Summary on experimental methods for statistical transient analysis of two-phase gas-liquid flow. [BWR, PWR, and LMFBR] (original) (raw)
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Transient and statistical measurement techniques for two-phase flows: A critical review
International Journal of Multiphase Flow, 1976
Much work has been expended in the study of two-phase, gas-liquid flows. While it has been recognized superficially that such flows are not homogeneous in general, little attention has been paid to the inherent discreteness of the two-phase systems. It has been a relatively recent development that fluctuating characteristics of two-phase flows have been studied in detail. As a result, new experimental devices and techniques have been developed for use in obtaining measurements of quantities previously ignored. This paper reviews and summarizes these methods in an effort to emphasize the importance of the fluctuating nature of these flows and as a guide to further research in this field.
2016
Abstract: Gas assisted atomization is becoming increasingly important in many industrial applications such as physical, chemical and petroleum processes. In order to achieve proper atomization it is crucial to have proper mixing of gas (air) and liquid (water) in the feeding conduit before it enters into the nozzle. The flow regime, as well as the flow pattern and structure of the flow, are some of the important parameters that describe two-phase gas/liquid flows, and identify two-phase gas/liquid flow regimes. It is also desirable to know under what conditions there is a transition among the different flow regimes (dispersed, stratified, annular, annular-dispersed, slug, wavy-slug, mist-annular). Due to the existence of relative movement in the interfaces and variable interactions between two phases, two-phase gas/liquid flow is a complex transport phenomenon compared to single-phase flow. Still, there is no effective technique to identify the two-phase gas/liquid flow regimes and ...
Mechanical Engineering Journal, 2015
A subchannel void sensor (SCVS) was developed to measure the cross-sectional distribution of void fraction in a 5×5 heated rod bundle with o.d. 10 mm and heated length 2000 mm, and applied to a boiling two-phase flow experiment under the atmospheric pressure condition assuming at an accident or in a spent fuel pool in a boiling water reactor (BWR). The SCVS comprises 6-wire by 6-wire and 5-rod by 5-rod electrodes. The wire electrodes of 0.2 mm in diameter are arranged in lattice patterns between the rod bundle, while the electric conductance value in a region near one wire and another corresponds to local void fraction in the central-subchannel region. The local void fractions at 32 points (= 6×6-4) can be obtained as a cross-sectional distribution. The local void fractions near the rod surface at 100 points (= 4×25) can be also estimated by the conductance value in a region between one wire and one rod. The devised sensors are installed at five height levels along the axis to acquire two-phase flow behavior. A pair of SCVS is mounted at each level and placed 30 mm apart to estimate the one-dimensional phasic velocity distribution based on the cross-correlation analysis of both layers. The temporal resolution of void fraction measurement is 1600 frames (cross-sections) per second. The axial and radial power profile of the heated rod bundle are uniform, and eight pairs of sheath thermocouples are embedded on the heated rod to monitor its surface temperature distribution. The boiling two-phase flow experiment, which simulated a boil-off process, was conducted with the devised SCVS and experimental data was acquired under various inlet flow velocity, rod bundle power and inlet subcooling conditions. The experimental results were presented by the axial and cross-sectional distributions of void fraction, phasic velocity and bubble-chord length.
A Critical Review of Advanced Experimental Techniques to Measure Two-Phase Gas/Liquid Flow
The Open Fuels & Energy Science Journal, 2009
Gas assisted atomization is becoming increasingly important in many industrial applications such as physical, chemical and petroleum processes. In order to achieve proper atomization it is crucial to have proper mixing of gas (air) and liquid (water) in the feeding conduit before it enters into the nozzle. The flow regime, as well as the flow pattern and structure of the flow, are some of the important parameters that describe two-phase gas/liquid flows, and identify twophase gas/liquid flow regimes. It is also desirable to know under what conditions there is a transition among the different flow regimes (dispersed, stratified, annular, annular-dispersed, slug, wavy-slug, mist-annular). Due to the existence of relative movement in the interfaces and variable interactions between two phases, two-phase gas/liquid flow is a complex transport phenomenon compared to single-phase flow. Still, there is no effective technique to identify the two-phase gas/liquid flow regimes and it is even difficult to capture the accurate flow structures in smaller conduits in turbulent flow cases. Lack of solid and comprehensive theories for predicting and calculating the pressure and void fraction variations in two-phase air/water flow situations has left engineers without essential information for proper design of two-phase flow systems. This review is an effort to explore the state of the present advanced measurement techniques in this field of research. Subsequently, some of the advanced void fraction, photonics and pressure measurement techniques and correlations for identification of two-phase gas/liquid flow regimes and bubble sizes are investigated.
Measurement and Modeling of Flow Pattern Transitions in Gas-Liquid Systems
Multiphase Science and Technology, 2017
This paper gives a comprehensive interpretation on the flow patterns occurring in gas-liquid horizontal, inclined and vertical pipeline flows and investigates various effects on their transitions. The postulated theoretical models for prediction of flow pattern transitions in systems without mass transfer are presented in detail. For horizontal pipe flows with boiling and condensation, a modified mechanistic theory is suggested� the predicted transitions are in good agreement with the experimental data. Finally, the approaches developed by Venkateswarar et al. (1982) to modelling the flow pattern transition for two-phase flows of steam and water in vertical rod bundles are presented.
Experimental study of the two-phase flow dynamics in nucleate and film pool boiling
International Journal of Multiphase Flow, 1996
An experimental study is conducted to measure the transient characteristics of the local boiling process close to the heated wall. Nucleate and film boiling two-phase parameters were measured for power oscillations in a small horizontal heater immersed in stagnant liquid. A method for measuring fast temporal variations of void fraction and the interfacial impact rate is presented. Ensemble averages of the data have been carried out to obtain time evolution of the void fraction and the interfacial impact rate at the probe tip. R-II3, R-II and water have been used as working fluids, finding important differences between the behavior of the freons and water at the boiling crises. The critical heat flux in freons is associated with a sudden transition in the impact rate and the void fraction, which supports the theory of hydrodynamic instability. On the other hand, the experiments in water suggest the existence of two transitions: a hydrodynamic transition from bubbling regime to "mushroom" regime followed by a liquid film dryout type of CHF, in agreement with the theory of Haramura & Katto.
Nuclear Engineering and Design, 2010
As a series of subcooling boiling flow tests, local two-phase flow parameters were obtained at SUBO (subcooled boiling) test facility under steam-water flow conditions. The test section is a vertical annulus of which the axial length is 4.165 m with a heater rod at the center of a channel. The inner and outer diameters of the test section and the heater rod are 35.5 mm and 9.98 mm, respectively. The test was performed by a two-stage approach. Stage-I for the measurement of local bubble parameters has been already done . The present work focused on the stage-II test for the measurement of local liquid parameters such as a local liquid velocity and a liquid temperature for a given flow condition of stage-I. A total of six test cases were chosen by following the test matrix of stage-I. The flow conditions are in the range of the heat flux of 370-563 kW/m 2 , mass flux of 1110-2100 kg/(m 2 s) and inlet subcooling of 19-31 • C at pressure condition of 0.15-0.2 MPa. From the test, local liquid parameters were measured at 6 elevations along the test section and 11 radial locations of each elevation in addition to the previously obtained local void fraction, interfacial area concentration, Sauter mean diameter and bubble velocity. The present subcooled boiling (SUBO) data completes a data set for use as a benchmark, validation and model development of the Computational Fluid Dynamics (CFD) codes or existing safety analysis codes.
Nuclear Engineering and Design, 2016
Multi-phase flows are one of the challenges on which the CFD simulation community has been working extensively with a relatively low success. The phenomena associated behind the momentum and heat transfer mechanisms associated to multi-phase flows are highly complex requiring resolving simultaneously for multiple scales on time and space. Part of the reasons behind the low predictive capability of CFD when studying multi-phase flows, is the scarcity of CFD-grade experimental data for validation. The complexity of the phenomena and its sensitivity to small sources of perturbations makes its measurements a difficult task. Non-intrusive and innovative measuring techniques are required to accurately measure multi-phase flow parameters while at the same time satisfying the high resolution required to validate CFD simulations. In this context, this work explores the feasible implementation of innovative measuring techniques that can provide whole-field and multi-scale measurements of two-phase flow turbulence, heat transfer, and boiling parameters. To this end, three visualization techniques are simultaneously implemented to study subcooled boiling flow through a vertical rectangular channel with a single heated wall. These techniques are listed next and are used as follow: 1) High-speed infrared thermometry (IR-T) is used to study the impact of the boiling level on the heat transfer coefficients at the heated wall, 2) Particle Tracking Velocimetry (PTV) is used to analyze the influence that boiling parameters have on the liquid phase turbulence statistics, 3) Highspeed shadowgraphy with LED illumination is used to obtain the gas phase dynamics. To account for the accuracy and to complement these innovative techniques, redundant and simultaneous measurements are performed by means of thermocouples, flow and power meters, differential and absolute pressure transducers, etc. The present experiments are intended to improve the understanding of subcooled boiling flow and to provide reliable and accurate subcooled boiling flow experimental information for verification and validation of two-phase flow computational models.