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Research Papers

Pool Boiling Heat Transfer Characteristics of HFO-1234yf on Plain and Microporous-Enhanced Surfaces

[+] Author and Article Information
Gilberto Moreno

e-mail: gilbert.moreno@nrel.gov

Charles King

National Renewable Energy Laboratory,
Golden, CO 80401

Contributed by the Heat Transfer Division of ASME for publication in the Journal of Heat Transfer. Manuscript received June 29, 2012; final manuscript received January 18, 2013; published online September 23, 2013. Assoc. Editor: Sujoy Kumar Saha.

J. Heat Transfer 135(11), 111014 (Sep 23, 2013) (10 pages) Paper No: HT-12-1330; doi: 10.1115/1.4024622 History: Received June 29, 2012; Revised January 18, 2013

This study characterizes the pool boiling performance of HFO-1234yf (hydrofluoroolefin 2,3,3,3-tetrafluoropropene). HFO-1234yf is a new, environmentally friendly refrigerant likely to replace HFC-134a in automotive air-conditioning systems. Pool boiling experiments were conducted at system pressures ranging from 0.7 to 1.7 MPa using horizontally oriented 1-cm2 heated surfaces. Test results for pure (oil-free) HFO-1234yf and HFC-134a were compared. The results showed that the boiling heat transfer coefficients of HFO-1234yf and HFC-134a were nearly identical at lower heat fluxes. HFO-1234yf yielded lower heat transfer coefficients at higher heat fluxes and lower critical heat flux (CHF) values as compared with HFC-134a. To enhance boiling heat transfer, a copper microporous coating was applied to the test surfaces. The coating enhanced both the boiling heat transfer coefficients and CHF for both refrigerants at all tested pressures. Increasing pressure decreased the level of heat transfer coefficient enhancements and increased the level of CHF enhancements. The experimental data were then used to develop a correlation for predicting the CHF for a smooth/plain heated surface.

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Figures

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Fig. 1

High pressure apparatus schematic

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Fig. 2

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

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Fig. 3

Scanning electron microscope image of the copper microporous coating

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Fig. 4

HFC-134a pool boiling curves for a baseline surface at various saturation temperatures. Arrows denote the onset of CHF.

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Fig. 5

HFC-134a pool boiling curves for a microporous coated surface at various saturation temperatures

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Fig. 6

HFC-134a boiling heat transfer coefficient enhancement from the microporous coating plotted versus heat flux

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Fig. 7

HFC-134a CHF values for the baseline and microporous surfaces plotted versus pressure. Data points are an average based on test repetitions. Error bars indicate maximum and minimum values.

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Fig. 8

HFO-1234yf pool boiling curves for a baseline surface at various saturation temperatures

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Fig. 9

HFO-1234yf pool boiling curves for a microporous coated surface at various saturation temperatures

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Fig. 10

HFO-1234yf boiling heat transfer coefficient enhancement from the microporous coating plotted versus heat flux

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Fig. 11

HFO-1234yf CHF values for the baseline and microporous coated surfaces plotted versus pressure. Data points are an average based on test repetitions. Error bars indicate maximum and minimum values.

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Fig. 12

CHF predicted values per Eq. (2) plotted versus the experimentally obtained CHF values

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Fig. 13

HFO-1234yf and HFC-134a heat transfer coefficients for (a) baseline surfaces and (b) microporous coated surfaces

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Fig. 14

HFO-1234yf CHF over HFC-134a CHF ratio plotted versus the saturation temperature for the baseline and microporous surfaces

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