Thermoelectric generators (TEGs) are currently being explored for their potential in harvesting energy from automobile exhaust. TEGs in form of an appropriate TEG- Heat exchanger module can utilize the temperature difference between the hot exhaust gases and the automobile coolant and convert it into electrical voltage. The amount of power is anticipated to be a few hundred watts depending on the temperature gradient and the material of the TEGs. The focus of this study is increasing the hot side heat transfer for improved performance of the thermoelectric generators using two different internal fins — louvered fins and herringbone wavy fins. The multi-louvered fins basically have 'multi flat plate' behavior and will enhance the heat transfer by deflecting the air from its original path and aligning it with the plane of the louvers. Herringbone fins are used to lengthen the path of airflow allowing for greater residence time and better mixing of the flow. They also provide for greater wetted surface area achieving higher heat transfer. The flow and heat transfer behavior inside the exhaust pipe test section with internal fins is modeled using commercial numerical software. The thermal and flow behavior through both these internal fins depends to a large extent on geometric parameters and fin arrangement. Optimization of the fin design is considered to determine the configuration that provides highest heat transfer while providing least pressure drop across the pipe length. The heat transfer and pressure drop characteristics are compared to the baseline flow without any fin enhancement. / Master of Science

A presente pesquisa trata do estudo teórico/experimental dos efeitos da geometria e dos parâmetros construtivos em trocadores de calor compactos do tipo serpentina para aplicações em refrigeração e ar condicionado no desempenho termo/hidráulico do ar. Para tanto, 15 serpentinas comerciais foram submetidas a testes em uma bancada experimental onde ambas as condições de entrada do ar e da água quente, utilizada como fluido dos tubos, podiam ser controladas e ajustadas. Serpentinas com aletas corrugadas (\"wavy\") e ventiladas convexas (\"convex louver\"), com distintas densidades de atletas, número de fileiras de tubos em profundidade, diâmetro e passo de tubos foram investigadas. Um programa de simulação de serpentinas foi desenvolvido para dar suporte ao tratamento de resultados. Os resultados experimentais obtidos confirmaram tendências da literatura acerca de efeitos da geometria da serpentina no desempenho termo/hidráulico do ar nas serpentinas. Algumas correlações da literatura se compararam bem aos resultados experimentais, embora algumas ilustraram importantes discrepâncias. Foram também investigadas distintas configurações geométricas segundo uma análise que envolve a segunda lei da Termodinâmica. Finalmente, os resultados experimentais, mediante regressão de dados, permitiram a elaboração de correlações gerais para os coeficientes de transferência de calor e de atrito do ar que incorporam os efeitos dos parâmetros geométricos das serpentinas. Tais correlações representaram bem os resultados experimentais com razoável acuracidade. / The research reported herein is about a theoretical and experimental study of the effects of geometric and constructive parameters of compact heat exchangers of the coil type for refrigeration and air conditioning applications over the air-side thermo-hydraulic performance. For that purpose, 15 commercial coils have been submitted to tests in an experimental set-up where both the inlet conditions of the air and those of the warm water, used as tube fluid, could be adequately controlled and adjusted. Wavy and convex louver fin coils with different fin density, number of tube rows, and tube spacing and diameter have been investigated. A computer simulation program of air coils has been developed as a working tool in the experimental results treatment and manipulation. The obtained experimental results follow closely established trends of the literature regarding the effects of the geometric parameters over the thermo-hydraulic performance of the air flow in the coils. Some correlations from the literature compare reasonably well with the experimental results though some have shown important discrepancies. It has also been investigated the performance of the different geometric configurations through a second law of Thermodynamics analysis. Finally, experimental results have been curve fitted in such a way to develop generalized correlations for the air-side heat transfer and friction coefficients that include all the important geometric parameters of the aircoils. Such correlations have proved to fit the experimental results with reasonable accuracy.

A presente pesquisa trata do estudo teórico/experimental dos efeitos da geometria e dos parâmetros construtivos em trocadores de calor compactos do tipo serpentina para aplicações em refrigeração e ar condicionado no desempenho termo/hidráulico do ar. Para tanto, 15 serpentinas comerciais foram submetidas a testes em uma bancada experimental onde ambas as condições de entrada do ar e da água quente, utilizada como fluido dos tubos, podiam ser controladas e ajustadas. Serpentinas com aletas corrugadas (\"wavy\") e ventiladas convexas (\"convex louver\"), com distintas densidades de atletas, número de fileiras de tubos em profundidade, diâmetro e passo de tubos foram investigadas. Um programa de simulação de serpentinas foi desenvolvido para dar suporte ao tratamento de resultados. Os resultados experimentais obtidos confirmaram tendências da literatura acerca de efeitos da geometria da serpentina no desempenho termo/hidráulico do ar nas serpentinas. Algumas correlações da literatura se compararam bem aos resultados experimentais, embora algumas ilustraram importantes discrepâncias. Foram também investigadas distintas configurações geométricas segundo uma análise que envolve a segunda lei da Termodinâmica. Finalmente, os resultados experimentais, mediante regressão de dados, permitiram a elaboração de correlações gerais para os coeficientes de transferência de calor e de atrito do ar que incorporam os efeitos dos parâmetros geométricos das serpentinas. Tais correlações representaram bem os resultados experimentais com razoável acuracidade. / The research reported herein is about a theoretical and experimental study of the effects of geometric and constructive parameters of compact heat exchangers of the coil type for refrigeration and air conditioning applications over the air-side thermo-hydraulic performance. For that purpose, 15 commercial coils have been submitted to tests in an experimental set-up where both the inlet conditions of the air and those of the warm water, used as tube fluid, could be adequately controlled and adjusted. Wavy and convex louver fin coils with different fin density, number of tube rows, and tube spacing and diameter have been investigated. A computer simulation program of air coils has been developed as a working tool in the experimental results treatment and manipulation. The obtained experimental results follow closely established trends of the literature regarding the effects of the geometric parameters over the thermo-hydraulic performance of the air flow in the coils. Some correlations from the literature compare reasonably well with the experimental results though some have shown important discrepancies. It has also been investigated the performance of the different geometric configurations through a second law of Thermodynamics analysis. Finally, experimental results have been curve fitted in such a way to develop generalized correlations for the air-side heat transfer and friction coefficients that include all the important geometric parameters of the aircoils. Such correlations have proved to fit the experimental results with reasonable accuracy.