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Research Papers: Evaporation, Boiling, and Condensation

Experimental Study of Horizontal Flow Boiling Heat Transfer of R134a at a Saturation Temperature of 18.6 °C

[+] Author and Article Information
Carlos A. Dorao

Department of Energy and Process Engineering,
Norwegian University of Science
and Technology,
Trondheim 7491, Norway
e-mail: carlos.dorao@ntnu.no

Oscar Blanco Fernandez

ETSII,
University in Madrid,
Madrid 28006, Spain

Maria Fernandino

Department of Energy and Process Engineering,
Norwegian University of Science
and Technology,
Trondheim 7491, Norway

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received October 12, 2016; final manuscript received June 17, 2017; published online July 25, 2017. Assoc. Editor: Joel L. Plawsky.

J. Heat Transfer 139(11), 111510 (Jul 25, 2017) (11 pages) Paper No: HT-16-1656; doi: 10.1115/1.4037153 History: Received October 12, 2016; Revised June 17, 2017

In spite of the extensive work in flow boiling in small-diameter tubes, the general characteristics and dominant mechanisms remain elusive. In this study, flow boiling heat transfer of R134a inside a 5 mm I.D., smooth horizontal stainless steel pipe is experimentally studied. Local heat transfer coefficients (HTCs) were measured for heat fluxes from 3.9 to 47 kW/m2 and mass fluxes from 200 to 400 kg/m2 s at a saturation temperature of 18.6 °C. The studied cases have shown different behaviors at low and high heat fluxes. At low heat fluxes, the convective contribution looks to control the HTC, while at high heat fluxes the nucleation of vapor looks to be the dominant mechanism. Reducing the heat flux, the HTC approaches asymptotically a limit equivalent to the single-phase HTC defined in terms of the sum of the superficial liquid and vapor Reynolds numbers. A new correlation for dominant convective flow boiling is proposed and evaluated against experimental data from the literature.

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References

Figures

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Fig. 1

Summary of some studies on flow boiling in horizontal tubes with R134a and diameter between 3 and 15 mm

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Fig. 2

Summary of some studies on flow boiling in horizontal tubes with R134a and diameter between 3 and 15 mm

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Fig. 3

Sketch of the test facility

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Fig. 4

Sketch of the heated test section

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Fig. 5

Histogram of the fluid and wall temperature for a data point corresponding to 120 s of data logging

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Fig. 6

Nonequilibrium effect at low thermodynamic qualities

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Fig. 7

Single-phase liquid and vapor HTC measurement and prediction by Dittus–Boelter correlation

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Fig. 8

Comparison of the two-phase flow HTC to a similar case from the literature

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Fig. 9

Test of repeatability of the HTC

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Fig. 10

Effect of the heat flux on the local HTC for a fixed mass flux

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Fig. 11

Comparison of HTC at two different heat fluxes

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Fig. 12

Dependency of the superficial liquid Reynolds number on the Nu

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Fig. 13

Dependency of the superficial vapor Reynolds number on the Nu

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Fig. 14

Dependency of the sum of the superficial liquid and vapor Reynolds number on the Nu

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Fig. 15

Evaluation of the model in terms of ReL+ReV

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Fig. 16

Evaluation of the model in terms of the thermodynamic quality

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Fig. 17

Evaluation of the model of Gungor and Winterton [18] in terms of the thermodynamic quality

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Fig. 18

Dependency of the dominant flow convection model from Gungor and Winterton [18] in terms of the Re2ϕ

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