Research Papers

Thermo-economic Limitations of Ambient Heat Rejection in Vertical Fin Arrays With Buoyancy-Driven Flow Enhancement Through the Chimney Effect

[+] Author and Article Information
Noris Gallandat

George W. Woodruff School
of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332

J. Rhett Mayor

Associate Professor
George W. Woodruff School
of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332
e-mail: rhett.mayor@me.gatech.edu

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received August 28, 2015; final manuscript received July 9, 2016; published online September 8, 2016. Editor: S.A. Sherif.

J. Thermal Sci. Eng. Appl 9(1), 011001 (Sep 08, 2016) (8 pages) Paper No: TSEA-15-1247; doi: 10.1115/1.4034338 History: Received August 28, 2015; Revised July 09, 2016

This paper presents the thermo-economic limits of ambient heat rejection in vertical fin arrays with buoyancy-driven flow enhancement through the chimney effect. A one-dimensional semi-analytical thermo-fluidic model is developed to assess the cooling power enhancement of the proposed heat sink design. A bi-objective optimization is performed utilizing genetic algorithm to present the tradeoffs between the cost and the thermal performance of a heat sink. For the considered baseplate geometry, the maximal cooling power without a chimney amounts 1540 W at a heat flux of 1.03 W/cm2. By adding a chimney up to 2.5 m high, the cooling power is increased by 46% to 2250 W at a heat flux of 1.50 W/cm2.

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Fig. 1

Heat Sink design and dimensions for the case without chimney (left) and with chimney (right)

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Fig. 2

Geometric parameters of the fin array (left) and equivalent thermal resistance network (right)

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Fig. 3

Absorbed radiative power, emitted radiation, and net radiative heat exchange between the heat sink and the surroundings

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Fig. 4

Parametric study on the overall thermal resistance on the channel width in the case with natural convection only for the channel width s (a), the fin length d (b), and the fin thickness t (c)

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Fig. 5

Air velocity and Reynolds number in the cooling channel as a function of the chimney height

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Fig. 6

Pressure drop and buoyancy gains as a function of the chimney height

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Fig. 7

Thermal resistance of the system as a function of the chimney height

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Fig. 8

Parametric study on the overall thermal resistance on the channel width in the case with chimney for the channel width s (a), the fin length d (b), and the fin thickness t (c). Notice that the optimal channel width is smaller as compared to the case without a chimney.

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Fig. 9

Comparison of the design tool with the results obtained from an FEA simulation

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Fig. 10

Flow chart describing the optimization process

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Fig. 11

Pareto front for the heat sink with natural convection only

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Fig. 12

Pareto front for the heat sink with enhanced flow through the chimney effect



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