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Главная Архив Thermal Letter Оргкомитет Будущие конференции AIHTC
International Heat Transfer Conference 12

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

Heat transfer enhancement by an immiscible droplet wobbling in near-wall region of turbulent flow

Yoshimichi Hagiwara
Department of Mechanical and System Engineering, Graduate School of Science and Technology, Kyoto Institute of Technology Goshokaido-cho, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan

Takuji Yuge
Department of Mechanical and System Engineering, Kyoto Institute of Technology, Goshokaido-cho, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan

Toshihiko Iwasaki
Department of Mechanical and System Engineering, Kyoto Institute of Technology Goshokaido-cho, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan

DOI: 10.1615/IHTC12.500
6 pages

Аннотация

The direct numerical simulation has been carried out for turbulent downward flow in a vertical channel with an immiscible droplet whose density is lower than that of the flowing fluid. The modified Volume-of-Fluid (VOF) method has been used for tracking the interface. To reduce the numerical diffusion further in this method, a local grid refinement, for which the mass conservation is satisfied for the fine grid system, has been applied in the domain surrounding the droplet. The energy equation is solved under the condition of uniform wall temperature. The physical properties for the governing equations are well approximated near the liquid-liquid interface using the fine grids. It is found fromthe computational result that low-temperature fluid is pushed into the buffer region by the wallward flow along the cap of the droplet. Also, the outward flow induced by the droplet wake flow causes the liftup of the hot fluid adjacent to the wall. These flows enhance the near-wall heat transfer.
We have also conducted the measurement for turbulent water downward flow in a duct with rising Dodecane droplets. The water flow was visualized by tracer particles. Aparticle tracking velocimetry (PTV) and a particle image velocimetry (PIV) have been applied for the visualized images. It is observed in the experiment that the droplet rises with wobbling near the duct wall. This droplet motion is due to the lift force and the asymmetric evolution of vortex in the droplet wake flow. This wake flow modifies the near-wall turbulence: the lift-up of low-speed fluid is not observed clearly near the droplet. The deformation of the droplet is found when the direction of the droplet is changed from wallward to outward in its wobbling.

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