di un modello che rappresenti accuratamente le proprietà termodinamiche. Per questo motivo la realizzazione di una DEoS per questo sistema è una sfida interessante dal punto di vista scientifico, infatti esso è il primo caso in cui viene realizzata un’equazione di stato dedicata per una miscela ternaria fortemente deviante. I dati sperimentali disponibili in letteratura per la miscela ternaria sono di equilibrio vapore-liquido (VLE) e di equilibrio liquido-liquido vapore (LLE). Allo scopo di ottenere un modello termodinamico semi-predittivo per la miscela ternaria per studiarne l’equilibrio di fase, sono state effettuate anche misure di equilibrio vapore-liquido-liquido (VLLE). Inoltre, sono state misurate le entalpie di eccesso per la miscela ternaria e per la miscela binaria 2-propanolo + acqua al fine di ottenere una buona rappresentazione della dipendenza dalla temperatura nel modello semi-predittivo, costituito da una EoS cubica di tipo Peng-Robinson, con regole di miscela di tipo Wong-Sandler e un modello UNIQUAC modificato per la rappresentazione della energia libera di Gibbs. Questo modello è stato utilizzato per investigare l’equilibrio di fase della miscela ternaria da un punto di vista qualitativo, step preliminare necessario per pianificare efficientemente una campagna di misure sperimentali adatte ad ottenere una DEoS nel formato EEoS-NN per la miscela. Il range di interesse scelto per il processo di estrazione è circa da 300 a 350 K in temperatura, fino a 10 MPa in pressione e si estende fino ai fluidi puri in composizione. Le proprietà che devono essere misurate in questo range al fine di regredire una DEoS sono densità ed equilibri di fase. Sono inoltre richieste alcune misure di calore specifico a pressione costante per valicare la capacità del modello di rappresentare in modo predittivo le proprietà caloriche nel range di interesse. Il range di interesse per la composizione si estende fino ai fluidi puri. Utilizzando un densimetro a tubo vibrante (VTD) sono state effettuate misure di densità per il fluido puro 2-propanolo, per la miscela propilene + 2-propanolo, per la miscela 2-propanolo + acqua e per la miscela propilene + 2-propanolo + acqua. Ad oggi l’attività sperimentale è ancora in corso, e devono essere effettuate misure di equilibrio di fase e di calore specifico a pressione costante. Questo lavoro sperimentale, insieme alla regressione di una DEoS per la miscela propilene + 2-propanolo + acqua, costituirà il proseguimento di questo lavoro di tesi. Una volta che un modello termodinamico in forma EEoS-NN sarà stato ottenuto, sarà possibile integrarlo in un simulatore di processo, permettendo quindi lo studio delle condizioni operative migliori per il processo di estrazione del fluido 2-propanolo. Lo sviluppo e l’applicazione di tecniche modellistiche di natura euristica atte a produrre equazioni dedicate per la rappresentazione della conduttività termica di fluidi puri sono trattati nella seconda parte di questa tesi. Il modello proposto è basato sul principio ECS, ma le shape functions sono prodotte in una forma analitica continua espressa attraverso un approssimatore universale di funzione, anche in questo caso una rete neurale, attraverso la regressione di dati di conduttività termica. Questo approccio innovativo, denominato ECS-NN, permette di superare i problemi che derivano dai due approcci ECS convenzionali, cioè la local solution e la continuous solution. Le potenzialità della tecnica modellistica ECS-NN per la conduttività termica sono state dimostrate con l’applicazione sia a dati generati da modelli preesistenti, sia a dati sperimentali. Assumendo R134a come fluido di riferimento, sono state ottenute equazioni dedicate di conduttività termica per l’anidride carbonica e per il fluido R152a basate sulle misure sperimentali disponibili in letteratura. I risultati ottenuti sono incoraggianti, infatti la tecnica proposta permette di ottenere equazioni dedicate di conduttività termica che rappresentano i valori sperimentali nelle regioni del liquido, vapore e supercritico con un’accuratezza confrontabile con la loro l’incertezza sperimentale dei dati stessi; inoltre il metodo è adatto alla rappresentazione dell’elevato critical enhancement della superficie di conduttività termica nella regione prossima al punto critico. La variazione della performance del modello è stata studiata variando il numero di dati sperimentali nella procedura di training, mostrando che circa duecento punti, regolarmente distribuiti sulla superficie conduttività termica-temperatura-densità del fluido target, sono sufficienti a ricavare un’equazione molto precisa, con notevole riduzione del lavoro sperimentale. Riassumendo, questa tesi di Dottorato ha mostrato l’efficacia dell’applicazione di tecniche euristiche come valida alternativa alle tecniche attualmente utilizzate per la rappresentazione sia delle proprietà termodinamiche sia delle proprietà di trasporto. I metodo proposti, sfruttando la capacità predittiva delle reti neurali, permettono di ridurre il lavoro sperimentale, producendo allo stesso tempo equazioni in grado di rappresentare i dati con un’accuratezza all’interno della loro incertezza sperimentale. Questa caratteristica fa si che le tecniche sviluppate possano essere considerate strumenti adatti per la progettazione e l’ottimizzazione di operazioni unitarie di processi industriali.

The activation parameters for the temperature dependent irreversible loss of surface-enhanced Raman scattered (SERS) intensity from pyridine and chloride adsorbed at silver surfaces in an electrochemical environment have been determined. Laser-induced heating is introduced as a probe of the chemical nature of SERS-active sites. Surface temperatures are calculated from spectroscopic data. The activation energies associated with the destruction of SERS-active sites at a surface roughened by an illuminated oxidation-reduction cycle (ORC) are 12.8 ± 3.2 kcal/mole and 27.7 ± 3.1 kcal/mole for pyridine at two different types of sites on the Ag surface. Similarly, values for coadsorbed chloride are found to be 11.1 ± 2.4 kcal/mole and 24.5 ± 3.8 kcal/mole. An activation energy of 27.4 ± 1.9 kcal/mole is obtained for pyridine on a silver surface roughened by a nonilluminated ORC. Evidence for the desorption of pyridine and chloride is presented.

In the perspective of manipulating and controlling heat fluxes, graphene represents a promising material revealing an unusually high thermal conductivity �. However, both experimental and theoretical previous works lack of a strict thermal conductivity value, estimating results in the range 89-5000 W m-1 K-1. In this scenario, I address graphene thermal transport properties by means of molecular dynamics simulations using the novel "approach to equilibrium molecular dynamics" (AEMD) technique. The first issue is to offer some insight on the active debate about graphene thermal conductivity extrapolation for infinite sample. To this aim, I perform unbiased (i.e. with no a priori guess) direct atomistic simulations aimed at estimating thermal conductivity in samples with increasing size up to the unprecedented value of 0.1 mm. The results provide evidence that thermal conductivity in graphene is definitely upper limited, in samples long enough to allow a diffusive transport regime for both single and collective phonon excitations. Another important issue is to characterize at atomistic level the experimental techniques used to estimate graphene thermal conductivity. Some of these use laser source to provide heat. For these reasons, I deal with the characterization of the transient response to a pulsed laser focused on a circular graphene sample. In order to reproduce the laser effect on the sample, the K - A01 and

With electronic packaging becoming more complex, simple hand methods to model the thermal performance of the package are insufficient. As computer aided modeling methods came into use, a test system was developed to verify the predictions produced by such modeling methods. The test system is evaluated for operation and performance. Further, the premise of this type of test (the accurate calibration of packaged temperature-sensitive-parameter devices can be done) is investigated using a series of comparative tests. From this information, causes of possible/probable errors in calibration are identified and related to the different methodologies and devices used. Finally, conclusions are presented regarding the further improvement of the test system and methodologies used in this type of testing.

The objectives of this work are to measure phase equilibria in the carbon dioxide + pyrrole system and to correlate and predict the phase behavior of this system with a thermodynamic model. This binary system is of interest due to the growing applications of supercritical carbon dioxide as a solvent or reaction medium for pyrrole. Polypyrrole is an electrically conducting polymer of interest in a number of applications such as anti-static coatings. Pyrrole has also been used as a reactant in enzymatic reaction. Knowledge of the phase behavior of carbon dioxide + pyrrole system is therefore necessary for evaluating optimal conditions and feasibility of such applications. Phase equilibria in the carbon dioxide + pyrrole system were measured at 313 K, 323 K, and 333 K using a synthetic method. Liquid-vapor (LV) phase behavior and liquid-liquid (LL) phase behavior were observed. The pressure in the experiments ranged from 84 to 151.1 bar. The Patel-Teja equation of state and the Mathias-Klotz-Prausnitz mixing rule with two temperature independent parameters was able to correlate the phase equilibrium data satisfactorily and was used to predict the phase behavior at other temperatures. A pressure-temperature diagram was then constructed from these calculations and suggests that the carbon dioxide + pyrrole system exhibit type IV phase behavior in the classification of Scott and van Konynenburg.

Composites, though used in a variety of applications from chairs and office supplies to structures of U.S. Navy ships and aircrafts, are not all designed to hold up to extreme heat flux and high temperature. Fiber-reinforced polymeric composites (FRPC) have been proven to provide the much needed physical and mechanical properties under fire exposure. FRPC notable features are its combination of high specific tensile strength, low weight, along with good corrosion and fatigue resistance. However FRPC are susceptible to thermal degradation and decomposition, which yields flammable gas, and are thus highly combustible. This property restricts polymeric material usage. This study developed a numerical model that simulated the degradation rate and temperature profiles of a fiber-reinforced polyester resin composite exposed to a constant heat flux and hydrocarbon fire in a cone calorimeter. A numerical model is an essential tool because it gives the composite designer the ability to predict results in a time and cost efficient manner. The goal of this thesis is to develop a numerical model to simulate a zonal-layer polyester resin and fiber-glass mat composite and then validate the model with experimental results from a cone calorimeter. By inputting the thermal properties of the layered composite of alternating polymer and polymer-infused glass fiber mat layers, the numerical model is one step closer to representing the experimental data from the cone calorimeter test. The final results are achieved through adding a simulated heat flux from the pilot ignition of the degraded gas of the polyester resin. The results can be coupled into a mechanical model, which may be separately constructed for future study on the mechanical strength of composites under fire conditions.
ID: 030646184; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.M.E.)--University of Central Florida, 2011.; Includes bibliographical references (p. 53-54).
M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Thermo-Fluids Track

Buildings consume more than 30 percent of the primary energy worldwide with 65 percent of this attributed to heating ventilation and cooling. To help address this, stratified concrete panels (SCP) have been developed to provide insulation without compromising the thermal mass of concrete. SCP is created by vibrating a single concrete mix containing heavy and lightweight aggregates. Vibration causes the heavy aggregates drop to the bottom so that two distinct strata are formed; an internal structural/heavyweight layer providing thermal mass and an external lightweight layer for insulation. SCP incorporates waste products, for both financial and environmental gains, from which technical benefits also result. Stratified concrete panels have been made and tested during past research projects with results suggesting that SCP could be a competitive product in the residential construction industry, an area in which precast concrete systems have not been favoured in New Zealand. Consideration has been given to the specific rheological requirements of the concrete mix design and the hardened properties of the finished panels. This research considers the commercial viability of SCP using an industrial setting. For practicality of the setting, some materials were altered from past laboratory work to materials that are more easily sourced and better understood but with similar properties as those used previously. Several panels were cast at Stahlton precast yard in an effort to optimise the production process. Consistent results were not achieved and a range of stratification levels were produced. This showed that some capital investment is required to commercialise SCP to provide more energy for vibration such that sufficient stratification can be reliably attained. Two panels were then stood up in an exposed area with the exterior facing north to test for warping effects in a practical setting. No measurable warping occurred over this time which concurred with past work and long term readings that were taken of four year old panels. Structural, thermal and durability tests were carried out on panels with a range of stratification levels to assess the sensitivity of these properties to the level of stratification. From this it was found that the panels with better stratification had significantly better thermal properties than those with moderate to poor stratification. Generally the thermal targets for this project were not met with the total thermal resistance (R-values) not meeting current code requirements. In some cases structural properties were improved with better stratification as the structural layer was stronger through better consolidation. Delamination potential increased with stratification and with age. This requires further research to minimise this effect using fibres across the layer boundary. Porosity was increased in the structural layer in the poorly to moderately stratified panels as the structural layer was not consolidated enough due to lightweight aggregate contamination. As with any new innovation, market acceptance is largely governed by public perception. With appropriate marketing as a sustainable energy saving product, SCP has the potential to be competitive in the residential construction market with some capital investment.

A novel experimental method to determine the activity of alloy components in very dilute liquid metal solutions has been developed. The method is applied to the measurement of magnesium vapour pressure over nickel alloys to find the thermodynamic properties of magnesium in dilute liquid solutions at 1470°C. The experimental method employs a commercial Atomic Absorption Spectrophotometer to determine directly the vapour pressure of magnesium over the alloys. A radiatively heated Knudsen cell inside a vacuum system contains the metal. Equilibrium constants are given for the reactions, [Formula Omitted] where Al, 0 and Mg are dissolved in liquid nickel. Further, values for the metal-oxygen interaction coefficients [Formula Omitted] and [Formula Omitted] are determined. Finally, a value for the Raoultian activity coefficient at infinite dilution is suggested. A significant change in the activity of magnesium upon the addition of 20% chromium or iron to the dilute liquid nickel alloys was not detected. This is believed due to overpowering magnesium-oxygen interaction at these levels of chromium and iron.
Applied Science, Faculty of
Materials Engineering, Department of
Graduate

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 74-76).
Buildings consume too much energy. For example, 16.6% of all the energy used in the United States goes towards just the heating and cooling of buildings. Many governments, organizations, and companies are setting very ambitious goals to reduce their energy use over the next few years. Because the time periods for these goals are much less than the average lifetime of a building, existing buildings will need to be retrofitted. There are two different types of retrofitting: shallow and deep. Shallow retrofits involve the quickest and least expensive improvements often including reducing infiltration around windows, under doors, etc and blowing more insulation into the attic. Deep retrofits are those that involve costly renovation and typically include adding insulation to the walls and replacing windows. A new, easily installable, inexpensive, and thin insulation would move insulating the walls from the deep retrofit category to the shallow retrofit category and thus would revolutionize the process of retrofitting homes to make them more energy efficient. This thesis provides an overview of a concept for a new, easily installable, inexpensive, thin aerogel-based insulation and goes into detail on how the thermal properties of the aerogel were measured and validated. The transient hot-wire method for measuring the thermal conductivity of very low thermal conductivity silica aerogel (1 0mW/m K at 1 atm) along with a correction for end effects was validated with the NIST (National Institute of Standards and Technology) Standard Reference Material 1459, fumed silica board to within 1 mW/mK. Despite the translucence of the aerogel at certain wavelengths, radiation is not an issue through the aerogel during the hot-wire test but may be an issue in actual use as an insulation. The monolithic aerogel thermal conductivity drops significantly with slightly reduced pressure (3.2 mW/m K at 0.1atm). For the final composite insulation, the new silica aerogel formula is a great choice and it is recommended to reduce the pressure around the aerogel to 1 / 1 0 th. In the future, a prototype of an insulation panel combining a 3-D truss structure, monolithic or granular silica aerogel, and reduced pressure will be constructed and tested.
by Ellann Cohen.
S.M.

Thermal properties of ten different seafood were measured in this research. They included bluefish (Pomatomus saltatrix), croaker (Micropogonias undulatus), spanish mackerel (Scomberomorus maculatus), pink salmon (Oncorhynhus gorbuscha), black seabass (Atractoscion nobilis), spot (Leiostomus xanthurus), shrimp(Pandalus borealis), tilapia (Tilapia aurea), grey sea trout(Cynoscion regalis), and yellow fin tuna (Thunnus albacares) (Wheaton, et al. 1985). Thermal properties measured were thermal conductivity, thermal diffusivity, and specific heat from 5 to 30^oC. Enthalpy was measured from -40 to 30^oC. Moisture and fat content were measured. Thermal conductivity and thermal diffusivity were measured by a rapid transient technique using a bead thermistor probe. Specific heat and enthalpy were measured using a differential scanning calorimeter. Moisture content and fat content were measured by the AOAC specified oven dry method and ether extraction method, respectively. The measured thermal properties agreed well with the scarcely available literature values. They were then statistically correlated with moisture and fat content. Based on statistical analysis, mathematical models relating thermal properties and composition were proposed and compared with the models available in the literature. Models for thermal conductivity and specific heat were recommended to predict these properties of meats and fish with similar composition.
Master of Science

Thesis (Ph. D.) -- University of Maryland, College Park, 2008.
Thesis research directed by: Dept. of Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

In this research, a temperature dependent tribological investigation of selected ternary oxides was undertaken. Based on the promising results of previous studies on silver based ternary oxides, copper based ternary oxides were selected to conduct a comparative study since both copper and silver are located in the same group in the periodic table of the elements. Two methods were used to create ternary oxides: (i) solid chemical synthesis to create powders and (ii) sputtering to produce thin films. X-ray diffraction was used to explore the evolution of phases, chemical properties, and structural properties of the coatings before and after tribotesting. Scanning electron microscopy, Auger scanning nanoprobe spectroscopy, and X-ray photoelectron spectroscopy were used to investigate the chemical and morphological properties of these materials after sliding tests. These techniques revealed that chameleon coatings of copper ternary oxides produce a friction coefficient of 0.23 when wear tested at 430 °C. The low friction is due to the formation of copper tantalate phase and copper in the coatings. All sputtering coatings showed similar tribological properties up to 430 °C.

Low thermal conductivity is a primary limitation in the development of energy-efficient heat transfer fluids that are required in numerous industrial sectors. Recently submicron and high aspect ratio particles (nanoparticles and nanotubes) were introduced into the heat transfer fluids to enhance the thermal conductivity of the resulting nanofluids. The aim of this project was to investigate the physico-chemical properties of nanofluids synthesized using submicron and high aspect ratio particles suspended in heat transfer fluids .

Thesis (Ph.D.)--Mechanical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Graham, Samuel; Committee Co-Chair: Nair, Sankar; Committee Member: Grover - Gallivan, Martha; Committee Member: McDowell, David; Committee Member: Schelling, Patrick; Committee Member: Zhang, Zhuomin

In-situ determination of thermal properties in bedrock is important for the sizing of larger BTES systems. In-situ values of thermal conductivity may reduce required borehole length up to 30%. This thesis treats a new mobile thermal response test equipment (TED), developed in Luleå, Sweden, 1995-98. TED is set up on a small trailer, and is tried out on groundwater filled boreholes, fitted with single and double U-loop piping. It has been used at several commercial borehole direct cooling systems for telephone switching stations in Sweden, and on test-holes in a well documented closed down heat store in Luleå. The response tests show good accuracy and reliability of the measured thermal conductivity and thermal resistance provided good insulation of the equipment. The tests take into account the interaction of the bedrock with the duct piping and filling, the borehole geometry and groundwater and is a valuable tool for pre-investigations for BTES.
Godkänd; 1998; 20070404 (ysko)

One of the major issues facing the coal industry today is the decline in economically recoverable reserves, especially in the Witbank 1 Mpumalanga region of South Africa. This necessitates a critical review of alternate coal sources. One such source was identified as previously discarded and currently arising coal fines. It is well known that great value lies within these fines, but that the high moisture content associated with fine coal leads to thermal inefficiencies, handling problems and increased transport cost. This study will investigate thermal drying as a feasible solution to effectively remove this moisture. During thermal drying coal is fed into a high temperature environment; this can influence the physical and mechanical properties of the coal. The effects include swelling, caking, cracking, loss of water, loss of volatiles, and many more. These effects are investigated by means of thennogravimetric analysis, scanning electron microscopy with a heating stage, proximate analysis and mercury intrusion. Coal samples with an average particle size of 500 um were selected for this study. It was found that: The rate of moisture loss up to temperatures between 150 and 200°C is at a maximum where after the rate declines up to temperatures between 350 and 450°C when primary devolatilisation initiates. No visual changes in the coal are observed up to temperatures between 350 and 450°C. A limited amount of volatiles evolve at a constant rate up to 250°C; this is not significant enough to decrease the calorific value of the coal. Porosity changes in the coal are observed from temperatures as low as 250°C. Thermal drying was found to be a feasible alternative to currently employed drying methods with 150°C selected as the optimal drying temperature. A thermal drying plant is proposed with recommendations for future work needed to realise such a plant.
Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2010

The failure of integrated circuit due to Silicon fracture is one of the problems associated with the production of a semiconductor device. The thermal stresses, which result in die cracking, are for the most part induced during the cooling process after attaching the die with Gold-Silicon solder. Major factors for stress generation in material systems are commonly large temperature gradients and substantial difference in coefficients of thermal expansion.

Evaluation and characterisation of thermal barrier coatings (TBCs) have been conducted correlating microstructure with physical and mechanical properties, to further understand TBC failure mechanisms and performances in this thesis. A modified four-point bending test was employed to investigate the interfacial toughness of atmospheric plasma sprayed TBCs. The delamination of the TBCs occurred mainly within the topcoat. The energy release rate increased from ~50 J/m-2 for as-sprayed conditions to ~120 J/m-2 after annealing at 1150 ºC for 200 hours with a loading phase angle about 42º. Micro X-ray tomography revealed how various types of imperfections developed near the interface and the 3D interface was characterised. Stress measurements by photoluminescence piezospectroscopy (PLPS) and analytical solutions were combined to investigate the local stress around spherically symmetrical portions of a TGO layer formed on Fecralloy. Spherical indenters were used to create curvature with different curvature radii and depths on alloys. The effect of curvature radius on stress was found to be more significant than the depth of local curved area. TGO stress as a function of oxidation time at the curved areas was also discussed. Electron beam physical vapour deposited (EBPVD) TBCs with a β-(Ni,Pt)Al bond coat on CMSX4 substrate were investigated by micro X-ray computed tomography (XCT). The 3D microstructures evolution and damage accumulation were studied. 3D interfacial roughness was calculated and compared to scanning electron microscope image analysis. The calculated interfacial roughness did not change much even after 200 thermal cycles, indicating there was not obvious rumpling in this TBCs sample. Commercial simple and Pt-modified aluminide coatings were studied and compared. Both coatings consisted mainly of β-NiAl phase. Thermogravimetric analysis (TGA) tests indicated that the Pt-modified aluminide coating was much more resistive for oxidation than simple aluminide coating. Instrumented indentation was used to measure the mechanical properties, showing the coatings had similar young’s modulus around 130 GPa while Pt-modified aluminide coating was more ductile and had a higher fracture toughness than simple aluminide coating. The Raman spectra of yttria-stabilised zirconia (YSZ) in the temperature range of 25-1100 ºC were investigated. The peak shift and broadening were carefully analysed. The thermal mismatch stress was found to have a negligible effect on the Raman shift. The dependence can be used to monitor the temperature in YSZ without contact.

We present a periodic technique for measuring the thermal conductivity and diffusivity of thin samples simultaneously. In samples of this type, temperature measurements must be made across the sample faces and are therefore subject to large error due to the interface resistance between the temperature sensor and the sample. The technique uses measurements of the amplitude and phase of the periodic temperature across both a reference sample and the unknown material at several different frequencies. Modeling of the heat flow in the sample allows the simultaneous determination of the thermal parameters of the sample as well as the interface resistance. Data will be presented for standard materials to show the viability of the technique.

Decompositions of solids are typically of the form: A(s) ----> B(s) + gases. Symmetry-controlled routes (based on known and hypothetical crystal structures) for transforming the solid reactant into the solid product were devised as possible decomposition pathways. Lattice energies of the reactants, of the postulated transient intermediate structures and of the final solid products were then estimated by crystal modelling procedures. Profiles of lattice energy changes during the proposed decomposition routes were constructed and any energy barriers were compared with experimental activation energies reported for the thermal decompositions. The crystal modelling was performed with the computer program WMIN. Calculation of the lattice energies involved the development of a model potential for the perfect lattice and the evaluation of the interatomic parameters. The potential was based on the Born model of ionic solids using the Buckingham potential (Ø(r)= Ae⁻r/p - C/r⁶) to describe the short-range energy contribution. Empirical fitting was used to establish reliable interatomic energy parameters. The reliability of the interatomic potentials was assessed by calculating crystal structures and lattice energies (which were not included in the fitting). The particular reactions selected for modelling were the decompositions of the alkaline-earth metal (Ca, Sr, Ba) peroxides and carbonates: M0₂(s) ---> MO(s) + ¹/₂0₂(g) MC0₃(s) ---> MO(s) + CO₂(g)The lattice energies calculated for the known structures were in good agreement with reported values, (except for Ba0₂ and BaC0₃) which provided support for the adequacy of the potential model used. Activation energies calculated for the decomposition of the carbonates were in the correct order but hlgher than experimental values, i. e., 422, 422, 465 and 499 kJ mol̄̄⁻¹ compared to the experimental values of 205, 87(?), 222 and 283 kJ mol̄̄⁻¹ for CaC0₃ (calcite), CaC0₃(aragonite), SrC0₃ and BaC0₃. The values calculated for the peroxides (91 and 100 kJ mol⁻¹ compared to the experimental values of 119 and 185 kJ mol⁻¹ for Sr0₂ and Ba0₂ respectively) were less satisfactory but could be a reflection of the poor structural data used for the peroxides. The significance of this approach to the modelling of solid decompositions is discussed.

In the search of clean and efficient energy sources intermediate temperature solid oxide fuel cells are among the prime candidates. What sets the limit of their efficiency is the solid electrolyte. A promising material for the electrolyte is ceria. This thesis aims to improve the characteristics of these electrolytes and help provide thorough physical understanding of the processes involved. This is realised using first principles calculations. The class of methods based on density functional theory generally ignores temperature effects. To accurately describe the intermediate temperature characteristics I have made adjustments to existing frameworks and developed a qualitatively new method. The new technique, the high temperature effective potential method, is a general theory. The validity is proven on a number of model systems. Other subprojects include low-dimensional segregation effects, adjustments to defect concentration formalism and optimisations of ionic conductivity.

Sorghum is a gluten free cereal and forms the staple diet of a majority of the populations living in the semi-arid tropics dough. It is usually consumed in the form of bread made from the grain flour. Dough made with sorghum flour has poor viscoelastic properties compared to wheat dough and mechanical methods for production of sorghum roti are scarce. This study was conducted to elucidate the rheological and thermal properties of sorghum dough to establish its behavior. The temperature and amount of water used for preparation of the dough and the composition of the flour were varied. Wheat, soya and black gram flours were used to prepare the composite doughs. Sensory characteristics of roti made with these dough samples by the traditional method and mechanical compression were studied. The results are presented and their implications are discussed.

Batters are highly complex systems with wide ranging ingredients including flours, water, flavorings, and spices. Interactions between the ingredients determine the performance of batters and the final quality of coated products. Addition of hydrocolloids into batters of different types of flour provides special effects on batter performance. The functionalities of hydrocolloids-flour mixtures in terms of the thermal and rheological properties of the resulting batter systems were investigated in this study.
The rheological properties of the batter were determined using a strain/stress control rheometer. A steady state method was used to measure the viscosity as a function of the shear rate varying from 0.5 to 150 s-1 at 15°C. The resulting data was then fitted to the Herschel-Bulkley Model. The viscoelastic properties were monitored as a function of temperature and were determined using a dynamic oscillatory test. Two different temperature profiles were used to simulate cooking and storage processes. Differential scanning calorimetry (DSC) was used to determine thermal properties (namely glass transition temperature, gelatinization temperature, ice melting temperature, and enthalpy) and to describe the phase transitions that occur during heating and cooling processes.
The rheological and thermal properties varied for different types of flours and their combination ratios, as well as different types of hydrocolloids at different concentrations. The replacement of corn flour greatly altered the viscosity and viscoelastic properties of wheat based and rice based batter systems. Using 100% corn flour based batter showed highest yield stress, whereas 100% rice flour based batter did not show any yield stress. Higher temperatures and longer times were required to gelatinize starch at the higher levels of rice flour for each batter system flour mix combination. The various combination ratios of the flours apparently did not significant influence the gelatinization temperatures of the batter systems. However they significantly influence the total enthalpies (DeltaHG) of the various samples. Wheat flour based batters showed the lowest glass transition temperatures. Thermal properties of wheat-based batters were influenced by the replacement of wheat with rice or corn flours. Corn flour based batters required considerably more energy for gelatinization during the cooking process.
Hydrocolloids lowered flow behavior index (n) and increased the consistency index (k) of all batters. The gums also changed the onset temperature of structure development and the storage and loss moduli of the batter systems. Hydrocolloids greatly influenced the thermal properties of batter systems. The gums shifted gelatinization temperature and depressed glass transition temperature of resulting batter systems. Further, MC increased the melting temperature (Tm) for the test batter systems as compared with the values for the control system without methylcellulose (MC). Carboxymethylcellulose (CMC) did not show statistically significant effects on the total enthalpies of ice melting for all samples. However, MC and CMC showed more pronounced effects on rice, corn, and their combined flour based batters than it did on wheat flour based batters. However, this characteristic does not show in batter systems containing xanthan gum.

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico
The scientific interest on molecular crystals stems from their great versatility and ease of processing. For pharmaceutically active ingredients, the structure-activity relationship is of major importance. Topiramate, a white and crystalline solid, is a powerful drug efficiently employed to control epilepsy symptoms. The mechanism of action involves a negative modulatory effect on the AMPA/kainate subtypes of glutamate receptors and some types of voltage-gated Na+ and Ca2+ channels, and a positive modulatory effect on some types of GABAA receptors and at least one type of K+ channels in neurons. Despite its pharmacological attributes, the lack of publications regarding its physical-chemical properties in the literature is apparent. In order to fill this gap, a research comprising vibrational spectroscopy techniques (Raman and infrared), thermal analysis (TGA/DTA/DSC), and theoretical calculations, was carried out. With the aid of calculations employing density functional theory (DFT), most of the observed vibrational bands is assigned. Consideration of Raman spectra recorded at temperatures above and below room temperature, as well as under high hydrostatic pressures, indicated maintenance of the orthorhombic crystalline structure under the diverse thermodynamic conditions employed. Thermal analysis, however, showed that, after the melting point, the sample undergoes decomposition in a process comprising three stages, possibly initiated with loss of the sulfamate group by the molecule. This event inspired a theoretical study aimed at promoting the sulfamate group bond breakage in a controlled way by employing a laser instead of heat. This was accomplished by quantum dynamics simulations which showed that, by using a set of ultrashort pulses in the infrared region, it is possible to reach levels close to 70 % dissociation in less than 3 ps.
O interesse cientÃfico pelos cristais moleculares resulta da facilidade de processamento destes materiais, e de sua grande versatilidade. No caso de drogas, a relaÃÃo entre estrutura e atividade à de suma importÃncia. Topiramato, um sÃlido branco e cristalino, à um fÃrmaco utilizado com bastante eficiÃncia para controlar os sintomas da epilepsia. O mecanismo de aÃÃo envolve um efeito modulatÃrio negativo nos receptores de glutamato do subtipo AMPA/kainato e alguns tipos de canais de Na+ e Ca2+ voltagem-dependentes, bem como um efeito modulatÃrio positivo em alguns tipos de receptores GABAA e pelo menos um tipo de canal de K+ nos neurÃnios. A despeito de suas qualidades farmacolÃgicas, a escassez de trabalhos relacionados Ãs suas propriedades fÃsico-quÃmicas na literatura à evidente. Para ajudar a preencher esta lacuna, uma investigaÃÃo envolvendo tÃcnicas de espectroscopia vibracional (Raman e infravermelho), anÃlises tÃrmicas (TGA/DTA/DSC), e cÃlculos teÃricos, foi realizada. Com a ajuda de cÃlculos empregando a teoria do funcional de densidade (DFT), a atribuiÃÃo da maioria das bandas vibracionais observadas foi realizada. A observaÃÃo dos espectros Raman obtidos em temperaturas acima e abaixo da ambiente, bem como sob altas pressÃes hidrostÃticas, indicou que a estrutura cristalina ortorrÃmbica à mantida nas diferentes condiÃÃes termodinÃmicas empregadas. A anÃlise tÃrmica, entretanto, mostrou que, apÃs a fusÃo, o material sofre decomposiÃÃo em um processo que envolve trÃs etapas, possivelmente iniciado com a perda do grupo sulfamato pela molÃcula. Este fato motivou um estudo teÃrico a fim de modelar a quebra da ligaÃÃo do sulfamato de maneira controlada, utilizando um laser em lugar de calor. Isto foi realizado com simulaÃÃes de dinÃmica quÃntica, que mostraram que, atravÃs da utilizaÃÃo de uma combinaÃÃo de pulsos ultracurtos na regiÃo do infravermelho, à possÃvel atingir nÃveis prÃximos a 70% de dissociaÃÃo em menos de 3 ps.