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Authors
Abstract(s)
Desde a revolução industrial, no século XIX, até aos dias de hoje, a temática da
dissipação de calor tem vindo a demonstrar um papel de elevada importância no
desempenho de qualquer tipo de máquina, evitando sobreaquecimentos danosos que
podem resultar numa ameaça à vida do ser humano. Assim, através do
desenvolvimento científico temos acesso às mais variadas formas de arrefecimento,
com recurso a meios gasosos ou líquidos em cooperação com superfícies
permutadoras, como é o caso das alhetas.
Nos primórdios da indústria aeronáutica foi crucial o arrefecimento dos motores a
pistons, principalmente devido ao desenvolvimento de maiores potências em
aeronaves militares e de competição. Com o avanço da tecnologia e com o
aparecimento dos motores de turbinas a gás, a preocupação constante de
arrefecimento tornou-se quase inexistente, passando a ser recorrente a aplicação de
permutadores de calor de superfície em elementos da aviónica do avião. Atualmente,
nos mais recentes motores, como por exemplo, o Turbo Fan de Ultra High Bypass,
com menores consumos, permitiram uma diminuição num dos principais absorsores
de calor, o combustível, voltando a existir uma aplicação de permutadores de calor
agora para arrefecimento do óleo.
Na presente dissertação desenvolve-se um trabalho experimental na ótica de
melhorar o desempenho térmico de uma superfície com alhetas. Para isso,
implementa-se o conceito de redireccionamento do escoamento para os canais das
alhetas, com recurso a superfícies defletores sobrepostas à superfície de alhetas. O
estudo faz uma comparação entre o desempenho de seis superfícies diferentes para a
situação com e sem defletores.
Os resultados demonstram um benefício geral para todas as superfícies ensaiadas.
Inclusive para gamas de velocidade diferentes. Verifica-se que para situações em que
o escoamento é substancialmente mais rápido também o efeito dos defletores é mais
notório.
Since the industrial revolution, in the 19th century, until nowadays, the subject of heat dissipation has demonstrated a highly important role in the performance of any type of machine, avoiding harmful overheating that can result in a threat to human life. Thus, through scientific development we have access to various forms of cooling, using gaseous or liquid media in cooperation with heat exchanger surfaces, as is the case of fins. In the early days of the aviation industry, it was crucial to cool the piston engines, mainly due to the development of higher power military and competition aircrafts. With the advance of technology and the appearance of gas turbine engines, the constant concern for cooling became almost non-existent, and the application of surface heat exchangers in the aircraft avionics elements became recurrent. Currently, in the most recent engines, as for example, the Turbo Fan Ultra High Bypass, with lower consumption, allowed a decrease in one of the main heat absorbers, the fuel, being again an application of heat exchangers now for oil cooling. In the present dissertation an experimental work is developed in order to improve the thermal performance of a finned surface. For that, the concept of redirecting the flow to the fin channels is implemented, using deflector surfaces superimposed on the finned surface. The study compares the performance of six different surfaces for the situation with and without deflectors. The results show an overall benefit for all surfaces tested. Even for different speed ranges. It is found that for situations where the flow is substantially faster the effect of the deflectors is also more noticeable.
Since the industrial revolution, in the 19th century, until nowadays, the subject of heat dissipation has demonstrated a highly important role in the performance of any type of machine, avoiding harmful overheating that can result in a threat to human life. Thus, through scientific development we have access to various forms of cooling, using gaseous or liquid media in cooperation with heat exchanger surfaces, as is the case of fins. In the early days of the aviation industry, it was crucial to cool the piston engines, mainly due to the development of higher power military and competition aircrafts. With the advance of technology and the appearance of gas turbine engines, the constant concern for cooling became almost non-existent, and the application of surface heat exchangers in the aircraft avionics elements became recurrent. Currently, in the most recent engines, as for example, the Turbo Fan Ultra High Bypass, with lower consumption, allowed a decrease in one of the main heat absorbers, the fuel, being again an application of heat exchangers now for oil cooling. In the present dissertation an experimental work is developed in order to improve the thermal performance of a finned surface. For that, the concept of redirecting the flow to the fin channels is implemented, using deflector surfaces superimposed on the finned surface. The study compares the performance of six different surfaces for the situation with and without deflectors. The results show an overall benefit for all surfaces tested. Even for different speed ranges. It is found that for situations where the flow is substantially faster the effect of the deflectors is also more noticeable.
Description
Keywords
Coeficiente Convectivo Convecção Forçada Fonte de Calor Superfícies Alhetadas