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RESEARCH PAPERS: Evaporation, Boiling, and Condensation

Parametric Study of Pool Boiling on Horizontal Highly Conductive Microporous Coated Surfaces

[+] Author and Article Information
Chen Li

Department of Mechanical Engineering, University of Colorado at Boulder, Boulder, CO 80309-0427lichen.cu@colorado.edu

G. P. Peterson

Department of Mechanical Engineering, University of Colorado at Boulder, Boulder, CO 80309-0427bud.peterson@colorado.edu

J. Heat Transfer 129(11), 1465-1475 (Apr 10, 2007) (11 pages) doi:10.1115/1.2759969 History: Received January 02, 2006; Revised April 10, 2007

To better understand the mechanisms that govern the behavior of pool boiling on horizontal highly conductive microporous coated surfaces, a series of experimental investigations were designed to systematically examine the effects of the geometric dimensions (i.e., coating thickness, volumetric porosity, and pore size, as well as the surface conditions of the porous coatings) on the pool-boiling performance and characteristics. The study was conducted using saturated distilled water at atmospheric pressure (101kPa) and porous surfaces fabricated from sintered isotropic copper wire screens. For nucleate boiling on the microporous coated surfaces, two vapor ventilation modes were observed to exist: (i) upward and (ii) mainly from sideways leakage to the unsealed sides and partially from the center of porous surfaces. The ratio of the heater size to the coating thickness, the friction factor of the two-phase flow to single-phase flow inside the porous coatings, as well as the input heat flux all govern the vapor ventilation mode that occurs. In this investigation, the ratio of heater size to coating thickness varies from 3.5 to 38 in order to identify the effect of heater size on the boiling characteristics. The experimental results indicate that the boiling performance and characteristics are also strongly dependent on the volumetric porosity and mesh size, as well as the surface conditions when the heater size is given. Descriptions and discussion of the typical boiling characteristics; the progressive boiling process, from pool nucleate boiling to film boiling; and the boiling performance curves on conductive microporous coated surfaces are all systematically presented.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Scanning Electron Microscope (SEM) images of sintered isotropic copper mesh with 1509m−1(145in.−1), 56μm(0.0022in.) wire diameter, fabricated at a sintering temperature of 1030°C with gas mixture protection (75% N2 and 25% H2) for 2h(19): (a) Top view of staggered sintered isotropic copper mesh (19), (b) top view of inline stacked sintered isotropic copper mesh (19), and (c) side view of compact sintered isotropic copper mesh (20)

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Figure 2

Schematic of the test article

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Figure 3

Image of the completed sintered wire screen surface before the test and after dryout

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Figure 4

Schematic of the test facility

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Figure 5

(a) Relationship between the heat flux and wall superheat based on the heater area as a function of thickness, (b) logarithmic relationship between the heat flux based on the heater area and wall superheat as a function of thickness, (c) relationship between the heat transfer coefficient and heat flux curve, based on the heater area as a function of thickness, and (d) relationship between boiling heat transfer performance and porous coating thickness

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Figure 6

Vapor film thickness as a function of heat flux at the heated wall

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Figure 7

(a) Logarithmic relationship between the heat flux based on the heater area and the wall superheat as a function of mesh size and (b) relationship between the heat transfer coefficient and heat flux based on the heater area as a function of mesh size

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Figure 8

(a) Logarithmic relationship between the heat flux based on the heater area and wall superheat as a function of volumetric porosity, (b) relationship between the heat transfer coefficient and heat flux curve based on the heater area as a function of mesh size, and (c) multiple boiling incipience phenomenon inside a porous media with low volumetric porosity

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Figure 9

Effects of surface conditions on boiling performance and characteristics for pool boiling in porous coated surfaces

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Figure 10

Boiling and flow regimes in microconductive porous coated surfaces

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