| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系 === 85 === Experiments were performed to study the heat transfer behavior
of secondaryflow in horizontal convergent or divergent channel
heated from below for airflow. The experiment is devised for two
parts. The first one is wall heat transfer distribution
measurement, the other is flow visualization.Both of them can
provide an understanding to the physical phenomenon.One of the
side walls which maintains horizontal is heated uniformly and
the opposite wall which has a convergent or divergent angle of 3
is insulated. During the experiment, the Reynolds number of the
main forced flow ranges from 105 to 1000 and the buoyancy
parameter varies from 1.5 to 907.In horizontal channel, the
buoyancy induced secondary flow can produce plume and mushroom-
like vortices which can significantly increase the heattransfer
in the channel. In the divergent channel, the adverse pressure
gradient causes a thicker bottom heated layer as well as a much
earlier initiation of plumes and earlier interaction between
neighboring vortices and plumes which become unsteady in the
downstream. In convergent channel,the favorable pressure
gradient causes a thinner bottom heated layer and amuch later
initiation of secondary flow. The effect of buoyancy is
reducedin the downstream regime where the flow acceleration is
significant.
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