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Research Papers: Evaporation, Boiling, and Condensation

Flow Boiling of R134a in Circular Microtubes—Part II: Study of Critical Heat Flux Condition

[+] Author and Article Information
Saptarshi Basu, Sidy Ndao, Yoav Peles

Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180

Gregory J. Michna

Department of Mechanical Engineering, South Dakota State University, Brookings, SD 57007

Michael K. Jensen1

Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180jensem@rpi.edu

1

Corresponding author.

J. Heat Transfer 133(5), 051503 (Feb 03, 2011) (9 pages) doi:10.1115/1.4003160 History: Received April 13, 2010; Revised December 01, 2010; Published February 03, 2011; Online February 03, 2011

A detailed experimental study was carried out on the critical heat flux (CHF) condition for flow boiling of R134a in single circular microtubes. The test sections had inner diameters (ID) of 0.50 mm, 0.96 mm, and 1.60 mm. Experiments were conducted over a large range of mass flux, inlet subcooling, saturation pressure, and vapor quality. CHF occurred under saturated conditions at high qualities and increased with increasing mass fluxes, tube diameters, and inlet subcoolings. CHF generally, but not always, decreases with increasing saturation pressures and vapor qualities. The experimental data were mapped to the flow pattern maps developed by Hasan [2005, “Two-Phase Flow Regime Transitions in Microchannels: A Comparative Experimental Study,” Nanoscale Microscale Thermophys. Eng., 9, pp. 165–182] and Revellin and Thome [2007, “A New Type of Diabatic Flow Pattern Map for Boiling Heat Transfer in Microchannels,” J. Micromech. Microeng., 17, pp. 788–796]. Based on these maps, CHF mainly occurred in the annular flow regime in the larger tubes. The flow pattern for the 0.50 mm ID tube was not conclusively identified. Four correlations—the Bowring correlation, the Katto-Ohno correlation, the Thome correlation, and the Zhang correlation—were used to predict the experimental data. The correlations predicted the correct experimental trend, but the mean absolute error (MAE) was high (>15%) A new correlation was developed to fit the experimental data with a MAE of 10%.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Wall temperature variations at different heat fluxes for din=0.50 mm at Psat=670 kPa, G=1500 kg/m2 s, and ΔTsubcooling=20°C

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Figure 2

Effect of mass flux and tube size on CHF for Psat=1160 kPa and ΔTsubcooling=5°C

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Figure 3

Effect of saturation pressure on CHF for din=0.50 mm ID tube with ΔTsub=5°C

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Figure 4

Effect of inlet subcooling on CHF for din=1.60 mm and G=600 kg/m2 s

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Figure 5

Effect of exit quality on CHF for din=0.96 mm and ΔTsubcooling=5°C

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Figure 6

Effect of exit quality on CHF for din=0.50 mm and ΔTsubcooling=20°C

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Figure 7

Experimental R134a data mapped on the flow map developed by Hasan (22)

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Figure 8

Experimental R134a data mapped on the flow map developed by Revellin and Thome (23)

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Figure 9

Comparison of experimental CHF data for d=1.60 mm with predictions of the correlations at Psat=890 kPa and ΔTsubcooling=5°C

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Figure 10

Comparison of experimental CHF data with predictions of the new correlation

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Figure 11

Comparison of experimental R123 CHF data of Roday and Jensen (2) with predictions of the new correlation

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