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A V-shaped trapezoidal-rib placed on the absorber plate of a channel solar air heater is a newly design with the benefit combination between the inclined-surface of rib sides to reduce the friction factor and V-shaped ribs to create counter-rotating vortices for increasing the heat transfer rate is presented using the 3D numerical method. The rib height ratio, HR=0.04, 0.06, 0.08 and 0.10, pitch ratio, PR=0.4, 0.6, 0.8 and 1.0, base-rib wide ratio, WR=0.10, 0.15 and 0.20 at a constant attack angle, α=30o and rib-tip wide ratio, t/H=0.05 are parameters of interest in investigating in the turbulent region with Reynolds number, Re=3000-20,000. The numerical results revealed that the V-shaped trapezoidal-rib absorber gives the fully developed periodic flow and heat transfer at x/H=10. The V-shaped trapezoidal-rib absorber generates the counter-rotating-vortices in the form of common-flow-down vortices leading to the induction of impinging flow on the absorber surface apart from disrupting the thermal boundary layer and increasing the fast fluid mixing. These phenomena result in the greater increase of the heat transfer rate. The rise of HR and the decrease of PR and WR provide the increment of friction factor while the increase of the heat transfer depends on HR, PR and WR values. In the range investigated, the Nu/Nu0, f/f0 and TEF are in the range of 1.16-4.57, 1.78-10.44 and 0.84-2.53, respectively. At HR=0.08, PR=0.6 and WR=0.20 the highest TEF and Nu/Nu0 are found to be around 2.53 and 4.57 at Re=3000, respectively.
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Faculty of Engineering and Technology
Mahanakorn University of Technology
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