| 摘 要： | The paper presents an experimental study on the heat transfer and flow friction characteristics in a solar air heater channel fitted with delta-winglet type vortex generators(DWs).The experiments are conducted by varying the airflow rate for Reynolds number in the range of 5000 to 24000 in the test section with a uniform heat-flux applied on the upper channel wall.Firstly,the DW pairs are mounted only at the entrance of the lower wall of the test channel(called DW-E)to create multiple vortex flows at the entry.The effect of two transverse pitches(RP Pt/H 1 and 2)at three attack angles(α30°,45°and 60°)of the DW-E with its relative height,b/H 0.5(half height of channel)is examined.Secondly,the 30°DWs with three different relative heights(b/H 0.3,0.4 and0.5)are placed on the upper wall only(absorber plate,called DW-A)of the test channel.The experimental result reveals that in the first case,the 60°DW-E at RP1 provides the highest heat transfer and friction factor while the30°DW-E at RP1 performs overall better than the others.In the second case,the 30°DW-A at b/H 0.5 yields the highest heat transfer and friction factor but the best thermal performance is found at b/H 0.4.
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