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RESEARCH PAPERS

A Transient Nucleate Boiling Model Including Microscale Effects and Wall Heat Transfer

[+] Author and Article Information
Thomas Fuchs, Jürgen Kern

Chair of Technical Thermodynamics, Darmstadt University of Technology, Petersenstrasse 30, 64287 Darmstadt, Germany

Peter Stephan

Chair of Technical Thermodynamics, Darmstadt University of Technology, Petersenstrasse 30, 64287 Darmstadt, Germanypstephan@ttd.tu-darmstadt.de

J. Heat Transfer 128(12), 1257-1265 (Apr 05, 2006) (9 pages) doi:10.1115/1.2349502 History: Received July 27, 2005; Revised April 05, 2006

A new model is presented to compute nucleate boiling heat and mass transfer. It is based on a previous one (Kern, J., and Stephan, P., 2003, ASME J. Heat Transfer, 125, pp. 1106–1115) for quasi-stationary heat transfer to single vapor bubbles. In contrast to the preceding model, fully transient heat and fluid flow is computed with a free surface of the rising bubble and a periodic calculation of repeated cycles of bubble growth, detachment, and rise, requiring only specification of the waiting time between successive bubbles. Additionally, microscopic effects at the foot of the bubble are considered. The model is verified by comparing computed with measured heat transfer coefficients. Typical results for heat and mass transfer to a single vapor bubble are shown at all time steps of the bubble cycle. By means of the model the transient heat flow through different interfaces, e.g., wall/liquid or liquid/vapor, is computed for the whole bubble cycle. Thus, it was possible to evaluate the influence of transient heat conduction, heat storage, and convection in liquid as well as heat transfer in the wall on overall heat transfer performance.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Subsystem and computational domains

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Figure 2

Significant phenomena in the micro region

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Figure 3

Definition of phases for the initial bubble cycle and subsequent bubble cycles

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Figure 4

Finite element grid (a), streamlines (b), and isobars (c) at different stages of the bubble cycle (propane/n-butane, p*=0.2, Tout−Tsat=8.7K, xL,1=0.245, dsub=0.4mm)

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Figure 5

(a) and (b) Isotherms (ΔTiso,w=5*10−4K, ΔTiso,l=0.17K), (c) magnification of isotherms near the micro region (ΔTiso,w=5*10−4K, ΔTiso,l=0.17K)

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Figure 6

Definition of interfaces of the subsystem

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Figure 7

Time-dependent heat flow through interface 1 (propane/n-butane, p*=0.2, Tout−Tsat=8.7K, xL,1=0.245, dsub=0.4mm)

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Figure 8

Time-dependent heat flow through interfaces 2, 3, and 5 (propane/n-butane, p*=0.2, Tout−Tsat=8.7K, xL,1=0.245, dsub=0.4mm)

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Figure 9

Time-dependent heat flow through interfaces 1–3 as well as heat storage in the wall (propane/n-butane, p*=0.2, Tout−Tsat=8.7K, xL,1=0.245, dsub=0.4mm)

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Figure 10

Time-dependent heat flow through interfaces 2 and 5 or 6 as well as heat storage in the liquid (propane/n-butane, p*=0.2, Tout−Tsat=8.7K, xL,1=0.245, dsub=0.4mm)

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