Study on the Pool Boiling Bubble Departure Diameter and Frequency from Porous Graphite Foam Structures

This paper presents an experimental study of heat transfer in a pool boiling evaporator with porous insert. Porous graphite foams of different structures were tested with FC-72 and HFE-7000 coolants with the objective of maximizing the heat transfer in a pool boiling configuration. A two-phase thermosyphon facility was developed to investigate the system performance using graphite foams of block and fin structures. The effects of foam configuration, working fluid type and coolant filling volume on heater surface temperature and superheat were analyzed. The results showed that coolant filling volume has negligible effect on the cooling performance. On the other hand, the thermosyphon performance is significantly affected by the coolant properties and the configuration of the porous graphite foam. A comparison of the Bond numbers obtained for FC-72 and HFE-7000 indicates that the bubbles have to overcome higher surface tension forces before departing the foam surface in HFE-7000. Meanwhile, the effect of foam configuration on the boiling heat transfer performance implies that a properly designed geometry of porous graphite foam will lead to significant enhancement of the evaporation process in a thermosyphon system.

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Experimental Study of a Two-Phase Thermosyphon With Porous Graphite Foam Insert

Journal of Thermal Science and Engineering Applications ◽

10.1115/1.4003885 ◽

2011 ◽

Vol 3 (2) ◽

Cited By ~ 6

Author(s):

L. W. Jin ◽

K. C. Leong ◽

I. Pranoto ◽

H. Y. Li ◽

J. C. Chai

Keyword(s):

Heat Transfer ◽

Experimental Study ◽

Boiling Heat Transfer ◽

Pool Boiling ◽

Working Fluid ◽

Two Phase ◽

Filling Volume ◽

Porous Graphite ◽

Surface Tension Forces ◽

Graphite Foam

This paper presents an experimental study of heat transfer in a pool boiling evaporator with porous insert. Porous graphite foams were structured into cubic block and straight fin shapes and tested with FC-72 and HFE-7000 coolants with the objective of maximizing the heat transfer in a pool boiling configuration. A two-phase thermosyphon facility was developed to investigate the system’s performance using graphite foams of block and fin structures. The effects of foam configuration, working fluid type, and coolant filling volume on pool boiling heat transfer were analyzed. The results showed that the coolant filling volume has negligible effect on cooling performance. On the other hand, the thermosyphon performance is significantly affected by the coolant properties and the configuration of the porous graphite foam. A comparison of the Bond numbers obtained for FC-72 and HFE-7000 indicates that the bubbles have to overcome higher surface tension forces before departing the foam surface in HFE-7000. Meanwhile, the effect of the foam configuration on the boiling heat transfer performance implies that a properly designed geometry of the porous graphite foam will lead to significant enhancement of the evaporation process in a thermosyphon system.

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Experimental Investigation of a Thermosyphon With Microstructure on the Boiling Surface

Journal of Thermal Science and Engineering Applications ◽

10.1115/1.4041442 ◽

2018 ◽

Vol 11 (1) ◽

Author(s):

Y. Chai ◽

W. Tian ◽

J. Tian ◽

L. W. Jin ◽

X. Z. Meng ◽

...

Keyword(s):

Heat Transfer ◽

Heat Dissipation ◽

Pool Boiling ◽

High Heat ◽

Primary Concern ◽

Heat Transfer Efficiency ◽

Heater Wall ◽

Micro Structures ◽

Thermal Physical Properties ◽

Graphite Foam

Abstract In recent years, a primary concern in the development of electronic technology is high heat dissipation of power devices. The advantages of unique thermal physical properties of graphite foam raise up the possibility of developing pool boiling system with better heat transfer efficiency. A compact thermosyphon was developed with graphite foam insertions to explore how different parameters affect boiling performance. Heater wall temperature, superheat, departure frequency of bubbles, and thermal resistance of the system were analyzed. The results indicated that the boiling performance is affected significantly by thermal conductivity and pore diameter of graphite foam. A proposed heat transfer empirical correlation reflecting the relations between graphite foam micro structures and pool boiling performance of Novec7100 was developed in this paper.

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Experimental Study of Enhanced Pool Boiling Heat Transfer Using Graphite Foam Inserts

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.312-315.352 ◽

2011 ◽

Vol 312-315 ◽

pp. 352-357 ◽

Cited By ~ 1

Author(s):

K.C. Leong ◽

L.W. Jin ◽

I. Pranoto ◽

H.Y Li ◽

J.C. Chai

Keyword(s):

Heat Transfer ◽

Experimental Study ◽

Boiling Heat Transfer ◽

High Speed ◽

Bubble Formation ◽

Pool Boiling ◽

Heat Fluxes ◽

Copper Block ◽

Different Types ◽

Graphite Foam

This paper presents the results of an experimental study of heat transfer in a pool boiling evaporator with porous insert. Different types of graphite foams were tested with the phase change coolant FC-72 in a designed thermosyphon. Comparisons between the graphite foams and a solid copper block show that the porous structure enhances pool boiling significantly. The boiling thermal resistance of the tested graphite foams was found to be about 2 times lower than that of the copper block. The bubble formation recorded by a high speed camera indicates that boiling from a graphite foam is more vigorous than from a copper block. The designed thermosyphon with graphite foam insert can remove heat fluxes of up to 112 W/cm2 with the maximum heater temperature maintained below 100°C.

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Synchrotron X-ray Diffraction Studies of Multilayer Nitrogen Physisorbed on Porous Graphite Foam

Langmuir ◽

10.1021/la9807560 ◽

1999 ◽

Vol 15 (4) ◽

pp. 1423-1428 ◽

Cited By ~ 4

Author(s):

T. E. Burns ◽

J. R. Dennison ◽

S. N. Ehrlich

Keyword(s):

X Ray Diffraction ◽

X Ray ◽

Porous Graphite ◽

Graphite Foam

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Pool Boiling in Saturated and Subcooled FC-72 Dielectric Fluid From a Porous Graphite Surface

Heat Transfer, Volume 2 ◽

10.1115/imece2004-59905 ◽

2004 ◽

Cited By ~ 9

Author(s):

Mohamed S. El-Genk ◽

Jack L. Parker

Keyword(s):

Heat Flux ◽

Pool Boiling ◽

Nucleate Boiling ◽

Heat Fluxes ◽

Porous Coating ◽

Dielectric Fluid ◽

Subcooled Boiling ◽

Porous Graphite ◽

Rate Of Increase ◽

Boiling Incipience

Experiments are conducted that investigated pool boiling of FC-72 liquid at saturation and 10, 20, and 30 K subcooling on porous graphite and smooth copper surfaces measuring 10 × 10 mm. The nucleate boiling heat flux, Critical Heat Flux (CHF), and surface superheats at boiling incipience are compared. Theses heat fluxes are also compared with those of other investigators for smooth copper and silicon, etched SiO2, surfaces and micro-porous coating. No temperature excursion at boiling incipience on the porous graphite that occurred at a surface superheats of < 1.0 K. Conversely, the temperature excursions of 24.0 K and 12.4–17.8 K are measured at incipient boiling in saturation and subcooled boiling on copper. Nucleate boiling heat fluxes on porous graphite are significantly higher and corresponding surface superheats are much smaller than on copper. CHF on porous graphite (27.3, 39.6, 49.0, and 57.1 W/cm2 in saturation and 10 K, 20 K, and 30 K subcooled boiling, respectively) are 61.5%–207% higher than those on copper (16.9, 19.5, 23.6, and 28.0 W/cm2, respectively). The surface superheats at CHF on the porous graphite of 11.5 K in saturation and 17–20 K in subcooled boiling are significantly lower that those on copper (25 K and 26–28 K, respectively). In addition, the rate of increase of CHF on porous graphite with increased subcooling is ~ 125% higher than that on copper.

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Effect of Inclination on Pool Boiling of FC-72 Dielectric Liquid on Porous Graphite

Heat Transfer: Volume 4 ◽

10.1115/ht2005-72289 ◽

2005 ◽

Cited By ~ 4

Author(s):

Jack L. Parker ◽

Mohamed S. El-Genk

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Inclination Angle ◽

Boiling Heat Transfer ◽

Pool Boiling ◽

Nucleate Boiling ◽

Porous Graphite ◽

Nucleate Boiling Heat Transfer ◽

Boiling Heat Transfer Coefficient

Saturation pool boiling experiments of FC-72 liquid on a flat, porous graphite and smooth copper surfaces measuring 10 × 10 mm investigated the effect of surface orientation on nucleate boiling and Critical Heat Flux (CHF). The inclination angle of the surface increased from 0° (upward-facing) to 60°, 90°, 120°, 150°, and 180° (downward facing). Results demonstrated significant increases in the nucleate boiling heat transfer coefficient and CHF on porous graphite, compared to those on copper. At low surface superheats, increasing the inclination angle increases the nucleate boiling heat transfer coefficient, which decreases with increased inclination angle at high surface superheats. These results and the measured decreases of CHF with increased inclination angle are consistent with those reported earlier by other investigators for dielectric and non-dielectric liquids. On smooth surfaces and micro-porous coatings, the reported fractional decreases in CHF with increased inclination angle are almost identical, but markedly larger than those measured in this work on porous graphite. On these surfaces the reported CHF in the downward-facing position (180° inclination) is ∼10–20% of that in the upward-facing position (0° inclination), compared to ∼53.3% on porous graphite. The CHF values of FC-72 liquid on porous graphite, which also decreased with increased inclination angle, are correlated using the general form suggested by Kutatelatze (1961) to within ± 5% of the experimental data.

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