International Journal of Mechanical Engineering and Robotics Research Vol. 9, No. 1, January 2020 © 2020 Int. J. Mech. Eng. Rob. Res 130 doi: 10.18178/ijmerr.9.1.130-135 Performance Evaluation of Solar Receiver Heat Exchanger with Rectangular-Wing Vortex Generators Narin Koolnapadol Department of Automotive Mechanical Engineering, Faculty of Industrial Technology, Rajabhat Rajanagarindra University, Chachoengsao 24000, Thailand Pongjet Promvonge Department of Mechanical Engineering, Faculty of Engineering, King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, Thailand Sompol Skullong* Department of Mechanical Engineering, Faculty of Engineering at Sriracha, Kasetsart University Sriracha Campus, 199 M.6, Sukhumvit Rd., Sriracha, Chonburi 20230, Thailand E-mail: sfengsps@src.ku.ac.th, sompol@eng.src.ku.ac.th Abstract—The paper presents an experimental investigation on heat transfer and flow resistance in a solar air heater (SAH) duct with rectangular-wing vortex generators (RWVGs) on the absorber plate to increase the SAH system performance. The experimental work is carried out in the test duct with its aspect ratio (AR) of 10 for Reynolds number (Re) based on the hydraulic duct diameter ranging from 5290 to 22,700. The RWVGs are placed on the absorber with three attack angles (  ° ° and 60°) and three relative wing pitches (P R = P l /H = 1.0, 1.5 and 2.0) at a single relative wing height (B R =b/H=0.67). The experimental result shows that the use of RWVGs leads to the considerable increase in Nusselt number (Nu) over the flat- plate duct (smooth duct) around 4.06–5.79 times while the increase in friction factor (f) is about 11.43–43.97 times. The Nu and f display the increasing trend with the rise of  but show the opposite trend for the increment of P R . The highest thermal performance for using the RWVG roughness is some 1.95 at   ° and P R = 1.5. Correlations for Nu and f have also been developed and determined as a function of RWVG parameters. Index Terms—solar air heater, vortex generators, flow resistance, thermal performance I. INTRODUCTION To achieve renewable and clean energy, several solar energy/power technologies are under development and some can produce electric power by converting sunlight into thermal energy at high temperature of gas/steam to obtain the turbine work for electrical generator. However, the efficiency or performance of the current solar plants/solar thermal systems is not high. It has been suggested that the potential way to increase the thermal performance of solar thermal systems is to introduce a Manuscript received July 28, 2018; revised August 15, 2019. vortex generator (VG) device. VG devices in the form of ribs [1,2], fins [3], baffles [4], winglets [5,6] and wings [7] are passive elements widely used to enhance the rate of heat transfer in various thermal systems. VG devices provide excess heat transfer area to fluid streams which results in the rate of heat transfer. Earlier investigations have been conducted to study the effect of VG devices on heat transfer enhancement in the heat exchanger/solar air heater systems [8-11]. The effect of rib size and arrangement on turbulent heat transfer and flow friction characteristics in a solar air heater channel was experimentally investigated by Skullong et al. [12], while the thermal and flow resistance in a square duct fitted diagonally with angle-finned tapes were studied experimentally and numerically by Promvonge et al. [13,14]. Tamna et al. [15] examined thermal performance enhancement in a solar air heater (SAH) channel with multiple V-baffle vortex generators (BVG) and concluded that the single BVG with PR = 0.5 yields the highest thermal performance. Skullong et al. [16] also investigated thermal behaviors in a SAH channel using wavy grooves incorporated with pairs of trapezoidal- winglets (TW) placed on the absorber plate and found that the highest thermal performance was obtained for the wavy-groove in common with the TW at P R = 1 and B R = 0.24. The effect of delta-wing vortex generators located at the leading edge of a flat plate on heat transfer behaviors was reported by Gentry and Jacobi [17]. Following the above literature review, the utilization of winglets/wings has been found to give more attractive than other VG devices due to lower pressure loss. In general, winglets/wings are designed to create longitudinal vortices that can help increase turbulence levels leading to improvement of the rate of heat transfer, albeit with a minimal pressure loss penalty. However, the winglets/wings cited above, in general, have been widely used to improve the thermal performance of fin-tube heat