Non-uniform wall temperature distribution of nucleate boiling heat transfer in helically coiled tubes

In the past three decades, fractal geometry and technique have received considerable attention due to its wide applications in sciences and technologies such as in physics, mathematics, geophysics, oil recovery, material science and engineering, flow and heat and mass transfer in porous media etc. The fractal geometry and technique may become particularly powerful when they are applied to deal with random and disordered media such as porous media, nanofluids, nucleate boiling heat transfer. In this paper, a summary of recent advances is presented in the areas of heat and mass transfer in fractal media by fractal geometry technique. The present overview includes a brief summary of the fractal geometry technique applied in the areas of heat and mass transfer; thermal conductivities of porous media and nanofluids; nucleate boiling heat transfer. A few comments are made with respect to the theoretical studies that should be made in the future.

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Visualization of Boiling Heat Transfer on Micro Porous Coated Surface in Confined Space

ASME 2013 11th International Conference on Nanochannels, Microchannels, and Minichannels ◽

10.1115/icnmm2013-73175 ◽

2013 ◽

Author(s):

Chien-Yuh Yang ◽

Chien-Fu Liu

Keyword(s):

Heat Transfer ◽

Heat Exchangers ◽

Boiling Heat Transfer ◽

Heat Transfer Performance ◽

Heating Surface ◽

Nucleate Boiling ◽

Confined Space ◽

Two Phase ◽

Nucleate Boiling Heat Transfer ◽

Coated Surface

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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