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Research Papers

High-Resolution Measurements at Nucleate Boiling of Pure FC-84 and FC-3284 and Its Binary Mixtures

[+] Author and Article Information
Enno Wagner

 Weingartenstrasse 33, D-64367 Mühltal, Germanyenno.wagner@gmx.de

Peter Stephan1

Department of Mechanical Engineering, Institute of Technical Thermodynamics, Technische Universität Darmstadt, D-64287 Darmstadt, Germanypstephan@ttd.tu-darmstadt.de

DKD: German Calibration Service.

The data were recorded within the scope of a cooperative DFG boiling project at the RWTH Aachen, Chair of Thermal Process Engineering.

1

Corresponding author.

J. Heat Transfer 131(12), 121008 (Oct 15, 2009) (12 pages) doi:10.1115/1.3220143 History: Received February 15, 2008; Revised January 12, 2009; Published October 15, 2009

In a special boiling cell, vapor bubbles are generated at single nucleation sites on top of a 20μm thick stainless steel heating foil. An infrared camera captures the rear side of the heating foil for analyzing the temperature distribution. The bubble shape is recorded through side windows with a high-speed camera. Global measurements were conducted, with the pure fluids FC-84 and FC-3284 and with its binary mixtures of 0.25, 0.5, and 0.75mole fraction. The heat transfer coefficient (HTC) in a binary mixture is less than the HTC in either of the single component fluid alone. Applying the correlation of Schlünder showed good agreement with the measurements (1982, “Über den Wärmeübergang bei der Blasenverdampfung von Gemischen  ,” Verfahrenstechnik, 16(9), pp. 692–698). Furthermore, local measurements were arranged with high lateral and temporal resolution for single bubble events. The wall heat flux was computed and analyzed, especially at the three-phase-contact line between liquid, vapor, and heated wall. The bubble volume and the vapor production rate were also investigated. For pure fluids, up to 50–60% of the latent heat flows through the three-phase-contact region. For mixtures, this ratio is clearly reduced and is about 35%.

Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Design of the boiling cell with an electric foil heater

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Figure 2

Energy balance of one single pixel element

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Figure 3

HTCs for FC-84, measurements, and calculations

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Figure 4

Boiling and condensation curves of FC-84/FC-3284 binary mixtures at 500mbar and 950mbar absolute pressures

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Figure 5

Boiling curves for FC-84 and FC-3284 and a binary mixture with x=0.5, all at 500mbar system pressure

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Figure 6

Graph of heat transfer coefficients for FC-84 and FC-3284 and binary mixtures with x=0.25, x=0.5, and x=0.75, all at 500mbar system pressure

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Figure 7

Graph of heat transfer coefficients for FC-84 and FC-3284 and binary mixtures with x=0.25, x=0.5, and x=0.75, all at 950mbar system pressure

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Figure 8

HTCs as a function of the mole fraction x of the more volatile component FC-3284

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Figure 9

Bubble shape, IR temperature field (°C), temperature line profile, and heat flux distribution (W∕m2) at τ=56ms

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Figure 10

Bubble shape, IR temperature field (°C), temperature line profile, and heat flux distribution (W∕m2) at τ=58ms

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Figure 11

Bubble shape, IR temperature field (°C), temperature line profile, and heat flux distribution (W∕m2) at τ=60ms

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Figure 12

Bubble shape, IR temperature field (°C), temperature line profile, and heat flux distribution (W∕m2) at τ=62ms

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Figure 13

Bubble shape, IR temperature field (°C), temperature line profile, and heat flux distribution (W∕m2) at τ=64ms

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Figure 14

Bubble shape, IR temperature field (°C), temperature line profile, and heat flux distribution (W∕m2) at τ=66ms

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Figure 15

Bubble shape, IR temperature field (°C), temperature line profile, and heat flux distribution (W∕m2) at τ=68ms

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Figure 16

Bubble shape, IR temperature field (°C), temperature line profile, and heat flux distribution (W∕m2) at τ=70ms

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Figure 17

Measurement results of single bubble test series with FC-84, FC-3284, and a 0.5M binary mixture at 500mbars. Top: bubble departure diameter; center: bubble frequency; bottom: wall superheat; all as a function of heat flux.

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Figure 18

Time progression of measured bubble volume (Vbub,meas), fitted polynominal (Vbub,poly), latent heat flux (Q̇bub), microregion heat flux (Q̇mic), and ration of microregion heat flux (Q̇mic∕Q̇bub) during bubble growth. Top: FC-84 at 12,000W∕m2; center: FC-3284 at 12,900W∕m2; bottom: FC-mix, x=0.5 at 14,400W∕m2.

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