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International Symposium on Imaging in Transport Processes.
May, 25-29, 1992, Athens, Greece

DOI: 10.1615/ICHMT.1992.IntSympImgTranspProc


ISBN Print: 978-1-56700-012-2

COMPUTER-AIDED VISUALIZATION OF THE LOCAL VOID FRACTION DISTRIBUTION IN A GAS-SOUD FLUIDIZED BED

pages 87-96
DOI: 10.1615/ICHMT.1992.IntSympImgTranspProc.100
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Краткое описание

Gas-solid fluidized beds have been applied to many kinds of heat transfer equipments, such as chemical reactors and solid fuel combustors as well as heat exchangers, because of their excellent heat transfer characteristics. It is believed that the high heat transfer coefficients of gas-solid fluidized beds are basically attributed to thermal and hydrodynamic interactions between fluidized particles and surrounding gas flow/solid surfaces. A number of researchers studied the mechanisms of heat transfer enhancement of the gas-solid fluidized beds, and many correlations and heat transfer models have been reported in the literature.
The authors have studied the microscopic mechanisms of heat transfer enhancement of a fluidized bed [1]. In that study, solid contact between fluidized particles and heat transfer surface was visualized, and the contact duration and frequency were measured so as to estimate the heat transfer enhancement due to direct-contact heat exchange between the fluidized particles and the heat transfer surface immersed in the bed. The obtained results clearly show that the heat exchange through direct contact between particles and heat transfer tube plays an important role in enhancing heat transfer of the bed at the incipient fluidization, but that the importance rapidly decreases with the increase in fluidizing gas flow rate, because number density of the particles around the tube decreases with it. In this sense, number density distribution of particles, i.e. void fraction distribution, has a serious influence upon the heat transfer characteristics of gas-solid fluidized beds.

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