Effect of pore number density on nucleate boiling heat transfer performance of aluminum surface with microporous structure

Numerous researches have been developed for pool boiling on microporous coated surface in the past decade. The nucleate boiling heat transfer was found to be increased by up to 4.5 times than that on uncoated surface. Recently, the two-phase micro heat exchangers have been considered for high flux electronic devices cooling. The enhancement techniques for improving the nucleate boiling heat transfer performance in the micro heat exchangers have gotten more importance. Previous studies of microporous coatings, however, have been restricted to boiling in unconfined space. No studies have been made on the feasibility of using microporous coatings for enhancing boiling in confined spaces. This study provides an experimental observation of the vapor generation and leaving processes on microporous coatings surface in a 1-mm confined space. It would be helpful for understanding the mechanism of boiling heat transfer and improving the design of two-phase micro heat exchangers. Aluminum particles of average diameter 20 μm were mixed with a binder and a carrier to develop a 150 μm thickness boiling enhancement paint on a 3.0 cm by 3.0 cm copper heating surface. The heating surface was covered by a thin glass plate with a 1 mm spacer to form a 1 mm vertical narrow space for the test section. The boiling phenomenon was recorded by a high speed camera. In addition to the three boiling regimes observed by Bonjour and Lallemand [1], i.e., isolated deformed bubbles, coalesced bubbles and partial dryout at low, moderate and high heat fluxes respectively in unconfined space, a suction and blowing process was observed at the highest heat flux condition. Owing to the space confinement, liquid was sucked and vapor was expelled periodically during the bubble generation process. This mechanism significantly enhanced the boiling heat transfer performance in confined space.

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Pool Boiling Heat Transfer with Nanotube Arrays Surface on Titanium

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.550-553.2913 ◽

2012 ◽

Vol 550-553 ◽

pp. 2913-2916 ◽

Cited By ~ 1

Author(s):

Jin Liang Tao ◽

Xin Liang Wang ◽

Pei Hua Shi ◽

Xiao Ping Shi

Keyword(s):

Heat Transfer ◽

Boiling Heat Transfer ◽

Heat Transfer Performance ◽

Pool Boiling ◽

Nucleate Boiling ◽

Test Fluid ◽

Porous Coating ◽

Pool Boiling Heat Transfer ◽

Nucleate Boiling Heat Transfer ◽

Boiling Heat Transfer Coefficient

In this paper, a new porous coating was formed directly on the surface of titanium metal via anodic oxidation. And by the SEM, the morphology of the coating, which is composed of well-ordered perpendicular nanotubes, was characterized. Moreover, taking deionized water as the test fluid, a visualization study of the coating on its pool boiling heat transfer performance was made. The results demonstrated that compared with the smooth surface, the nucleate boiling heat transfer coefficient can increase 3 times while the nucleate boiling super heat was reduced 30%.

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Effect of Pressure, Subcooling, and Dissolved Gas on Pool Boiling Heat Transfer From Microporous Surfaces in FC-72

Journal of Heat Transfer ◽

10.1115/1.1527890 ◽

2003 ◽

Vol 125 (1) ◽

pp. 75-83 ◽

Cited By ~ 74

Author(s):

K. N. Rainey ◽

S. M. You ◽

S. Lee

Keyword(s):

Heat Transfer ◽

Boiling Heat Transfer ◽

Heat Transfer Performance ◽

Nucleate Boiling ◽

Gas Content ◽

Absolute Pressure ◽

Dissolved Gas ◽

Test Conditions ◽

Nucleate Boiling Heat Transfer ◽

Surface Correlations

The present research is an experimental study of the effects of pressure, subcooling, and non-condensable gas (air) on the pool nucleate boiling heat transfer performance of a microporous enhanced and a plain (machine-roughened) reference surface. The test surfaces, 1-cm2 flat copper blocks in the horizontal, upward facing orientation, were immersed in FC-72. The test conditions included an absolute pressure range of 30–150 kPa, a liquid subcooling range of 0 (saturation) to 50 K, and both gas-saturated and pure subcooling conditions. Effects of these parameters on nucleate boiling and critical heat flux (CHF) were investigated. Results showed that, in general, the effects of pressure and subcooling on both nucleate boiling and CHF were consistent with the prevailing trends in the literature. For the present heater geometry, the effects of dissolved gas on the boiling performance were generally small, however, as the dissolved gas content increased (through either increased pressure or subcooling) more of the nucleate boiling curve was affected (enhanced). The enhancement of CHF from increased liquid subcooling was greater for the microporous surface than the plain surface. Correlations for both nucleate boiling and CHF were also presented.

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