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|Título:||Granular beds composed of different particle sizes: experimental and CFD approaches|
|Autor:||Dias, Ricardo P.|
Fernandes, Carla S.
Computational fluid dynamics
|Citação:||Dias, Ricardo P.; Fernandes, Carla S. (2009) - Granular beds composed of different particle sizes: experimental and CFD approaches. In Porous Media: Heat and Mass Transfer, Transport and Mechanics. p. 151-170. ISBN 978-1-60741-401-8|
|Resumo:||The porosity, tortuosity, permeability and heat exchange characteristics from binary packings, containing mixtures of small d and large D spherical particles, are analysed in the present work. Binary packing porosity (ε), tortuosity (τ), permeability and heat exchange performance are dependent on the volume fraction of large particles, xD, present in the mixtures, as well as on the particle size ratio, δ = d/D. In the region of minimum porosity from the binary mixtures (containing spheres with diameter d and D), heat exchange performance and permeability from binary packing are higher than that of the packing containing the small particles d alone (mono-size packing). The δ region where the permeability of binary packing is higher than the permeability of mono-size packing of particles d is located in the range 0.1 ≤ δ < 1.0. An increase in permeability by a factor of two is achieved for particle size ratios between 0.3 and 0.5. Tortuosity can be modelled by the simple function τ = 1/ε α and it is shown that, in the region of minimum porosity, α varies between 0.5 (mono-size packing) and 0.4 (binary packing with δ close to 0.03). Due to the tortuosity increase, binary mixtures give rise to Kozeny´s coefficients substantially higher than five. Using the commercial finite element software package POLYFLOW® it was possible to confirm the heat exchange enhancement referred above. The obtained improvement on the thermal performance is related to the increase of effective thermal conductivity in the binary packing and to the increase in transversal thermal conductivity due to the porosity decrease and tortuosity increase. For non-Newtonian fluids from the power-law type, τ decreases with the decrease of the flow index behaviour|
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