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Research Papers

Flow Boiling Heat Transfer in Horizontal Metal-Foam Tubes

[+] Author and Article Information
C. Y. Zhao1

School of Engineering, University of Warwick, Coventry CV4 7AL, UKc.y.zhao@warwick.ac.uk

W. Lu

School of Engineering, University of Warwick, Coventry CV4 7AL, UK

S. A. Tassou

School of Engineering and Design, Brunel University, Uxbridge, Middlesex UB8 3PH, UK

1

Corresponding author.

J. Heat Transfer 131(12), 121002 (Oct 15, 2009) (8 pages) doi:10.1115/1.3216036 History: Received August 16, 2007; Revised October 20, 2008; Published October 15, 2009

The two-phase flow and boiling heat transfer in horizontal metal-foam filled tubes are experimentally investigated. The results show that the heat transfer is almost doubled by reducing the cell size from 20 ppi to 40 ppi for a given porosity, thanks to more surface area and strong flow mixing for the smaller cell size. The boiling heat transfer coefficient keeps steady rising, albeit slowly, by increasing the vapor quality for high mass flow rates, while the same story does not hold for the cases of low mass flow rates. The flow pattern can be indirectly judged through monitoring the cross-sectional wall surface temperature fluctuations and wall-refrigerant temperature difference. As the operating pressure increases, the boiling heat transfer at low vapor quality (x<0.1) exhibits similar behavior with pool boiling heat transfer, namely, the heat transfer is enhanced by improving the pressure. However the flow boiling heat transfer is suppressed to some extent as the pressure increases. The heat transfer coefficient of copper foam tubes is approximately three times higher than that of plain tubes.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic diagram of the test rig

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Figure 3

Variation in the pressure drop per unit length as a function of the vapor quality

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Figure 4

Effect of metal-foam cell size on the pressure drop

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Figure 5

Variation in the pressure drop as a function of the mass flow rate

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Figure 6

Effect of operating pressure on the pressure drop

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Figure 7

Wall temperature’s fluctuations with time for vapor quality at (a) x=0.18 and (b) x=0.53 for the mass flow rate of 26 kg/m2 s

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Figure 8

Wall temperature’s fluctuations for vapor quality at (a) x=0.22 and (b) x=0.63 for the high mass flow rate of 106 kg/m2 s

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Figure 9

Temperature difference between the wall surface and refrigerant for two different mass flow rates

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Figure 10

Variation in the heat transfer coefficient with the vapor quality for two different cell-sized foam tubes

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Figure 11

Effect of cell size on boiling heat transfer: (a) for different vapor qualities and (b) for different mass flow rates

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Figure 12

Effect of heat flux on boiling heat transfer

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Figure 13

Effect of refrigerant pressure on boiling heat transfer

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Figure 14

Comparison of heat transfer between the two different material foam tubes

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Figure 15

Comparison of heat transfer coefficient between plain and copper foam tubes

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