Os materiais poliméricos são vastamente utilizados em várias áreas de aplicação, como na construção civil, automobilística, embalagens, indústrias em geral, entre outras, substituindo de modo versátil e eficiente os metais, cerâmicos e madeira. No entanto, existe um grande volume de descarte de resíduos industriais poliméricos que atualmente não recebem destinação adequada para reciclagem, entre eles o poliuretano (PU) termorrígido (espumas rígidas e flexíveis). O PU é um material versátil devido a sua vasta possibilidade de aplicações, porém grandes volumes de PU na forma de resíduos industriais e materiais de pós-uso são descartados em aterros industriais e sanitários todos os anos. O reaproveitamento dos resíduos de PU pelo processo de reciclagem mecânica é uma alternativa ambientalmente sustentável e correta, pois gera valor agregado a este material e promove uma melhor utilização dos recursos naturais não renováveis. O objetivo deste trabalho foi o desenvolvimento de placas aglomeradas de resíduos industriais de poliuretano skin (PUs) com a adição de diferentes retardantes de chama, além da avaliação das propriedades de reação ao fogo, morfológicas, físicas e mecânicas dos aglomerados obtidos. As composições utilizadas foram 40 a 70 % (massa) de resíduos industriais de PUs, 30 % de agente aglomerante (Elastan) e 0 a 30 % de diferentes retardantes de chama (alumina trihidratada - ATH, polifosfato de melamina - MPP, polifosfato de amônio - APP e trióxido de antimônio + óxido de decabromodifenila - TADB ). Para obtenção das placas aglomeradas, diferentes composições foram moldadas por compressão utilizando 2 a 6 kgf·cm-2 a 60 ºC por 10 min. Este estudo concluiu que as amostras PUs(40)/APP(30) e PUs(40)/TADB(30) (contendo 30 % (massa) de retardantes de chama) apresentaram os melhores resultados de reação ao fogo, com classificação V0 conforme a norma UL94-V. Foi evidenciado também que diferentes tamanhos de granulometrias de PUs não alteraram as propriedades de comportamento ao fogo dos aglomerados desenvolvidos. Os ensaios mecânicos mostraram que os aglomerados possuem resistência superior à necessária para o manuseio e aplicação dos mesmos, e os resultados de condutividade térmica mostraram que estes materiais possivelmente podem ser destinados para aplicações térmicas na construção civil e na indústria. / The polymeric materials are widely used in many application areas, such as in civil construction, automotive, packaging, general industry, among others, replacing metals, ceramics and wood in a versatile and efficient way However, there is a large volume of discard of polymeric industrial waste that does not currently receive adequate destination for recycling, among them thermo-rigid polyurethane (PU) (rigid and flexible foams). The polyurethane (PU) is a versatile material because of its wide range of applications, but large volumes of PU in the form of industrial waste and post-use materials are disposed of in industrial and sanitary landfills every year. The reuse of PU waste by the mechanical recycling process is an environmentally sustainable and correct alternative, as it generates added value to this material and promotes a better use of non-renewable natural resources. The objective of this work was the development of agglomerated boards of skin polyurethane (PUs) (industrial wast) with the addition of different flame retardants, as well as the evaluation of fire reaction, morphological, physical and mechanical properties of the agglomerates obtained. The compositions used were 40 to 70 % (mass) industrial waste PUs, 30 % binder agent (Elastan) and 0 to 30 % of different flame retardants (alumina trihydrate - ATH, melamine polyphosphate - MPP, ammonium polyphosphate - APP and antimony trioxide + decabromodiphenyl oxide - TADB). To obtain the agglomerated boards, different compositions were compression molded using 2 to 6 kgf·cm-2 at 60 °C for 10 min. This study concluded that the samples PUs(40)/APP(30) and PUs(40)/TADB(30) (containing 30 % by mass of flame retardants) presented the best results of reaction to fire, with classification V0, according to the UL94-V standard. It was also evidenced that different size of PU granulometry does not alter the properties of reaction to fire of the developed agglomerates. The mechanical tests show that the agglomerates have superior resistance than necessary for the handling and application, and the results of thermal conductivity prove that these materials can possibly be destined for thermic applications in building construction and industry.

D. Ing. / Power electronics refers to electronic processing of electrical power. In this process the electrical power is controlled by switching of power semiconductor devices as well as electromagnetically stored in electrical and magnetic fields while the energy flow is directed through selective conduction paths. The losses/power-efficiency of all these actions is of paramount importance in the processing. The lack for standardisation and the absence of a modular approach is a barrier to the development of more compact systems. Recently more research resources have been invested in development of integrated power electronic modules as an attempt to solve this problem. By integrating power electronic components, an increase in the power density is achieved, which unfortunately also leads to higher internal heat-generation and higher operating temperatures. This has an unfavourable effect on electronic behaviour and the reliability of the structures. In order to maintain the advances made in volume reduction of integrated power electronics, efficient and cost effective methods for removing heat is of essence. In this investigation the performance of rectangular cross-section embedded solid-state heatextraction inserts to increase thermal heat spreading and the reduction of steady-state peak temperatures was evaluated theoretically and experimentally. Theoretically, the cross sectional aspect ratio of such inserts was thermally optimised for a wide range of dimensional, thermal, and material property conditions. Possible materials investigated for use as heat extractors in power electronics include aluminium nitride, beryllium oxide, and synthetic diamond. The presence of interfacial thermal resistance was theoretically found to have a significant detrimental influence on the thermal performance of an integrated heat-extraction system and should be minimised as far as possible. For conditions commonly found in integrated power passives, continuous embedded heatextraction layers are proposed. Theoretically it is shown that such inserts can aid in the increase of power density by reducing the temperature increase per unit volume of heat-generation. Experimental test results corresponded closely with the theoretically expected allowed increase in heat-generation that could be accommodated due to the heat-extraction action of the inserts. As an experimental system, insertion of aluminium nitride into ferrite in an integrated electromagnetic power passive module was investigated. An increase of 187% in the effective power density could be achieved due to the presence of aluminium nitride heat-extraction layers embedded into ferrite. Preliminary magnetic flux density optimisation, in terms of the volume fraction occupied by a parallel-layered heat-extraction system, was performed for a wide range of heat-extraction materials, and interfacial resistance values.

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / In this paper, a three-dimensional bending solution of doubly-curved shells subjected to mechanical, thermal and hygrothermal load is studied. Through-the-thickness temperature of the shell is modeled by Fourier's heat conduction equation. Fick's moisture diffusion law equation is used to determine the hygro-thermal profile through-the-thickness. The partial differential equations are solved by using the Navier closed form summations which are valid only for shells with constant radii of curvature among the midsurface and with simply supported boundary conditions on its shell's edges. The shell governing equations are solved by discretizing the thickness profile via Legendre's grid distribution and by using the Differential Quadrature Method (DQM). The Layerwise capabilities of the method is guaranteed by imposing the inter-laminar continuity of out-of-the-plane stresses, displacements, temperature and hygrothermal load thickness profile. The zero-stress condition for the transverse shear stresses is imposed due to the fact that no mechanical loads are applied in those directions. Results for cylindrical, spherical panels and rectangular plates are presented. Comparisons are made with Layerwise and three-dimensional solutions available in literature. The results have strong accuracy and a benchmark problem is delivered. / Consejo Nacional de Ciencia, Tecnología e Innovación Tecnológica

A method of performing local transient heat flux measurements in an uncooled axisymmetric hybrid rocket nozzle is presented. Surface temperatures are collected at various axial locations during short duration tests and post processed using finite difference techniques to determine local transient heat fluxes and film coefficients. Comparisons are made between the collected data and the complete Bartz model. Although strong agreement is observed in certain sections of the nozzle, ideal steady state conditions are not observed to entirely validate the Bartz model for hybrid rocket nozzles. An experimental error analysis indicates the experimental heat fluxes are accurate within ±5.2% and supports the accuracy of the results.

No description available.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN. / Bibliography: leaves 99-110. / by David Samuel Goldberg. / M.S.

The thermal conductivities of polystyrene in benzene solutions at concentrations of 0.l to 15 weight percent were measured at 25° C and atmospheric pressure. Osmotic pressure measurements and information supplied by the manufacturer indicated number average molecular weights (M̅_N) of 21,000, 264,000, and 660,000 for the three polystyrene polymers studied. The following equation was obtained by regression analysis of the results and predicts the measured thermal conductivity within ± 2 percent in the range of variables studied. K = 0.1088 - 0.1311 C + 0.57629 C² - 6.40 x 10⁻⁵ (M̅_N x 10⁻⁵)² - 4.2 x 10⁻³ C(M̅_N x 10⁻⁵) where: K = thermal conductivity of solution, Btu/hr-ft-°F C = weight fraction polymer M̅_N = number average molecular weight The conductivities were measured in a steady-state concentric cylinder apparatus developed for measuring the thermal conductivity of viscous liquids. The annular gap was 0.052 inches and guard heaters were employed to minimize end losses and distortion of the steady-state temperature distribution at the ends. The apparatus was calibrated with three liquids of known thermal conductivity, water, cyclohexanol and ethylene glycol. The calibration factor was found to be constant to within experimental error (± 3 percent) over the range of measurements. / Master of Science

<p> This study focuses on developing a new online recursive numerical algorithm for a coupled nonlinear inverse heat conduction-microstructure problem. This algorithm is essential in identifying, designing and controlling many industrial applications such as the quenching process for heat treating of materials, chemical vapor deposition and industrial baking. In order to develop the above algorithm, a systematic four stage research plan has been conducted. </P> <p> The first and second stages were devoted to thoroughly reviewing the existing inverse heat conduction techniques. Unlike most inverse heat conduction solution methods that are batch form techniques, the online input estimation algorithm can be used for controlling the process in real time. Therefore, in the first stage, the effect of different parameters of the online input estimation algorithm on the estimate bias has been investigated. These parameters are the stabilizing parameter, the measurement errors standard deviation, the temporal step size, the spatial step size, the location of the thermocouple as well as the initial assumption of the state error covariance and error covariance of the input estimate. Furthermore, three different discretization schemes; namely: explicit, implicit and Crank-Nicholson have been employed in the input estimation algorithm to evaluate their effect on the algorithm performance. </p> <p> The effect of changing the stabilizing parameter has been investigated using three different forms of boundary conditions covering most practical boundary heat flux conditions. These cases are: square, triangular and mixed function heat fluxes. The most important finding of this investigation is that a robust range of the stabilizing parameter has been found which achieves the desired trade-off between the filter tracking ability and its sensitivity to measurement errors. For the three considered cases, it has been found that there is a common optimal value of the stabilizing parameter at which the estimate bias is minimal. This finding is important for practical applications since this parameter is usually unknown. Therefore, this study provides a needed guidance for assuming this parameter. </p> <p> In stage three of this study, a new, more efficient direct numerical algorithm has been developed to predict the thermal and microstructure fields during quenching of steel rods. The present algorithm solves the full nonlinear heat conduction equation using a central finite-difference scheme coupled with a fourth-order Runge-Kutta nonlinear solver. Numerical results obtained using the present algorithm have been validated using experimental data and numerical results available in the literature. In addition to its accurate predictions, the present algorithm does not require iterations; hence, it is computationally more efficient than previous numerical algorithms. </p> <p> The work performed in stage four of this research focused on developing and applying an inverse algorithm to estimate the surface temperatures and surface heat flux of a steel cylinder during the quenching process. The conventional online input estimation algorithm has been modified and used for the first time to handle this coupled nonlinear problem. The nonlinearity of the problem has been treated explicitly which resulted in a non-iterative algorithm suitable for real-time control of the quenching process. The obtained results have been validated using experimental data and numerical results obtained by solving the direct problem using the direct solver developed in stage three of this work. These results showed that the algorithm is efficiently reconstructing the shape of the convective surface heat flux. </p> / Thesis / Doctor of Philosophy (PhD)

The boundary element method (BEM) has become a powerful method for the numerical solution of boundary-value problems (BVPs), due to its ability (at least for problems with constant coefficients) of reducing a BVP for a linear partial differential equation (PDE) defined in a domain to an integral equation defined on the boundary, leading to a simplified discretisation process with boundary elements only. On the other hand, the coefficients in the mathematical model of a physical problem typically correspond to the material parameters of the problem. In many physical problems, the governing equation is likely to involve variable coefficients. The application of the BEM to these equations is hampered by the difficulty of finding a fundamental solution. The first part of this thesis will focus on the derivation of the boundary integral equation (BIE) for the Laplace equation, and numerical results are presented for some examples using constant elements. Then, the formulations of the boundary-domain integral or integro-differential equation (BDIE or BDIDE) for heat conduction problems with variable coefficients are presented using a parametrix (Levi function), which is usually available. The second part of this thesis deals with the extension of the BDIE and BDIDE formulations to the treatment of the two-dimensional Helmholtz equation with variable coefficients. Four possible cases are investigated, first of all when both material parameters and wave number are constant, in which case the zero-order Bessel function of the second kind is used as fundamental solution. Moreover, when the material parameters are variable (with constant or variable wave number), a parametrix is adopted to reduce the Helmholtz equation to a BDIE or a BDIDE. Finally, when material parameters are constant (with variable wave number), the standard fundamental solution for the Laplace equation is used in the formulation. In the third part, the radial integration method (RIM) is introduced and discussed in detail. Modifications are introduced to the RIM, particularly the fact that the radial integral is calculated by using a pure boundary-only integral which relaxes the “star-shaped” requirement of the RIM. Then, the RIM is used to convert the domain integrals appearing in both BDIE and BDIDE for heat conduction and Helmholtz equations to equivalent boundary integrals. For domain integrals consisting of known functions the transformation is straightforward, while for domain integrals that include unknown variables the transformation is accomplished with the use of augmented radial basis functions (RBFs). The most attractive feature of the method is that the transformations are very simple and have similar forms for both 2D and 3D problems. Finally, the application of the RIM is discussed for the diffusion equation, in which the parabolic PDE is initially reformulated as a BDIE or a BDIDE and the RIM is used to convert the resulting domain integrals to equivalent boundary integrals. Three cases have been investigated, for homogenous, non-homogeneous and variable coefficient diffusion problems.

Lau Kin Wing. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 80-83). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.3 / Chapter 1.1 --- Heat conduction problem --- p.3 / Chapter 1.2 --- Direct problem --- p.4 / Chapter 1.3 --- Inverse problem --- p.4 / Chapter 1.4 --- Difficulty of the inverse problems --- p.5 / Chapter 1.5 --- A simple but important example for instability --- p.5 / Chapter 1.6 --- The purpose of this thesis --- p.7 / Chapter 2 --- Stability of the inverse problem --- p.9 / Chapter 2.1 --- Conditional stability results --- p.9 / Chapter 2.2 --- Stability of the inverse problems --- p.11 / Chapter 3 --- The continuous formulation --- p.30 / Chapter 3.1 --- Constrained minimization problem --- p.30 / Chapter 3.2 --- Existence of minimizers to the minimization problem --- p.31 / Chapter 4 --- Discretization and its convergence --- p.36 / Chapter 4.1 --- Finite element space --- p.36 / Chapter 4.2 --- Two important discrete projection operators --- p.37 / Chapter 4.3 --- Finite element problem --- p.39 / Chapter 4.4 --- Existence of minimizers to the finite element problem --- p.39 / Chapter 4.5 --- Discrete minimizers and global minimizers --- p.42 / Chapter 5 --- Numerical algorithms --- p.51 / Chapter 5.1 --- Gateaux derivative --- p.51 / Chapter 5.2 --- Nonlinear single-grid gradient method --- p.53 / Chapter 5.3 --- Nonlinear multigrid gradient method --- p.55 / Chapter 6 --- Numerical experiments --- p.60 / Chapter 6.1 --- One dimensional examples --- p.60 / Chapter 6.2 --- Two dimensional examples --- p.66