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Effects of combined rectangular ribs and delta winglets on forced convection heat transfer and friction loss behaviors for turbulent airflow through a constant heat flux heat exchanger channel are experimentally investigated in the present work. The ribs used to generate reverse/recirculation flow are placed on the one ribbed wall and two opposite walls plates of the tested channel while three pairs of delta winglets with 15 mm high (half height of channel, 0.5H), 60 mm long and two attack angles (α) of 60° and 45° were symmetrically placed on the lower plate at the entrance of the test channel to create longitudinal vortex flow at the entry. Three rib arrangements, namely, one ribbed wall, in-line and staggered ribs on two opposite walls were introduced. Measurements are carried out for the channel of aspect ratio, AR = 10 and height, H = 30 mm with a single rib height, e = 6 mm and rib pitch, P = 40 mm. The flow rate is in terms of Reynolds numbers based on the inlet hydraulic diameter of the channel in a range of 5000 to 22,000. The experimental results show that the use of winglets in conjunction with the ribs leads to the considerable increase in heat transfer coefficient and friction factor in comparison with the smooth channel. In common with the winglet, the in-line rib arrangement provides higher heat transfer and friction loss than the staggered one and the single rib but the staggered rib shows better thermal performance over others. The largest attack angle = 60 yields the highest increase in Nusselt number and friction factor while the = 45 provides the lowest. However, the highest thermal performance is found for using the = 45.
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Faculty of Engineering and Technology
Mahanakorn University of Technology
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