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Research Papers: Heat Exchangers

Visualization of Two-Phase Flow in Serpentine Heat Exchanger Passages With Microscale Pin Fins

[+] Author and Article Information
Dhruv C. Hoysall

G.W. Woodruff School of
Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332
e-mail: dhoysall3@gatech.edu

Khoudor Keniar

G.W. Woodruff School of
Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332
e-mail: kkeniar3@gatech.edu

Srinivas Garimella

Fellow ASME
G.W. Woodruff School of
Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332
e-mail: sgarimella@gatech.edu

1Corresponding author.

Presented at the 5th ASME 2016 Micro/Nanoscale Heat & Mass Transfer International Conference. Paper No. MNHMT2016-6576. Zhang.Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received May 31, 2016; final manuscript received March 23, 2017; published online August 23, 2017. Assoc. Editor: Zhuomin

J. Heat Transfer 140(1), 011802 (Aug 23, 2017) (9 pages) Paper No: HT-16-1340; doi: 10.1115/1.4037342 History: Received May 31, 2016; Revised March 23, 2017

Microchannel heat exchangers offer the potential for high heat transfer coefficients; however, implementation challenges must be addressed to realize this potential. Maldistribution of phases among the microchannels and the changing phase velocities associated with phase change present design challenges. Flow maldistribution and oscillatory instabilities can affect transfer rates and pressure drops. In condensers, evaporators, absorbers, and desorbers, changing phase velocities can change prevailing flow regimes from favorable to unfavorable. Geometries with serpentine passages containing pin fins can be configured to maintain favorable flow regimes throughout the component for phase-change heat and mass transfer applications. Due to the possibility of continuous redistribution of the flow across the pin fins along the flow direction, maldistribution can also be reduced. These features enable high heat transfer coefficients, thereby achieving considerable compactness. The characteristics of two-phase flow through a serpentine passage with micro-pin fin arrays with diameter 350 μm and height 406 μm are investigated. An air–water mixture is used to represent two-phase flow through the serpentine test section, and flow features are investigated using high-speed photography. Improved flow distribution is observed in the serpentine geometry. Distinct flow regimes, different from those observed in microchannels, are also established. Void fraction and interfacial area along the length of the serpentine passages are compared with the corresponding values for microchannels. A model developed for the two-phase frictional pressure drops across this serpentine micro-pin fin geometry predicts experimental values with a mean absolute error (MAE) of 7.16%.

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References

Figures

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Fig. 1

Schematic of experimental setup

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Fig. 2

Illustration of test section geometry

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Fig. 3

Illustration of the test section assembly

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Fig. 4

Representative image of flow through test section

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Fig. 5

Data reduction algorithm for the analysis of flow videos

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Fig. 6

Processed image showing interfaces and flow area

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Fig. 7

Void fraction variation with window

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Fig. 8

Comparison of different void fraction models with measured data

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Fig. 9

Flow distribution through serpentine section

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Fig. 10

Flow distribution along the length of the test section

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Fig. 11

Comparison of interfacial area intensity between microchannels and serpentine micro-pin fin geometry

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Fig. 12

Interfacial area distribution through serpentine section

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Fig. 13

Comparison of pressure drop contributions

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Fig. 14

Comparison of pressure drop data with the literature

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Fig. 15

Comparison of pressure drop data with model predictions

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