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Research Papers: Evaporation, Boiling, and Condensation

Quantitative Evaluation of the Dependence of Pool Boiling Heat Transfer Enhancement on Sintered Particle Coating Characteristics

[+] Author and Article Information
Suchismita Sarangi, Justin A. Weibel, Suresh V. Garimella

School of Mechanical Engineering;Birck Nanotechnology Center,
Purdue University,
585 Purdue Mall,
West Lafayette, IN 47907

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received April 12, 2016; final manuscript received September 16, 2016; published online November 8, 2016. Assoc. Editor: Debjyoti Banerjee.

J. Heat Transfer 139(2), 021502 (Nov 08, 2016) (13 pages) Paper No: HT-16-1194; doi: 10.1115/1.4034901 History: Received April 12, 2016; Revised September 16, 2016

Immersion cooling strategies often employ surface enhancements to improve the pool boiling heat transfer performance. Sintered particle/powder coatings have been commonly used on smooth surfaces to reduce the wall superheat and increase the critical heat flux (CHF). However, there is no unified understanding of the role of coating characteristics on pool boiling heat transfer enhancement. The morphology and size of the particles affect the pore geometry, permeability, thermal conductivity, and other characteristics of the sintered coating. In turn, these characteristics impact the heat transfer coefficient and CHF during boiling. In this study, pool boiling of FC-72 is experimentally investigated using copper surfaces coated with a layer of sintered copper particles of irregular and spherical morphologies for a range of porosities (∼40–80%). Particles of the same effective diameter (90–106 μm) are sintered to yield identical coating thicknesses (∼4 particle diameters). The porous structure formed by sintering is characterized using microcomputed tomography (μ-CT) scanning to study the geometric and effective thermophysical properties of the coatings. The boiling performance of the porous coatings is analyzed. Coating characteristics that influence the boiling heat transfer coefficient and CHF are identified and their relative strength of dependence analyzed using regression analysis. Irregular particles yield higher heat transfer coefficients compared to spherical particles at similar porosity. The coating porosity, pore diameter, unit necking area, unit interfacial area, effective thermal conductivity, and effective permeability are observed to be the most critical coating properties affecting the boiling heat transfer coefficient and CHF.

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Figures

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Fig. 1

Schematic diagram of test facility with inset showing a photograph of a copper block coated with spherical sintered particles

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Fig. 2

SEM images of (a) spherical and (b) irregular coatings at a low, intermediate, and high porosity, showing the pore structure of the coatings

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Fig. 3

Image processing steps showing (a) raw 2D slice from μ-CT scan, (b) 3D reconstructed volume, (c) 2D slice showing pore domain (lighter region) and copper regions after thresholding, (d) segmented pore domain, (e) segmented copper domain, and (f) 3D reconstructed volume segmentation in both pore and copper domains. An overall domain size of 800 μm × 800 μm × 207 μm for the spherical particle coating at 39% porosity is shown.

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Fig. 4

Three-dimensional reconstructed solid domain (after thresholding) for (a) spherical and (b) irregular coatings at a low, intermediate, and high porosity

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Fig. 5

Meshed domain (340 μm × 340 μm × 207 μm) for the spherical particle coating at 39% porosity is shown

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Fig. 6

Boundary conditions for (a) conduction through copper and pore domains and (b) flow through the pore domain, used to obtain the effective conductivity and effective permeability, respectively

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Fig. 7

Boiling curves of area-averaged heat flux versus wall superheat, ΔT (Ts − Tsat), for (a) spherical and (b) irregular particle coatings. Occurrence of CHF is indicated by horizontal arrows.

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Fig. 8

Heat transfer coefficient versus area-averaged heat flux for (a) spherical and (b) irregular particle coatings

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Fig. 9

Representative contours of (a) pressure field in the pore domain, (b) temperature field in the solid domain, and (c) temperature field in the pore domain for the spherical particle coating at 39% porosity. The corresponding contours for irregular particle coatings at 66% porosity are shown in (d–f). The contours are obtained from numerical simulation of the effective permeability and effective thermal conductivity.

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Fig. 10

Heat transfer coefficient versus normalized critical coating properties for (a) spherical and (b) irregular particle coatings. Each input property is normalized by its maximum value. The symbols indicate experimental data points, while the dotted lines indicate a linear fit to the data.

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