DETERMINAÇÃO EXPERIMENTAL DOS COEFICIENTES DE TRANSPORTE DA PASTA DE GELO EM TROCADORES DE CALOR DE PLACAS / EXPERIMENTAL DETERMINATION OF TRANSPORTATIONS COEFFICIENTS FOR ICE SLURRY IN PLATE HEAT EXCHANGERS

AUTOR(ES)

LUIS CARLOS CASTILLO MARTINEZ

DATA DE PUBLICAÇÃO

2005

RESUMO

Ice slurry is an aqueous solution from which ice crystals are formed. These crystals possess high energy density, in the form of latent heat. Furthermore, the fact of being a slurry makes it an excellent energy carrier, for it can be easily pumped. The present work presents an experimental procedure to assess the heat transfer and the pressure loss, with phase change, using a mixture of propyleneglycol and water, 13.8% weight, in a U-plate heat exchanger with 16 plates. Tests were carried out for both parallel and counter-flow configurations of the heat exchanger, for two different mass fractions of ice and with Reynolds numbers between 150 and 425 for the slurry. Different thermal loads were considered. The experiments showed increases of up to 25% in the overall heat transfer coefficient when the slurry flow is increased, with consequent increase in the Reynolds number. By increasing the ice fraction the cooling capacity is improved, reducing the Nusselt number. In the literature, this relationship is not clearly defined, as some authors show gains in the heat exchange coefficient, losses, and some others did not observe any influence on this parameter. Regarding the heat exchange configuration, i.e., parallel or counter-flow, neither the heat exchange coefficient, nor the Nusselt number suffered major influence. The effectiveness is up to 10% higher for the counter-flow configuration in comparison with the parallel configuration. The figures found for the friction coefficient, between 0,030 and 0,085, are in good agreement with the literature. As expected, the friction coefficient decreases when the mass flow is increased, and increases when the ice fraction is increased.

ASSUNTO(S)

mudanca de fase refrigerante secundario pasta de gelo ice slurry perda de carga coeficiente de troca de calor trocador de calor de placas heat exchange coefficient secondary refrigerant phase change plate heat exchanger pressure loss

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