Made available in DSpace on 2014-10-09T12:24:39Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:16Z (GMT). No. of bitstreams: 1 00287.pdf: 1122753 bytes, checksum: a978ff8816ae53f9979ce18a70a88cb2 (MD5) / Dissertacao (Mestrado) / IEA/D / Escola Politecnica, Universidade de Sao Paulo - POLI/USP

Orientador: Marcelo Moreira Ganzarolli / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-20T13:22:43Z (GMT). No. of bitstreams: 1 Simoes_RobertoMac-Intyer_M.pdf: 2139090 bytes, checksum: 0d40eb0587d86506df37c76ba2e02031 (MD5) Previous issue date: 2011 / Resumo: Realizou-se uma análise experimental para estudar a transferência de calor conjugada convecção natural-condução em um canal vertical de placas paralelas contendo aquecedores bidimensionais protuberantes discretos distribuídos uniformemente sobre a superfície de uma das placas (substrato condutivo). O objetivo é prever a distribuição de sobretemperatura local nos elementos protuberantes em um aquecimento não uniforme, baseada nas medições dos elementos da matriz da função de Green discreta inversa, chamados de coeficientes de influência conjugados. O método de superposição linear foi utilizado sob a condição de que o efeito do empuxo local é insignificante comparado com o escoamento global induzido ao longo do canal. O canal é composto de uma placa de epóxi de 0,0016 m de espessura, com sete fontes de calor protuberantes de alumínio polido montadas em sua superfície, e uma placa adiabática lisa na parede oposta. O canal tem 0,365 m de altura e 0,340 m de largura. Na análise experimental, os espaçamentos entre as paredes do canal utilizados foram b=20mm e b=30mm. A máxima potência global imposta no canal foi 70W. Os coeficientes de influência conjugados foram determinados a partir dos perfis de sobretemperaturas obtidos a partir de experimentos de aquecimento uniforme e experimentos com um elemento desligado. Esses coeficientes, em diferentes níveis de potência, foram utilizados para comparar os perfis de sobretemperatura experimentais e os perfis preditos pelo método da função de Green discreta inversa. A aplicação desta metodologia para o problema de transferência de calor conjugado por convecção naturalcondução fornece uma predição razoável da distribuição de sobretemperatura para uma dissipação de potência arbitrária nos elementos protuberantes / Abstract: An experimental analysis was performed to study conjugate natural convection-conduction heat transfer in a vertical parallel plate channel containing discrete and protruding twodimensional heaters distributed uniformly on the surface of one of the plates (conductive substrate). The objective is to predict the local overtemperature distribution in the protruding elements by nonuniform heating, based on measurements of the inverse discrete Green's function matrix elements, called conjugate influence coefficients. The linear superposition method was used, assuming the condition of negligible local buoyancy effect compared to the global flow induced throughout the channel. The channel is composed of an epoxy plate 0.0016 m thick, with seven protruding heat sources of polished aluminum mounted on its surface, and an adiabatic smooth plate on the opposite wall. The channel is 0.365 m long and 0.34 m wide, with channel wall to wall spacing of 0.02 m. In the experimental analysis, the spacing between the channel walls utilized was b=0.020m and b=30mm. The maximum global power imposed on the channel was 70W. The conjugate influence coefficients were determined from the overtemperatures profiles obtained from the uniform heating experiments and the no-power experiments. These coefficients, at different power levels, were utilized to compare the experimental overtemperature profiles and the overtemperature profiles predited by the inverse discrete Green's function method. The application of this methodology for the conjugate natural convection-conduction heat transfer problem provided a reasonable prediction of overtemperature distribution for arbitrary power dissipation in the protruding elements / Mestrado / Termica e Fluidos / Mestre em Engenharia Mecânica

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Includes bibliographical references. / This thesis is concerned with the numerical modelling of the transient nonlinear heat conduction problem in solid continua. The hyperbolic governing equation is specialised to a parabolic equation which is sufficient for most engineering applications. The theoretical development includes the effects of conduction, specific heat, internal heat generation and the boundary conditions of convection, radiation, specified temperatures and flux, as well as point sources in the domain. The finite element spatial semidiscretisation of the equations is formally derived from the weak form of the governing equations. Temporal discretisation is obtained through an implicit/explicit difference scheme. The material properties are allowed to be temperature dependent, and consequently a modified Newton-Raphson iterative scheme is employed to solve the equations. The fully discretised equations are solved by implementing the algorithm in an existing finite element stress analysis code. Modelling is possible using four or eight-noded isoparametric elements, and solution control is possible through choice of time step size and choice of time integration method. Five examples are employed to demonstrate the ability of the program. The results compare well with published analytical solutions.

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This study presents the numerical analysis of steady laminar flow heat transfer in a horizontal rectangular duct with differential heating on the vertical walls. Three heating configurations: one uniform wall temperature (CS1) and two linearly varying wall temperature cases (CS2 and CS3) are analysed. The study considers the combined effects of natural convection, forced convection and radiation heat transfer on the overall heat transfer characteristics. Air, which is assumed to be a non-participating medium, is chosen as the working fluid. A computational fluid dynamics solver is used to solve a set of governing equations for a range of parameters.For chosen duct aspect ratios, the numerical model simulates the flow and heat transfer for two main effects: buoyancy and radiation heat transfer. Buoyancy effect is represented by Grashof number, which is varied from 2,000 to 1,000,000. The effect of radiation heat transfer is examined by choosing different wall surface emissivity values. The weak and strong radiation effect is represented by the emissivity values of 0.05 and 0.85 respectively. Three duct aspect ratios are considered - 0.5, 1 and 2. The heat transfer characteristics of all the above heating configurations - CS1, CS2, and CS3 are analysed and compared. The numerical results show that, for all heating configurations and duct aspect ratios, the overall heat transfer rate is enhanced when the buoyancy effect increases. Since buoyancy effect induces natural circulation, this circulation is therefore the main mechanism that enhances heat transfer. Radiation heat transfer is found to significantly influence convection heat transfer in high Grashof numbers.

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<p>In gas quenching, metal parts are rapidly cooled from hightemperatures, and the convection heat transfer coefficientdistributions are of importance for the hardness and thedistortion (the shape nonuniformities) of the quenched parts.Thermochromic liquid crystals (TLC) and a thin foil techniques,were investi- gated and used for studies of a circular cylinderin axial flows, affected and not affected by upstream owmodifying inserts. Quadratic prisms in cross ows were alsostudied, a single prism, two prisms arranged in-line, and forfour prisms arranged in a square pattern. In this study,particle image velocime- try (PIV) was used for visualizationof the flow, giving physical insight to the convection heattransfer data. Further, relations of the type<i>Nu</i>=<i>CRe</i><i>e</i>were established. The TLC and thin foil techniques werealso used to indicate the dimensions of separated flowregions.</p><p><b>Descriptors:</b>Fluid mechanics, wind-tunnel, turbulence,gas quenching, con- vection heat transfer, thermochromic liquidcrystals, calibration, temperature measurement errors, thinfoils, particle image velocimetry, cylinder in axial flow, flowmodifying inserts, quadratic prisms in cross flow</p>

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