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Research Papers

Bubbles Transient Growth in Saturation Boiling of PF-5060 Dielectric Liquid on Dimpled Cu Surfaces

[+] Author and Article Information
Arthur Suszko

Institute for Space and Nuclear Power Studies,
University of New Mexico,
Albuquerque, NM 87131;
Mechanical Engineering Department,
University of New Mexico,
Albuquerque, NM 87131

Mohamed S. El-Genk

Institute for Space and Nuclear Power Studies,
University of New Mexico,
Albuquerque, NM 87131;
Nuclear Engineering Department,
University of New Mexico,
Albuquerque, NM 87131;
Mechanical Engineering Department,
University of New Mexico,
Albuquerque, NM 87131;
Chemical and Biological Engineering Department,
University of New Mexico,
Albuquerque, NM 87131
e-mail: mgenk@unm.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received August 16, 2015; final manuscript received November 29, 2015; published online February 3, 2016. Assoc. Editor: Wei Li.

J. Thermal Sci. Eng. Appl 8(2), 021016 (Feb 03, 2016) (11 pages) Paper No: TSEA-15-1229; doi: 10.1115/1.4032367 History: Received August 16, 2015; Revised November 29, 2015

Investigated is the transient growth of vapor bubbles in saturation boiling of PF-5060 dielectric liquid on 10 × 10 mm, uniformly heated Cu surfaces with circular dimples, at an applied heat flux of 0.5 W/cm2. At such low heat flux, the surfaces are populated with growing discrete bubbles, emanating mostly from the manufactured dimples. The 300, 400, and 500 μm diameter and 200 μm deep dimples are manufactured in a triangular lattice with a pitch-to-diameter ratio of 2.0; thus, the total number of dimples increases with decreasing the dimple diameter. Captured video images of growing discrete bubbles at a speed of 210 frames per second (fps) confirm that the bubble diameter increases proportional to the square root of the growth time, and the bubble departure diameter and detachment frequency increase with increasing the dimple diameter. The total volumetric growth rate and diameter of the bubbles at departure increase with increasing the dimple diameter, ∼1.81, ∼4.75, and ∼8.2 mm3/s and ∼738 μm, ∼963 μm, and ∼1051 μm for the 300, 400, and 500 μm diameter dimples, respectively. The corresponding bubble detachment frequency is ∼8.6 Hz, ∼10.2 Hz, and ∼13.5 Hz, respectively. The fraction of the active dimples for bubble nucleation on the surfaces with 300, 400, and 500 μm dimples, at an applied heat flux of 0.5 W/cm2, is ∼0.85, ∼0.64, and ∼0.53, respectively. On these surfaces, the estimated bubble volume at departure is ∼0.21 mm3, ∼0.47 mm3, and ∼0.61 mm3, and the corresponding rate of energy removed by a single bubble is ∼1.99 mW, ∼5.24 mW, and ∼9.02 mW, respectively. These results help explain the measured enhancements in nucleate boiling and the critical heat flux (CHF) on the dimpled Cu surfaces.

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Figures

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Fig. 7

Estimates of the transient volumes of the growing bubble in saturation nucleate boiling of PF-5060 on dimpled Cu surfaces at an applied heat flux of 0.5 W/cm2

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Fig. 6

Sequential images of a growing single vapor bubble on the Cu surface with 300 μm diameter dimples

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Fig. 5

A captured sequence of images of transient bubble growth on the surface with 400 μm diameter dimples

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Fig. 4

A captured sequence of transient growth of single vapor bubble on the Cu surface with 500 μm dimples

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Fig. 3

Recorded photographs of growing bubbles in saturation nucleate boiling of PF-5060 dielectric liquid on uniformly heated dimpled Cu surfaces at applied heat fluxes ∼0.5–1.0 W/cm2: (a) Cu with 500 μm diameter dimples, (b) Cu with 400 μm diameter dimples, and (c) Cu with 300 μm diameter dimples

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Fig. 2

Enhancements of saturation nucleate boiling and CHF of PF-5060 dielectric liquid on dimpled surfaces

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Fig. 1

(a) Plane and (b) cross-sectional views of the assembled test section; and images of a dimpled Cu surface: (c) a section of a Cu surface with 500 μm diameter dimples, 50× and (d) test section with circular dimples

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Fig. 8

Comparison of the volumetric growth rates of vapor bubbles in saturation boiling of PF-5060 dielectric liquid on dimpled Cu surfaces

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Fig. 9

Transient growth of vapor bubbles in saturation boiling of PF-5060 liquid on dimpled Cu surfaces

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Fig. 11

Illustrations depicting nucleation and growth of vapor embryos on the inside surface of a dimple, then the coalescence into a large dimple bubble that emerges and continues to growth to eventual detachment, followed by a complete flooding of the dimple: (a) nucleating embryos, (b) growing embryos, (c) coalescing embryos, (d) dimple bubble, (e) growing bubble, (f) bubble necking, (g) detached bubble, and (h) nucleating embryo. These images are based on close examinations of the nucleate boiling process and transient bubble growth on the dimpled surfaces (Figs.36 and 10).

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Fig. 12

An Illustration of the growing bubble from a circular dimple

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Fig. 10

Images of growing vapor bubbles at dimple cavities in saturation nucleate boiling of PF-5060 on uniformly heated Cu surfaces with (a) 300 μm and (b) 500 μm diameter dimples, at a heat flux of 0.5 W/cm2

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