Experimental Investigation on Turbulent Convection in Solar Air Heater Channel Fitted with Delta Winglet Vortex Generator

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 (R-P = P-t/H = 1 and 2) at three attack angles (alpha = 30 degrees, 45 degrees and 60 degrees) of the DW-E with its relative height, b/H = 0.5 (half height of channel) is examined. Secondly, the 30 degrees DWs with three different relative heights (b/H = 0.3, 0.4 and 0.5) 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 degrees DW-E at R-P = 1 provides the highest heat transfer and friction factor while the 30 degrees DW-E at R-P = 1 performs overall better than the others. In the second case, the 30 degrees 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.