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Research Papers: Heat Transfer Enhancement

Experimental and Numerical Study of Heat Transfer and Flow Friction in Channels With Dimples of Different Shapes

[+] Author and Article Information
Yu Rao

Gas Turbine Research Institute,
School of Mechanical Engineering,
Shanghai Jiao Tong University,
Dongchuan Road 800,
Shanghai 200240, China
e-mail: yurao@sjtu.edu.cn

Yan Feng, Bo Li

Gas Turbine Research Institute,
School of Mechanical Engineering,
Shanghai Jiao Tong University,
Dongchuan Road 800,
Shanghai 200240, China

Bernhard Weigand

Institute of Aerospace Thermodynamics (ITLR),
University of Stuttgart,
Pfaffenwaldring 31,
Stuttgart 70569, Germany

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received May 29, 2014; final manuscript received November 6, 2014; published online December 2, 2014. Assoc. Editor: Danesh / D. K. Tafti.

J. Heat Transfer 137(3), 031901 (Mar 01, 2015) (10 pages) Paper No: HT-14-1353; doi: 10.1115/1.4029036 History: Received May 29, 2014; Revised November 06, 2014; Online December 02, 2014

An experimental and numerical study was conducted to investigate the effects of dimple shapes on the heat transfer and flow friction of a turbulent flow over dimpled surfaces with different dimple shapes: spherical, teardrop, elliptical, and inclined elliptical. These dimples all have the same depth. The heat transfer, friction factor, and flow structure characteristics in the cooling channels with dimples of different shapes have been obtained and compared with each other for a Reynolds number range of 8500–60,000. The study showed that the dimple shape can have distinctive effects on the heat transfer and flow structure in the dimpled channels. The teardrop dimples show the highest heat transfer, which is about 18% higher than the conventional spherical dimples; and the elliptical dimples have the lowest heat transfer, which is about 10% lower than the spherical dimples; and however the inclined elliptical dimples have comparable heat transfer and pressure loss performance with the spherical dimples. The experiments still showed the realistic heat transfer enhancement capabilities of the dimpled channels relative to a smooth rectangular channel flow under the same flow and thermal boundary conditions, even after considering the thermal entrance effects in the channel flow and the enlarged heat transfer (wetted) area due to the dimpled surface. The three-dimensional numerical computations showed different vortex flow structures and detailed heat transfer characteristics of the dimples with different shapes, which revealed the influential mechanisms of differently shaped dimples on the convective heat transfer enhancement.

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Figures

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Fig. 1

Dimple array geometrical parameters

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Fig. 2

Geometrical parameters of the dimples with different shapes

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Fig. 3

Schematic of the experimental system for the dimpled channels

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Fig. 4

Schematic of the boundary conditions for the dimpled channel computation

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Fig. 5

The mesh for the spherical dimple channel computation

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Fig. 6

Averaged Nusselt numbers of the dimpled channels

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Fig. 7

Heat transfer enhancement of the dimpled channels

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Fig. 8

Realistic heat transfer enhancement of the dimpled channels

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Fig. 9

Local Nusselt numbers on the dimpled surfaces with various dimple shapes at Re = 50,500

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Fig. 10

Friction factors of the dimpled channels

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Fig. 11

Friction factor ratios of the dimpled channels

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Fig. 12

Three-dimensional streamlines in the dimpled channels with various dimple shapes at Re = 50,500. The legend for the Nusselt numbers is the same with Fig. 9.

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Fig. 13

Streamlines and TKE distribution in a plane with a distance of 0.25 mm away from the endwall in the dimpled channels for Re = 50,500

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Fig. 14

Comparisons of overall thermal performance of the dimpled channels

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