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Research Papers: Evaporation, Boiling, and Condensation

Effect of Temperature Difference on In-Tube Condensation Heat Transfer Coefficients

[+] Author and Article Information
Malcolm Macdonald

Sustainable Thermal Systems Laboratory,
GWW School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30382

Srinivas Garimella

Sustainable Thermal Systems Laboratory,
GWW School of Mechanical Engineering,
Georgia Institute of Technology,
Love Building, Room 340,
801 Ferst Drive,
Atlanta, GA 30382
e-mail: sgarimella@gatech.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received June 25, 2015; final manuscript received August 13, 2016; published online September 20, 2016. Assoc. Editor: Jim A. Liburdy.

J. Heat Transfer 139(1), 011502 (Sep 20, 2016) (9 pages) Paper No: HT-15-1435; doi: 10.1115/1.4034495 History: Received June 25, 2015; Revised August 13, 2016

The effect of temperature difference (Tsat − Tcoolant) on condensation heat transfer coefficients inside horizontal tubes is investigated in detail. Condensation experiments are conducted on propane inside a 7.75 mm horizontal tube at four temperature differences between the test fluid and coolant at three mass fluxes and four saturation temperatures. The heat transfer coefficient is shown to increase with temperature difference, with this effect diminishing with larger temperature differences, and being most significant at higher saturation temperatures. Heat transfer coefficients at the low-reduced pressures (Pr = 0.25) corresponding to lower saturation temperatures (30 °C) are mostly unaffected by the temperature difference. Subcooling of the condensate is expected to increase heat transfer coefficients at the larger temperature differences. Flow visualization studies are used to explain the inadequacy of the Nusselt film theory for the conditions investigated. The underlying mechanisms are also used to explain why the correlations from the literature do not predict the observed trend, and a new correlation to account for the effect of temperature difference is developed.

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References

Figures

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Fig. 1

Measured heat transfer coefficients for all of the test conditions

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Fig. 2

Slope of heat transfer coefficients with increasing test-to-coolant temperature difference

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Fig. 3

Developing temperature profiles and subcooled and phase-change regions

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Fig. 4

Thermal conductivity changes with temperature

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Fig. 5

Nusselt number based on liquid thermal conductivity at wall temperature

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Fig. 6

Flow visualization of the two-phase flow inside 7 and 15 mm diameter tubes

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Fig. 7

Cavallini et al. correlation compared to the measured heat transfer coefficients

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Fig. 8

Comparison of the proposed correlation and the observed trends

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Fig. 9

Demonstration of improved predictions possible using the subcooling correlation with two correlations from the literature

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