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Research Papers: Nuclear Power

Steady-State and Transient Behavior of Gas/Liquid Phase Boundaries in Impulse Pipes

[+] Author and Article Information
Rainer Hampel

University of Applied Sciences,
Zittau/Goerlitz,
Zittau, 02763 Germany

Contributed by the Nuclear Division of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received September 19, 2012; final manuscript received September 23, 2012; published online February 21, 2013. Editor: Dilip R. Ballal.

J. Eng. Gas Turbines Power 135(3), 032903 (Feb 21, 2013) (7 pages) Paper No: GTP-12-1367; doi: 10.1115/1.4007874 History: Received September 19, 2012; Revised September 23, 2012

For boiling water reactors (BWR) and steam generators, the water level is a safety-relevant process variable. The most commonly applied measuring method is based on the calculation of the liquid level from geodetic pressure differences to a reference column of defined height and density. However, transition processes occurring under operational and accident conditions may lead to dynamic changes in the reference level and, therefore, to fluctuations in the differential pressure signal. This paper presents experiments and numerical simulations on the steady-state and transient behavior of gas/liquid phase boundaries in “zero chamber level vessels” (ZCLV). In these slightly inclined miniature tubes, the constant reference level is provided by surface tension forces and the capillary effect, respectively. To investigate the basic topology of gas/liquid interfaces under simplified conditions (environmental parameters, no heat transfer), a test facility with optical access was developed. The construction allows for variations of the inner tube diameter, inclination angle, and liquid mass flow rate, respectively. By this means, experiments on phase boundaries were carried out for ethanol/air and water/air. The results provide information about the impact of geometry parameters and their interactions on the interface topology. In addition, the dynamic draining of excess liquid mass at the free end of the tube and at artificial weld seams, which is supposed to be the reason for temperature fluctuations observed in ZCLV during power operation of BWR, was experimentally analyzed. The measurements represent the basis for an experimental validation and optimizations of the numerical flow code ANSYS CFX 12.0. In the next step, water/vapor phase boundaries at 286 °C and 70 bars will be investigated by applying X-ray radiography to a scale model. The results will be discussed in context with the hydrostatic level measurement in BWR.

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Fig. 1

Hydrostatic level measurement in BWR with zero chamber level vessel (scheme)

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Fig. 2

Test facility for investigations on gas/liquid phase boundaries at ambient conditions (T = 25 °C, p = 1 atm)

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Fig. 3

Definition of the projected interface length, l, for all experimental investigations

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Fig. 4

Measured phase boundary lengths for ethanol/air, d = 7 mm, α = 2 deg

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Fig. 5

Measured phase boundary lengths for ethanol/air, d = 7 mm, α = 4 deg

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Fig. 6

Measured phase boundary lengths for ethanol/air, d = 9 mm, α = 2 deg

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Fig. 7

Measured phase boundary lengths for ethanol/air, d = 9 mm, α = 4 deg

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Fig. 8

Draining experiment for ethanol/air (d = 9 mm, α = 2 deg, m· = 4 ml/min, 1 mm weld) in time steps of 20 s

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Fig. 9

ANSYS CFX simulation of a draining experiment for ethanol/air (d = 9 mm, α = 2 deg, m· = 4 ml/min, 1 mm weld) for time steps of 10 s

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