Experimental and numerical investigation of sub-cooled boiling, condensation, and void flashing in nuclear heating reactor test loop

X. Yang; S. Y. Jiang; Y. Zhang

doi:10.1515/kern-2002-0041

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Experimental and numerical investigation of sub-cooled boiling, condensation, and void flashing in nuclear heating reactor test loop

X. Yang , S. Y. Jiang and Y. Zhang

Published/Copyright: March 17, 2022

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From the journal Kerntechnik Volume 67 Issue 2-3

Abstract

This paper describes experimental and numerical investigations of sub-cooled boiling, condensation, and void flashing in the HRTL-5 test loop, which simulates the primary loop of a 5 MW nuclear heating reactor. A drift-flow model of two-phase with four governing equations was used, in which sub-cooled boiling, condensation, and void flashing have been taken into account. Based on the mathematical model, a program has been developed for analyzing the natural circulation system. As parameters, inlet sub-cooling, system pressure, and heat flux are varied. For comparison, some simplified models, which are designed to reveal the importance of sub-cooled boiling, condensation, flashing in the HRTL-5 test loop, are adopted in the program. The results show: (1) sub-cooled boiling, condensation, and void flashing may have great influence on the distribution of the void fraction and more intense at low system pressure; (2) the calculation of them is correlative and interactive other than independent; (3) for a system with short heated section, long riser, and low pressure, it is possible to reach “boiling out of the core”, where there is almost no void in the heated section, but much in the riser.

Abstract

Diese Arbeit beschreibt experimentelle und numerische Untersuchungen von unterkühltem Sieden, Kondensation und Blasenverdampfung in der Testschleife HRTL-5, die die Primärschleife eines 5 MW nuklearen Heizreaktors simuliert. Ein zwei-Phasen Drift-Flow Modell mit vier Haupt-Gleichungen wurde verwendet, das unterkühltes Sieden, Kondensation und Blasenverdampfung berücksichtigt. Auf der Grundlage des mathematischen Modells wurde ein Computer-Code zur Analyse des Systems mit Naturumlauf entwickelt. Als Parameter wurden Eintrittsunterkühlung, Systemdruck und Wärmefluss variiert. Zum Vergleich wurden einige vereinfachte Modelle, die darauf ausgelegt sind, die Bedeutung von unterkühltem Sieden, Kondensation und Blasenverdampfung zu beschreiben, an das Computerprogramm angepasst. Die Ergebnisse zeigen: (1) unterkühltes Sieden, Kondensation und Blasenverdampfung können einen großen Einfluss auf die Verteilung des Dampfblasenanteils haben und dies umso mehr bei niedrigem Systemdruck; (2) ihre Berechnung ist eher korrelativ und interaktiv als unabhängig voneinander; (3) für ein System mit kurzem Heizbereich, langem Steigrohr und niedrigem Druck ist es möglich „ein Sieden aus dem Kern heraus“ zu erreichen, wobei sich fast keine Dampfblasen im Heizbereich befinden aber umso mehr im Steigrohr.

References

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This work has been supported as Project 1987 2040 by the National Natural Science Foundation of China.

List of symbols

A: flow area
C₀: distribution parameter in Drift-Model
c_p: specific heat capacity at const pressure
g: acceleration of gravity
h: specific enthalpy
p: pressure
q: heat flux
Qc: heat condensed from sub-cooled vapor to water
r: latent heat
R_b: radius of sub-cooled steam bubble
t: time
T: temperature
ΔT: inlet sub-cooling
U: perimeter of heated rods
V_dj: relative velocity in Drift-Model
z: running distance above inlet of heated section
ψ: fraction of heat-generated vapor at surface of heated rod
ρ: density
ω: velocity
ε: void fraction
τ: rate of vapor generated

Subscripts

D: vapor
f: resistance
F: water or flashing front
FD: difference between vapor and water properties
FDB: bubble departing point
g: gravity
H: exit position of heated section
K: riser
l: local
m: mixing
ONB: boiling beginning point
s: saturated condition
S: bulk boiling front
w: wall of heated rods

Received: 2002-02-25

Published Online: 2022-03-17

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https://doi.org/10.1515/kern-2002-0041