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Research Papers: Evaporation, Boiling, and Condensation

Effects of Pressure and a Microporous Coating on HFC-245fa Pool Boiling Heat Transfer

[+] Author and Article Information
Gilberto Moreno

National Renewable Energy Laboratory,
Golden, CO 80401
e-mail: gilbert.moreno@nrel.gov

Jana R. Jeffers, Sreekant Narumanchi

National Renewable Energy Laboratory,
Golden, CO 80401

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received September 27, 2013; final manuscript received June 27, 2014; published online July 22, 2014. Assoc. Editor: W. Q. Tao. The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes.

J. Heat Transfer 136(10), 101502 (Jul 22, 2014) (9 pages) Paper No: HT-13-1510; doi: 10.1115/1.4027966 History: Received September 27, 2013; Revised June 27, 2014

A study was conducted to experimentally characterize the pool boiling performance of hydrofluorocarbon HFC-245fa at pressures ranging from 0.15 MPa to 1.1 MPa (reduced pressure range: 0.04–0.31). Pool boiling experiments were conducted using horizontally oriented 1-cm2 heated surfaces to quantify the effects of pressure and a microporous-enhanced coating on heat transfer coefficients and critical heat flux (CHF) values. Results showed that the coating enhanced heat transfer coefficients and CHF by 430% and 50%, respectively. The boiling heat transfer performance of HFC-245fa was then compared with the boiling performance of HFC-134a and hydrofluoroolefin HFO-1234yf.

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Figures

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Fig. 1

High-pressure apparatus schematic

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Fig. 2

Test article three-dimensional computer-aided drawing (top) and cross-sectional view schematic (bottom)

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Fig. 3

Scanning electron microscope image of the 3M copper microporous coating

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Fig. 4

HFC-245fa pool boiling curves for a plain/smooth surface at various saturation temperatures/pressures. The arrows indicate the onset of CHF.

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Fig. 5

HFC-245fa pool boiling curves for microporous-coated surfaces at various pressures. A plain surface boiling curve is provided for reference.

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Fig. 6

HFC-245fa CHF values plotted versus pressure for plain and microporous surfaces. Error bars indicate the maximum and minimum values. In most cases, the error values are small and thus are hidden behind the data symbols.

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Fig. 7

Plain surface heat transfer coefficients versus heat flux for the three refrigerants. Results are for Tsat ≈ 50 °C. HFO-1234yf and HFC-134a data are from Ref. [1].

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Fig. 8

Plain surface heat transfer coefficients versus heat flux for the three refrigerants. Results are for Pred ≈ ⅓. HFO-1234yf and HFC-134a data are from Ref. [1].

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Fig. 9

Microporous surface heat transfer coefficients versus heat flux for the three refrigerants. Results are for Tsat ≈ 50 °C. HFO-1234yf and HFC-134a data are from Ref. [1].

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Fig. 10

CHF for the three refrigerants for plain and microporous surfaces plotted versus the reduced pressure. Error bars indicate the maximum and minimum values. HFO-1234yf and HFC-134a data are from Ref. [1].

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Fig. 11

The predicted CHF per Eq. (4) (b = 1.44, c = 0.53) versus the experimentally obtained CHF values for a plain surface. HFO-1234yf and HFC-134a data are from Ref. [1].

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Fig. 12

The predicted CHF per Eq. (3) (a = 1.85) versus the experimentally obtained CHF values for a microporous surface. HFO-1234yf and HFC-134a data are from Ref. [1].

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