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TECHNICAL BRIEF

Pool Boiling Experiments on Multiwalled Carbon Nanotube (MWCNT) Forests

[+] Author and Article Information
Hee Seok Ahn, Nipun Sinha, Debjyoti Banerjee

Mechanical Engineering Department, Texas A&M University, College Station, TX 77843-3123

Mei Zhang, Shaoli Fang, Ray H. Baughman

NanoTech Institute and Department of Chemistry, University of Texas at Dallas, Richardson, TX 75083

J. Heat Transfer 128(12), 1335-1342 (May 29, 2006) (8 pages) doi:10.1115/1.2349511 History: Received November 08, 2005; Revised May 29, 2006

In this study, two silicon wafer substrates were coated with vertically aligned multiwalled carbon nanotubes (MWCNT) “forests” and were used for pool boiling studies. The MWCNT forests (9 and 25μm in height) were synthesized on the silicon wafer substrates using chemical vapor deposition (CVD) process. The substrates were clamped on a cylindrical copper block with embedded cartridge heaters. The heat flux was measured using sheathed K-type thermocouples, which were placed inside the cylindrical copper block. Pool boiling experiments using refrigerant PF-5060 as the working liquid were conducted to obtain the pool “boiling curve.” The experiments were conducted in nucleate and film boiling regimes to investigate the effect of MWCNT height on pool boiling performance. Reference (control) experiments were also performed with an atomically smooth bare silicon wafer (without MWCNT coating). The results show that the MWCNT forests enhanced critical heat flux (CHF) by 2528% compared to control experiments. For the film boiling regime, Type-B MWCNT (25μm in height) yields 57% higher heat flux at Leidenfrost point (film boiling regime) compared to control experiments. However, for the Type-A MWCNT (9μm in height) the film boiling heat flux values are nearly identical to the values obtained for the control experiments performed on bare silicon.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 2

SEM image of type-B MWCNT (25μm in height) synthesized on silicon substrate: (a) side view before experiment, (b) top view before experiment, and (c) top view after experiment

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Figure 4

Saturated pool boiling curve for PF-5060 on type-B MWCNT forests (25μm in height) synthesized on silicon wafer. The saturation temperature of PF-5060=56°C. (a) Pool boiling curve for PF-5060 on type-B MWCNT. (b) Comparison of pool boiling curve for type-B MWCNT with bare silicon (the numbers in parenthesis denote the experimental run).

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Figure 5

Comparison of saturated pool boiling curve for PF-5060 on bare silicon and MWCNT synthesized on silicon. The MWCNT are of two different heights: type-A MWCNT (9μm in height) and type-B MWCNT (25μm in height). Saturation temperature of PF-5060=56°C (the numbers in parenthesis denote the experimental run).

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Figure 6

Images of boiling obtained during the experiments: (a) near CHF point on bare silicon wafer, (b) near Leidenfrost point on bare silicon wafer, (c) near CHF point on type-A MWCNT, (d) near Leidenfrost point on type-A MWCNT, (e) near CHF point on type-B MWCNT, and (f) near Leidenfrost point on type-B MWCNT

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Figure 1

Schematic diagram of experimental apparatus consisting of: (1) viewing chamber, (2) heater apparatus, and (3) silicon wafer surface with multiwalled carbon nanotube (MWCNT) forests

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Figure 3

Saturated pool boiling curve for PF-5060 on type-A MWCNT (9μm in height) synthesized on silicon wafer. Saturation temperature of PF-5060=56°C. (a) Pool boiling curve for PF-5060 on type-A MWCNT. (b) Comparison of pool boiling curve of type-A MWCNT with bare silicon. (the numbers in parenthesis denote the experimental run.)

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