This study presents visual observation and frictional performance of the wavy channels. A total of three test sections including two wavy channels with corrugation angle of 15 and 30 degrees and a plain channel were examined in this study. The observed range is from Re = 300 to Re = 2100. A detectable flow re-circulation is seen at the leeside of the wavy channel for θ = 30° and Re = 300. This phenomenon is seen even in the first corrugation of the 30° wavy channel but is not seen for 15° corrugation channel. As the Reynolds number is increased to 500, the flow field for θ = 30° is quite unsteady and shedding transverse vortices are seen at the leeward portion of the corrugation channel. A very special phenomenon of the split and turn around of the dye streak located at the leeward of the second corrugation is observed. This phenomenon is also seen at the corrugation angle of θ = 15° and Re = 1000. The pressure drops of the wavy channels increase significantly with the corrugation angles. The pronounced increase of the pressure drop of the wavy channel is directly linked to the presence of flow-recirculation and the strong turbulent mixing caused by the corrugation.
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