Turbulent Heat Transfer Enhancement in

a Heat Exchanger Using Rib and Delta Winglet

Sompol Skullong

Department of Mechanical Engineering, Faculty of Engineering at Si Racha

Kasetsart University Si Racha Campus, 199 M.6, Sukhumvit Rd.

Tungsukla, Si Racha, Chonburi 20230, Thailand

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and Pongjet Promvonge

Department of Mechanical Engineering, Faculty of Engineering

King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, Thailand

Manuscript received February 25, 2014

Revised March 24, 2014

ABSTRACT

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 attackangles (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 ribbut the staggered rib shows better thermal performance over others.The largest attack angle a = 60° yields the highest increase in Nusselt number and friction factor while the a = 45° provides the lowest. However, the highest thermal performance is found for using the a = 45°.

 

Keywords: turbulent channel flow, rectangular rib, winglet, thermal performance,friction loss

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