^bDepartment of Mechanical Engineering, Faculty of Engineering, King Mongkut’s Institute of Technology Ladkrabang, Bangkok, Thailand

^cDepartment of Mechanical Engineering, Faculty of Engineering at Sriracha, Kasetsart University Sriracha Campus, 199 M.6, Sukhumvit Rd., Sriracha, Chonburi, Thailand

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Abstract:An experimental study has been conducted to investigate heat transfer, friction loss and thermal performance characteristics of turbulent flow in a solar air heater channel artificially roughened on one side (absorber plate) with multiple perforated-winglet vortex generator (PWVG). Air as the working fluid enters the test duct having a uniform surface heat-flux with Reynolds number (Re) ranging from 5200 to 24,000 in the present work. Effects of four  different punched hole/pore diameters of winglet (d=2 mm, 4 mm, 6 mm and 8 mm) at a single relative winglet height (R_B=b/H=0.6), relative winglet pitch (R_P=P/H=3) and attack angle (β = 60°) on thermal characteristics are examined. The experimental results show that the PWVG provides the drastic increase in Nusselt number (Nu) and friction factor (f) values over the flat/smooth channel. In addition, substantial increases in Nu and f values are found for the rise in hole sizes. The maximum Thermal Enhancement Factor (TEF) is found for the pore diameter of 2 mm at lower Reynolds number. The present results are also compared with the results from the typical or solid winglet, TWVG (non-punched hole of winglet).

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