[en] A multi-channel impedance void meter was developed to measure the mean value and fluctuating components of the area-averaged void fraction. The sensor was designed for vertical circular channel. The void meter was calibrated using void simulators and by measuring pressure drop along the channel. As an example of applications, the mean value and fluctuating components are measured for bubble and slug flow, and it is shown that the impedance void meter has good dynamic resolution which is required to investigate the propagation of void fraction waves

[en] Nonlinear void-signal is a measurement signal, which has the information of void fraction fluctuation in two-phase flow, such as impedance signal, conductivity signal and pressure fluctuation signal. And it used to analyze two-phase flow transients system like nuclear reactors under various accident conditions. These void-signals have much nonlinearity, so it has possibility of getting more information about two-phase flow transients system by analyzing nonlinearity of void-signal. For detecting and analyzing nonlinearities, bispectral analysis, which is based on the concepts of higher order spectra (HOS), is generally used. Bispectral analysis determines the degree of second-order phase coupling that exists between constituent frequencies of nonlinear signals. It can be viewed as a decomposition of the third moment (skewness) of a signal over frequency and proves useful for analyzing and characterizing the state of systems. In this paper, the nonlinear characteristics of void signal were investigated by using bispectral analysis

[en] An experimental study has been carried out for upward and downward two-phase flow to study local interfacial structures and interfacial area transport. The flow studied, is an adiabatic, air-water, co-current, two-phase flow, in 25.4 mm and 50.8 mm ID test sections. Flow regime map is obtained using the characteristic signals obtained from an impedance void meter, employing neural network based identification methodology. A four sensor conductivity probe is used to measure the local two phase flow parameters, in bubbly flow regime. The local profiles of these parameters as well as their axial development reveal the nature of the interfacial structures and the bubble interaction mechanisms occurring in the flow. Furthermore, this study provides a good database for the development of the interfacial area transport equation, which dynamically models the changes in the interfacial area along a flow field. An interfacial area transport equation is used for downward flow based on that developed for the upward flow, with certain modifications in the bubble interaction terms. The area averaged values of the interfacial area concentration are compared with those predicted by the interfacial area transport model. The differences in the interfacial structures and interfacial area transport in co-current downward and upward two-phase flows are studied

[en] The OECD/NRC PWR Subchannel and Bundle Tests (PSBT) benchmark was organized on the basis of NUPEC database. The purposes of the benchmark are the encouragement to develop a theoretically-base microscopic approach as well as the comparison of currently available computational approaches. The benchmark consists of two separate phases: void distribution benchmark and DNB benchmark. Subchannel-grade void distribution data was employed for validation of a subchannel analysis code under steady-state and transient conditions. DNB benchmark provided subchannel fluid temperature data which can be used to determine the turbulent mixing parameter for a subchannel code. The NUPEC PWR test facility consists of high pressure and high temperature recirculation loop, a cooling loop, and data recording system. The void fraction was measured by two different methods: A gamma-ray beam CT scanner system was used to determine the distribution of density/void fraction over the subchannel at steady-state flow and to define the subchannel averaged void fraction with an accuracy by ±3%. A multi-beam system was used to measure chordal averaged subchannel void fraction in rod bundle with accuracies of ±4% and ±5% for steady-state and transient, respectively. The purpose of this study is to provide analysis results for PSBT benchmark problems for void distribution, subchannel mixing, and DNB, as well as to evaluate the applicability of some mechanistic DNB models to PSBT benchmark data with the aid of subchannel analysis results calculated by the MATRA code

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[en] Short communication

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[en] A Real-Time Neutron Radiography (RTNR) system is developed to determine two-phase flow parameters for a vertical co-current two-phase flow channel with a hexagonal finned bundle. Image processing techniques are applied to visualize the two-phase flow, and procedures for measuring flow regime, cross-sectional averaged void fraction, time averaged void fraction, and void distribution for this complex geometry are discussed. The results show that the experimental flow regime map agrees well with an existing flow regime model for a hexagonal fined bundle. The hexagonal finned bundle is observed to significantly affect the void fraction, void migration, and void fluctuation along the axial flow channel

No abstract available

No abstract available