Experimental investigation of heat transfer and friction factor characteristics of solar air heater using wavy delta winglets

•Wavy winglets offer superior thermal performance over smooth channel.•Heat transfer rate increases with decreasing relative longitudinal pitch.•Wavy winglet offer best TEF performance of order of 2.09 at ϕ=5, P/H=3. In the present work experimental investigation on the heat transfer and friction characteristics of a solar air heater duct roughened with wavy-up delta winglet vortex generators placed on absorber plate having a uniform wall heat flux is carried out. Reynolds number in the present study is taken in the range 4000–17,300 based on the hydraulic diameter of the channel. The investigated parameters of wavy delta winglets are no of waves (ϕ): 3, 5, 7 and relative longitudinal pitch (P/H): 3, 4, 5 and 6, respectively at single angle of attack (α): 60°. The comparison of the staggered and inline arrangement reveals that the inline arrangement produces the higher Nusselt Number. The maximum Nusselt number enhancement was found to be 223% over the flat plate using a relative longitudinal pitch of 3 with five wave winglets at Reynolds number of 4000 with an increase in friction factor by 10.3 times. The thermohydraulic performance obtained for the configuration was 2.09.