The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Takashi Hibiki - One of the best experts on this subject based on the ideXlab platform.
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Flow Regime Transition criteria for co current downward two phase Flow
Progress in Nuclear Energy, 2018Co-Authors: Manojkumar Lokanathan, Takashi HibikiAbstract:Abstract Downward two-phase Flow is observed in light water reactor accident scenarios such as loss of coolant accident (LOCA) and loss of heat sink accident (LOHS) due to loss of feed water or a secondary pipe break, and so, it is vital to have a thorough understanding of the Flow mechanisms and Regimes. With this point of view, Flow Regime Transition criteria for vertical downward Flow for a range of pipe diameters of 24–101.6 mm has been developed. Several models looked at the radial distribution of the bubbles and the wake effect of leading bubbles while others looked into the Kelvin-Helmholtz instability seen at the gas-liquid interface. The newly developed criteria have been compared to Flow Regime maps obtained via subjective and objective means, consisting of air-water data at atmospheric conditions as well as at an elevated pressure of 0.2 MPa. The new model is also compared to Flow Regime maps developed with different inlet conditions. Overall, the present model showed good agreements with the available data, with the exception of several 50.8 mm ID Flow Regime maps of different inlet conditions as well as a self-organizing neural network. This study also highlights the need for a more objective and consistent Flow Regime map data for large diameter pipes, the identification of cap-bubbly and churn-turbulent Flows in these maps, and the deviations observed between a supervised and self-organizing neural network (SONN).
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Axial development of gas-liquid Flow Regime maps in a vertical 5 × 5 rod bundle with prototypic spacer grids
Nuclear Engineering and Design, 2018Co-Authors: Hang Liu, Liang-ming Pan, Takashi Hibiki, Wenxiong Zhou, Quan-yao RenAbstract:Abstract In relation to the development of Flow Regime criteria for rod bundle geometry, this paper provides several experimental Flow Regime maps at different axial locations with simple and prototypic spacer grids, respectively. Experiments with vertical adiabatic air-water Flow were conducted under an atmospheric pressure condition. The experiment facility was composed of 5 × 5 rod arranged on a square pitch in a square casing with 9.5 mm outside diameter and 12.6 mm pitch. The inlet superficial gas velocities range from 0.01 to 8.69 m/s, while inlet superficial liquid velocities range from 0.06 to 2.51 m/s. New Flow Regime maps were acquired at three axial locations of z/DH = 21.9, 58.4 and 107 through high-speed camera images. The experimental maps obtained were compared with the existing analytical models of Flow Regime Transition criteria for vertical rod bundles. A reasonable agreement has been obtained between measured Flow Regime maps and models of the existing Flow Regime Transition criteria for rod bundles at fully developed Flow conditions. The different effects of two types of spacer grids on the Flow Regime Transition were also discussed in this paper.
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Experimental Study of Flow Regime Map in 5×5 Rod Bundle
Volume 6: Thermal-Hydraulics, 2017Co-Authors: Hang Liu, Liang-ming Pan, Quan-yao Ren, Takashi Hibiki, Wenxiong ZhouAbstract:In relation to development of the Flow Regime criteria for rod bundles, this paper provides an experimental Flow Regime map and compares the experimental map with the existing Flow Regime Transition criteria for vertical rod bundles so far. An experiment of vertical adiabatic air-water Flow was conducted under an atmosphere pressure conditions. The experiment facility was composed of 5×5 rod arranged on a square pitch in a square shell with 9.5 mm outside diameter and 12.6 mm pitch. A total of 242 data sets were acquired consisting of superficial gas Flow rates, 0.02–8.69 m/s, and superficial liquid Flow rates, 0.02–2.13 m/s. A new Flow Regime map was obtained and the Flow Regime Transition model for rod bundles was validated by the measured Flow Regime map. A fairly good agreement with some discrepancies has been obtained between the existing Flow Regime Transition criteria and measured Flow Regime maps for rod bundles.
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Flow Regime Transition criteria for upward two-phase Flow in vertical rod bundles
International Journal of Heat and Mass Transfer, 2017Co-Authors: Hang Liu, Takashi HibikiAbstract:Abstract The demand of accurate prediction for two-phase Flow behavior in a nuclear reactor core composed of fuel rod bundles or a heat exchanger composed of heat transfer tube bundles requires comprehensive understanding of Flow Regime, void fraction, heat transfer and pressure drop. In comparison with the great success in developing the two-phase Flow Regime Transition criteria for simple geometries such as pipes, annulus and rectangular channels, limited researches have been performed for developing the Flow Regime Transition criteria of upward two-phase Flow in vertical rod bundles. In the vertical rod bundles, slug bubbles spanning the bundle casing cannot exist due to their surface instability and the two-phase Flow characteristics in the vertical rod bundles are different from those in pipes, annulus or rectangular channels whose channel size are smaller than the length scale of the surface instability. This study has proposed a new Flow Regime Transition criteria model based on the analysis on the underlying physics of the upward two-phase Flow behavior in the vertical rod bundles. A reliable drift-flux correlation to predict void fraction in the vertical rod bundle developed recently has been used in modeling the Flow Regime Transition criteria. This study has classified the Flow Regime into 6 distinct Flow Regime such as bubbly, finely dispersed bubbly, cap-bubbly, cap-turbulent, churn and annular Flows. The newly developed Flow Regime Transition criteria have been compared with existing 4 Flow Regime maps obtained in vertical rod bundles. The fluid systems include air-water and steam-water. A fairly good agreement with some discrepancies has been obtained between the newly developed Transition criteria and the measured Flow Regime maps.
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Flow Regime Transition criteria for upward two-phase cross-Flow in horizontal tube bundles
Applied Thermal Engineering, 2017Co-Authors: Keyou Mao, Takashi HibikiAbstract:Abstract In comparison with great success in the two-phase Flow research for internal Flows, relatively limited two-phase researches have been performed for external Flows such as two-phase cross-Flow in horizontal tube bundles. The recent demand of compact and efficient design of shell-tube type heat exchangers requires comprehensive understanding of void fraction, heat transfer, pressure drop, Flow-induced vibration and Flow Regime in the shell side. The Flow Regimes are strongly related to the two-phase external-Flow structure and affect the heat transfer performance in the heat exchangers. To this end, extensive literature survey has been performed to understand the Flow Regime appearing in the upward two-phase cross-Flow in horizontal tube bundles. This study has classified the Flow Regime into 5 distinct Flow Regimes such as bubbly, cap bubbly, churn, finely dispersed bubbly and annular Flows. A new model of the Flow Regime Transition criteria has been proposed based on the analysis on the underlying physics of the upward two-phase cross-Flow behavior in horizontal tube bundles. The newly developed Flow Regime Transition criteria have been compared with 12 Flow Regime maps measured in horizontal tube bundles with normal square pitch array, normal triangular pitch array and parallel triangular pitch array. The test conditions of the 12 Flow Regime maps include the pitch/diameter ratio ranging from 1.17 to 1.5 and the tube diameter ranging from 0.00979 m to 0.020 m. The fluid systems are air-water, boiling iso-butane, boiling propane, boiling n-pentane, boiling R134a and R235fa. A fairly good agreement with some discrepancy has been obtained between the newly developed Transition criteria and the measured Flow Regime maps.
Tian Yao - One of the best experts on this subject based on the ideXlab platform.
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upstream Flow based mechanisms for global Flow Regime Transition of gas liquid two phase Flow in pipeline riser systems
Chemical Engineering Science, 2021Co-Authors: Suifeng Zou, Liejin Guo, Tian YaoAbstract:Abstract In order to develop the Transition models for undesirable two-phase Flow Regimes in a pipeline-riser system in offshore oil and gas production systems, the relation between the upstream Flow condition in the pipeline and the global Flow Regime is analysed. The Transition of local Flow pattern along the upstream pipeline, especially the slug dissipation behaviour, is found to be related to global Flow Regime Transition. The mechanisms for the Transition from stable Flow Regime to different undesirable Flow Regimes are proposed separately. A set of hybrid criteria is established and validated by experimental data. The proposed criteria can predict the Transition to undesirable conditions which are less severe but more common than the typical cases, compared with existing uniform criteria. The findings can help for better understanding of Flow Regime Transition in a pipeline-riser system with more complex layout of pipeline, and also the possible extension of laboratorial experimental results.
Betty Sovilla - One of the best experts on this subject based on the ideXlab platform.
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Cold-to-warm Flow Regime Transition in snow avalanches
The Cryosphere, 2018Co-Authors: Anselm Köhler, Jan-thomas Fischer, Riccardo Scandroglio, Mathias Bavay, Jim Mcelwaine, Betty SovillaAbstract:Abstract. Large avalanches usually encounter different snow conditions along their track. When they release as slab avalanches comprising cold snow, they can subsequently develop into powder snow avalanches entraining snow as they move down the mountain. Typically, this entrained snow will be cold ( T ‾ - 1 ∘ C) at high elevations near the surface, but warm ( T ‾ > - 1 ∘ C) at lower elevations or deeper in the snowpack. The intake of warm snow is believed to be of major importance to increase the temperature of the snow composition in the avalanche and eventually cause a Flow Regime Transition. Measurements of Flow Regime Transitions are performed at the Vallee de la Sionne avalanche test site in Switzerland using two different radar systems. The data are then combined with snow temperatures calculated with the snow cover model SNOWPACK. We define Transitions as complete when the deposit at runout is characterized only by warm snow or as partial if there is a warm Flow Regime, but the farthest deposit is characterized by cold snow. We introduce a Transition index Ft , based on the runout of cold and warm Flow Regimes, as a measure to quantify the Transition type. Finally, we parameterize the snow cover temperature along the avalanche track by the altitude Hs , which represents the point where the average temperature of the uppermost 0.5 m changes from cold to warm. We find that Ft is related to the snow cover properties, i.e. approximately proportional to Hs . Thus, the Flow Regime in the runout area and the type of Transition can be predicted by knowing the snow cover temperature distribution. We find that, if Hs is more than 500 m above the valley floor for the path geometry of Vallee de la Sionne, entrainment of warm surface snow leads to a complete Flow Regime Transition and the runout area is reached by only warm Flow Regimes. Such knowledge is of great importance since the impact pressure and the effectiveness of protection measures are greatly dependent on the Flow Regime.
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Cold-to-warm Flow Regime Transition in snow avalanches
2018Co-Authors: Anselm Köhler, Jan-thomas Fischer, Riccardo Scandroglio, Mathias Bavay, Jim Mcelwaine, Betty SovillaAbstract:Abstract. Large avalanches usually encounter different snow conditions along their track. When they release as slab avalanches comprising cold snow, they can subsequently develop into powder snow avalanches entraining snow as they move down the mountain. Typically, this entrained snow will be cold (T < −1 °C) at high elevations near the surface, but warm (T > −1 °C) at lower elevations or deeper in the snow pack. The intake of thermal energy in the form of warm snow is believed to cause a Flow Regime Transition. Measurements of Flow Regime Transitions are performed at the Vallée de la Sionne avalanche test site in Switzerland using two different radar systems. The data are then combined with snow temperatures calculated with the snow cover model SNOWPACK. We define Transitions as complete, when the deposit at runout is characterized only by warm snow, or as partial, if there is a warm Flow Regime but the furthest deposit is characterized by cold snow. We introduce a Transition factor Ft, based on the runout of cold and warm Flow Regimes, as a measure to quantify the Transition type. Finally, we parameterize the snow cover temperature along the avalanche track by the altitude Hs, which represents the point where the average temperature of the uppermost 0.5 m changes from cold to warm. We find that Ft is related to the snow cover properties, i.e. approximately proportional to Hs. Thus, the Flow Regime in the runout area and the type of Transition can be predicted by knowing the snow cover temperature distribution. We find, that, if Hs is more than 500 m above the valley floor for the path geometry of Vallée de la Sionne, entrainment of warm surface snow leads to a complete Flow Regime Transition and the runout area is reached by only warm Flow Regimes. Such knowledge is of great importance since the impact pressure and the effectiveness of protection measures are greatly dependent on the Flow Regime.
Suifeng Zou - One of the best experts on this subject based on the ideXlab platform.
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upstream Flow based mechanisms for global Flow Regime Transition of gas liquid two phase Flow in pipeline riser systems
Chemical Engineering Science, 2021Co-Authors: Suifeng Zou, Liejin Guo, Tian YaoAbstract:Abstract In order to develop the Transition models for undesirable two-phase Flow Regimes in a pipeline-riser system in offshore oil and gas production systems, the relation between the upstream Flow condition in the pipeline and the global Flow Regime is analysed. The Transition of local Flow pattern along the upstream pipeline, especially the slug dissipation behaviour, is found to be related to global Flow Regime Transition. The mechanisms for the Transition from stable Flow Regime to different undesirable Flow Regimes are proposed separately. A set of hybrid criteria is established and validated by experimental data. The proposed criteria can predict the Transition to undesirable conditions which are less severe but more common than the typical cases, compared with existing uniform criteria. The findings can help for better understanding of Flow Regime Transition in a pipeline-riser system with more complex layout of pipeline, and also the possible extension of laboratorial experimental results.
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Upstream-Flow-based Mechanisms for Global Flow Regime Transition of Gas/Liquid Two-phase Flow in Pipeline-riser Systems
Chemical Engineering Science, 2021Co-Authors: Suifeng Zou, Liejin Guo, Yao TianAbstract:Abstract In order to develop the Transition models for undesirable two-phase Flow Regimes in a pipeline-riser system in offshore oil and gas production systems, the relation between the upstream Flow condition in the pipeline and the global Flow Regime is analysed. The Transition of local Flow pattern along the upstream pipeline, especially the slug dissipation behaviour, is found to be related to global Flow Regime Transition. The mechanisms for the Transition from stable Flow Regime to different undesirable Flow Regimes are proposed separately. A set of hybrid criteria is established and validated by experimental data. The proposed criteria can predict the Transition to undesirable conditions which are less severe but more common than the typical cases, compared with existing uniform criteria. The findings can help for better understanding of Flow Regime Transition in a pipeline-riser system with more complex layout of pipeline, and also the possible extension of laboratorial experimental results.
Mamoru Ishii - One of the best experts on this subject based on the ideXlab platform.
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Experimental study of vertical co-current slug Flow in terms of Flow Regime Transition in relatively small diameter tubes
International Journal of Multiphase Flow, 2018Co-Authors: Muhao Zhang, Liang-ming Pan, Xiaohong Yang, Mamoru IshiiAbstract:Abstract In order to investigate the evolution characteristics of structure parameters during Flow Regime Transition process in gas-liquid slug Flow, the vertical upward slug Flow in a wide range of liquid superficial velocity (0.03
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Downward two phase Flow experiment and general Flow Regime Transition criteria for various pipe sizes
International Journal of Heat and Mass Transfer, 2018Co-Authors: Zijiang Yang, Mamoru Ishii, Xiaohong Yang, Zhuoran Dang, Jianqiang ShanAbstract:Abstract Flow Regime map is often used in choosing constitutive correlations for the two-phase Flow model. The related research mainly concentrates on the vertical upward and horizontal Flow, while it is not sufficient in the vertical downward Flow. Downward Flow is very important as it is frequently encountered in the industrial applications. To enrich the downward Flow research, an experiment is performed on a piping system with an inner diameter of 0.1524 m. Four different Flow patterns (bubbly Flow, cap bubbly Flow, churn turbulent Flow, and annular Flow) are classified with the artificial neural network method. The probability density function (PDF) profile of each Flow pattern is discussed. The proposed Flow Regime map is compared with the other experiments and the effect of the pipe size is discussed. The existing downward Flow Regime boundary criteria are assessed with the experiment results. It is found that these criteria cannot fit the experiment results well. A set of general boundary criteria are still needed. In this paper, the criteria for the boundary of the bubbly Flow, the boundary between the cap bubbly Flow and the slug Flow, and the boundary of the falling film Regime are proposed. They are verified with the experiments on different size pipes. A significant inlet effect on the Flow Regime boundary is found. The falling film boundary criterion proposed cannot be applied when a sparger is used to inject gas into the downward test section.
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Investigation of Slug Flow Structure in Terms of Flow Regime Transition in Co-Current Two-Phase Flow
Volume 9: Student Paper Competition, 2017Co-Authors: Muhao Zhang, Liang-ming Pan, Mamoru IshiiAbstract:In order to investigate the structure parameters evolution characteristics during Flow Regime Transition process in slug Flow, the vertical upward slug Flow experiment in a wide range of liquid superficial velocity (0.03 < jl < 1.6 m/s) were conducted in a tubular test section with the inside diameter of 25.4 mm. Impedance void meters were employed to measure the void fraction of separated two parts corresponding to Taylor bubble and liquid slug. The present research studied the evolution of length ratio and void fraction in slug unit by keeping the liquid superficial velocity constant while increasing gas Flow rate. New structure of slug unit in strong relation with Transition process was observed. In specific, it was realized that the proportion of such special structure unit played an important role in Transition from slug Flow to churn-turbulent Flow. The existing Transition criteria from slug Flow to churn-turbulent Flow in upward two-phase Flow (entrance effects model, flooding model, wake effects model, bubble coalescence model and Helmholtz instability model) were compared with the experimental identified results obtained by a new objective Flow Regime identification method, ReliefF-FCM algorithm. The results indicate that the Transition model based on the wake effects could be the most appropriate choice to describe the mechanism of Transition from slug Flow to churn-turbulent Flow in present experimental conditions.
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The mechanism of bubbly to slug Flow Regime Transition in air-water two phase Flow: A new Transition criterion
International Journal of Heat and Mass Transfer, 2017Co-Authors: Muhao Zhang, Liang-ming Pan, Xiaohong Yang, Mamoru IshiiAbstract:Abstract Air-water two-phase upward Flow experiments are conducted in a tubular test section with the inner diameter of 25.4 mm in order to investigate the Transition mechanism of bubbly Flow to slug Flow. Flow Regime identification is carried out by using ReliefF-FCM clustering algorithm, i.e., a new objective Flow Regime identification method. It is found that the velocity ratio decreases with the increase of superficial gas velocity in bubbly Flow at the constant liquid superficial velocity. And the velocity ratio always reaches its minimum during the Flow Regime Transition. The present research finds that the changes of bubble size and shape may result in the decrease of velocity ratio in bubbly Flow. From this point of view, a new mechanism for bubbly to slug Flow Regime Transition has been proposed. A Transition criterion based on the mechanism is also built. The comparison of the Transition criterion with the experimental results at different Flow conditions is carried out. Although the Transition criterion is empirically modified based on the present experimental data, it shows the reasonable agreements.