Experimental studies of the secondary flow structure and its enhancement on the heat transfer in a horizontal divergent channel have been carried out. The bottom wall is horizontal and is heated uniformly, and while the opposite wall is insulated and inclined with respect tot he horizontal plane so as to create a divergence angle of 3 deg . The aspect ratio (width to height) and the ratio of channel length to height at the entrance of the channel is 6.67 and 15. The Reynolds number ranges from 100 to 2000 and the buoyancy parameter, Gr/Re~2, from 0 to 405. Flow structure inside the channel is visualized by injecting smoke at the inlet flowing along the bottom wall. Secondary flow appearing as mushroom-shaped plumes associated with vortices is also found in the divergent channel. The adverse pressure gradient in the diveragent channel causes a thicker heated layerin the bottom and earlier initiation of secondary flow. The mteraction between neighboring vortices and plumes becomes highly unstable. This causes an earlier and larger enhancement of the heat transfer than the case of the parallel-plate channel. The highly unstable interaction between neighboring plumes in the downstream precludes the formation of steady two-dimensional longitudinal vortex rolls. Temperature fluctuations at different locations are measured to indicate the flow structure and oscillation of the secondary flow. The effects of the buoyancy parameter and the divergence of the channel on the secondary flow structure and the Nusselt number are presented and ddiscussed.
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