Estudo teórico-experimental da transferência de calor e do fluxo crítico durante a ebulição convectiva no interior de microcanais
Data
2017-11-15
Autores
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Biblioteca Digital de Teses e Dissertações da USP
Universidade de São Paulo
Escola de Engenharia de São Carlos
Universidade de São Paulo
Escola de Engenharia de São Carlos
Resumo
Descrição
A pesquisa realizada tratou do estudo da transferência de calor e do fluxo crítico durante a ebulição convectiva no interior de canais de diâmetro reduzidos a partir de dados levantados em bancadas experimentais construídas para esta finalidade. Extensa pesquisa bibliográfica foi efetuada e os principais métodos disponíveis para previsão de coeficiente de transferência de calor, fluxo crítico e mapas de escoamento foram levantados. Os resultados obtidos foram parametricamente analisados e comparados com os métodos da literatura. Pela primeira vez para microcanais, resultados experimentais foram levantados por um mesmo autor em laboratórios distintos buscando verificar a tendência e comportamentos. Tal comparação tem sua importância destacada em face das elevadas discrepâncias observadas na literatura quando resultados de autores distintos, obtidos em condições similares, são comparados. Os resultados levantados foram utilizados na elaboração de modelos que consideram os padrões de escoamento observados em microcanais. A incorporação dos padrões permitiu o desenvolvimento de modelos mecanísticos para coeficiente de transferência de calor, fluxo crítico e critérios para a caracterização da transição entre macro e microcanais baseados na formação do padrão de escoamento estratificado e na simetria do filme líquido no escoamento anular.
This research comprises an experimental and theoretical study on flow boiling heat transfer and critical heat flux inside small diameter tubes based on data obtained in experimental facilities specially designed for this purpose. A broad literature review was carried out and the main methods to predict the heat transfer coefficient, critical heat flux and flow patterns were pointed out. The experimental results were parametrically analyzed and compared against the predictive methods from literature. For the first time, microchannels experimental results obtained by an unique researcher in distinct laboratories were compared and a reasonable agreement was observed. The importance of such a comparison is high-lighted for flow boiling inside microchannels due to the high discrepancies ob-served when results from independent laboratories obtained under similar experimental conditions are compared. Moreover, the experimental results obtained in the present study were used to develop correlations and models for the heat transfer coefficient and heat flux that takes into account the flow patterns observed in microchannels. The heat transfer coefficient and critical heat flux models were developed based on mechanistic approach. In addition, criteria to characterize macro to microchannel transition were proposed based in the occurrence of the stratified flow pattern and the liquid film symmetry under annular flow conditions.
This research comprises an experimental and theoretical study on flow boiling heat transfer and critical heat flux inside small diameter tubes based on data obtained in experimental facilities specially designed for this purpose. A broad literature review was carried out and the main methods to predict the heat transfer coefficient, critical heat flux and flow patterns were pointed out. The experimental results were parametrically analyzed and compared against the predictive methods from literature. For the first time, microchannels experimental results obtained by an unique researcher in distinct laboratories were compared and a reasonable agreement was observed. The importance of such a comparison is high-lighted for flow boiling inside microchannels due to the high discrepancies ob-served when results from independent laboratories obtained under similar experimental conditions are compared. Moreover, the experimental results obtained in the present study were used to develop correlations and models for the heat transfer coefficient and heat flux that takes into account the flow patterns observed in microchannels. The heat transfer coefficient and critical heat flux models were developed based on mechanistic approach. In addition, criteria to characterize macro to microchannel transition were proposed based in the occurrence of the stratified flow pattern and the liquid film symmetry under annular flow conditions.
Palavras-chave
Coeficiente de transferência de calor, Microcanais, Fluxo crítico de calor, Ebulição convectiva, Padrão de escoamento, Flow boiling, Flow pattern, Heat transfer coefficient, Critical heat flux, Microchannel