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Record Details

Record 49 of 9601
Heat Transfer Performances of Pool Boiling on Metal-Graphite Composite Surfaces
Author and Affiliation:
Zhang, Nengli(Ohio Aerospace Inst., Cleveland, OH United States)
Chao, David F.(NASA Glenn Research Center, Cleveland, OH United States)
Yang, Wen-Jei(Michigan Univ., Dept. of Mechanical Engineering and Applied Mechanics, Ann Arbor, MI United States)
Abstract: Nucleate boiling, especially near the critical heat flux (CHF), can provide excellent economy along with high efficiency of heat transfer. However, the performance of nucleate boiling may deteriorate in a reduced gravity environment and the nucleate boiling usually has a potentially dangerous characteristic in CHF regime. That is, any slight overload can result in burnout of the boiling surface because the heat transfer will suddenly move into the film-boiling regime. Therefore, enhancement of nucleate boiling heat transfer becomes more important in reduced gravity environments. Enhancing nucleate boiling and critical heat flux can be reached using micro-configured metal-graphite composites as the boiling surface. Thermocapillary force induced by temperature difference between the graphite-fiber tips and the metal matrix, which is independent of gravity, will play an important role in bubble detachment. Thus boiling heat transfer performance does not deteriorate in a reduced-gravity environment. Based on the existing experimental data, and a two-tier theoretical model, correlation formulas are derived for nucleate boiling on the copper-graphite and aluminum-graphite composite surfaces, in both the isolated and coalesced bubble regimes. Experimental studies were performed on nucleate pool boiling of pentane on cooper-graphite (Cu-Gr) and aluminum-graphite (Al-Gr) composite surfaces with various fiber volume concentrations for heat fluxes up to 35 W per square centimeter. It is revealed that a significant enhancement in boiling heat transfer performance on the composite surfaces is achieved, due to the presence of micro-graphite fibers embedded in the matrix. The onset of nucleate boiling (the isolated bubble regime) occurs at wall superheat of about 10 C for the Cu-Gr surface and 15 C for the Al-Gr surface, much lower than their respective pure metal surfaces. Transition from an isolated bubble regime to a coalesced bubble regime in boiling occurs at a superheat of about 14 C on Cu-Gr surface and 19 C on Al-Gr surface.
Publication Date: Dec 01, 2000
Document ID:
20010024996
(Acquired Mar 30, 2001)
Subject Category: FLUID MECHANICS AND THERMODYNAMICS
Document Type: Conference Paper
Publication Information: Proceedings of the Fifth Microgravity Fluid Physics and Transport Phenomena Conference; 1459-1461; (SEE 20010024890)
Financial Sponsor: NASA Glenn Research Center; Cleveland, OH United States
Organization Source: NASA Glenn Research Center; Cleveland, OH United States
Description: 3p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: No Copyright
NASA Terms: HEAT TRANSFER; NUCLEATE BOILING; MATHEMATICAL MODELS; MICROGRAVITY; METAL MATRIX COMPOSITES; METAL SURFACES; HEAT FLUX; THERMOCAPILLARY MIGRATION; ALUMINUM GRAPHITE COMPOSITES; BUBBLES; COPPER
Availability Notes: Abstract Only; Available from STI Support Services only as part of the entire parent document
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