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Proceedings of Symposium on Energy Engineering in the 21<sup>st</sup> Century (SEE2000) Volume I-IV

ISSN:
1-56700-132-7 (Print)

HEAT TRANSFER IN THE WAKE BEHIND A LONGITUDINAL VORTEX GENERATOR IMMERSED IN DRAG-REDUCING CHANNEL FLOWS

Jens F. Eschenbacher
Department of Mechanical Engineering, Kyoto University, Kyoto 606-8501, Japan

Mizuho Joko
Department of Mechanical Engineering Kyoto University

Kazuyoshi Nakabe
Department of Mechanical Engineering and Science, Kyoto University; Advanced Research Institute of Fluid Science and Engineering, Kyoto University, Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501, Japan

Kenjiro Suzuki
Department of Mechanical Engineering, Kyoto University, Kyoto; Department of Machinery and Control Systems, Shibaura Institute of Technology, 307 Fukasaku, Saitama, 337-8570, Japan

Abstract

An experimental study of wall heat transfer in the wake behind a single wing-type vortex generator (WVG) was made in drag-reducing flows with three different surfactant solutions, Cetyl-trimethyl-ammonium-chloride (CTAC) with same amounts of sodium salicylate (NaSal) dissolved in water. The additive concentration was varied between Oppm (CO), 30ppm (C30) and 200ppm (C200). The WVG was mounted on the heat transfer target surface of the bottom wall in the test section. The Reynolds number, based on the main flow velocity and the channel height was set in the range from 7.3 × 103 up to 4.4 × 104 under considerations of the temperature dependence of the non-Newtonian surfactant fluid. It was found, that small amounts of CTAC/NaSal added in water reduce the heat transfer coefficients drastically, and that this reduction could be locally recovered in the wake behind the WVG. The longitudinal vortex generated behind the WVG was found to play an important role for heat transfer enhancements of drag-reducing flows. Comparison with the case of pure water, CO, reveals that the heat transfer coefficients of the surfactant solutions can recover to the ones of Case CO locally in the wake behind the WVG. The heat transfer recovery regions correspond to the location of the longitudinal vortice which were observed narrower but longer in the surfactant solutions than in the pure water. Depending on the surfactant concentration, fluid temperature and flow velocity, the generated longitudinal vortex was locally able to recover the reduced wall heat transfer coefficient of the surfactant solution completely up to the value of water.