0
Research Papers: Evaporation, Boiling, and Condensation

On the Mechanism of Pool Boiling Critical Heat Flux Enhancement in Nanofluids

[+] Author and Article Information
Hyungdae Kim1

Department of Nuclear Engineering, Kyung Hee University, Yongin-city 446-701, Republic of Koreahdkims@khu.ac.kr

Ho Seon Ahn

Department of Mechanical Engineering, POSTECH, Pohang, Gyungbuk 790-784, Republic of Korea

Moo Hwan Kim

Department of Mechanical Engineering, POSTECH, Pohang, Gyungbuk 790-784, Republic of Koreamhkim@postech.ac.kr

The contact angle of the evaporating meniscus had a large scatter between advancing and receding contact angles due to the oscillating interface motion of the impinged droplet, as shown in Figs.  1315. In this study, the averaged values of the measured contact angles were used to estimate the surface tension force on the evaporating meniscus.

1

This author is currently working at Massachusetts Institute of Technology. This work was performed when he was working at POSTECH.

J. Heat Transfer 132(6), 061501 (Mar 25, 2010) (11 pages) doi:10.1115/1.4000746 History: Received April 07, 2009; Revised October 02, 2009; Published March 25, 2010; Online March 25, 2010

The pool boiling characteristics of water-based nanofluids with alumina and titania nanoparticles of 0.01vol% were investigated on a thermally heated disk heater at saturated temperature and atmospheric pressure. The results confirmed the findings of previous studies that nanofluids can significantly enhance the critical heat flux (CHF), resulting in a large increase in the wall superheat. It was found that some nanoparticles deposit on the heater surface during nucleate boiling, and the surface modification due to the deposition results in the same magnitude of CHF enhancement in pure water as for nanofluids. Subsequent to the boiling experiments, the interfacial properties of the heater surfaces were examined using dynamic wetting of an evaporating water droplet. As the surface temperature increased, the evaporating meniscus on the clean surface suddenly receded toward the liquid due to the evaporation recoil force on the liquid-vapor interface, but the nanoparticle-fouled surface exhibited stable wetting of the liquid meniscus even at a remarkably higher wall superheat. The heat flux gain attainable due to the improved wetting of the evaporating meniscus on the fouled surface showed good agreement with the CHF enhancement during nanofluid boiling. It is supposed that the nanoparticle layer increases the stability of the evaporating microlayer underneath a bubble growing on a heated surface and thus the irreversible growth of a hot/dry spot is inhibited even at a high wall superheat, resulting in the CHF enhancement observed when boiling nanofluids.

Copyright © 2010 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Figure 1

TEM photographs of nanoparticles dried after dispersion into pure water: (a) alumina and (b) titania

Grahic Jump Location
Figure 2

Schematic diagram of the pool boiling facility

Grahic Jump Location
Figure 3

Detailed design of the test heater

Grahic Jump Location
Figure 4

Visualization of boiling phenomena of pure water at q″∼1300 kW/m2 on the present flat surface heater with the thin disk fin to prevent the undesired bubble nucleation from the heater edge

Grahic Jump Location
Figure 5

Boiling curves for distilled water on a copper surface

Grahic Jump Location
Figure 6

Boiling curves for pure water and alumina nanofluid on a copper surface

Grahic Jump Location
Figure 7

Boiling curves for nanofluids: (a) alumina on copper, (b) titania on copper, (c) alumina on nickel, and (d) titania on nickel

Grahic Jump Location
Figure 8

SEM photographs of various copper heater surfaces: (a) fresh, (b) water-boiled, (c) alumina nanofluid-boiled, and (d) titania nanofluid-boiled

Grahic Jump Location
Figure 9

Boiling curves for preboiling of alumina nanofluids on a fresh copper surface and subsequent boiling of pure water on a nanofluid-boiled surface

Grahic Jump Location
Figure 10

Comparison of boiling curves for nanofluids on a fresh surface and pure water on a nanoparticle-fouled surface: (a) alumina on copper, (b) titania on copper, and (c) titania on nickel

Grahic Jump Location
Figure 11

Influence of the nanoparticle deposition in CHF increases in water-based alumina nanofluids. The average particle sizes were 47 nm in the present study and in Ref. 9, and 46 nm in Ref. 10. The filled and open symbols indicate the nanofluid tests on the fresh surfaces and the water tests on the alumina nanoparticle-fouled surface, respectively.

Grahic Jump Location
Figure 12

Static contact angles of a water droplet on (a) a water-boiled surface, (b) an alumina nanoparticle-fouled surface, and (c) a titania nanoparticle-fouled surface

Grahic Jump Location
Figure 13

Wetting of a water droplet on a water-boiled copper surface at 120°C, 140°C, and 160°C

Grahic Jump Location
Figure 14

Contact angle of a liquid meniscus evaporating on water-boiled surfaces: (a) copper and (b) nickel

Grahic Jump Location
Figure 15

Wetting of a water droplet on a titania nanoparticle-fouled copper surface at 140°C, 160°C, 180°C, and 200°C

Grahic Jump Location
Figure 16

Contact angle of a liquid meniscus evaporating on nanoparticle-fouled copper surfaces: (a) alumina and (b) titania

Grahic Jump Location
Figure 17

Comparison between the normalized vapor recoil force at various wall superheats and the surface tension force enhancement on clean and nanoparticle-fouled surfaces

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In