Flow Pattern Transition Criteria for Upward Two-Phase Flow in Annulus

2020 ◽  
Author(s):  
He Wen ◽  
Zhao Chenru ◽  
Bo Hanliang
Keyword(s):  
Flow Pattern ◽  
Flow Patterns ◽  
Flow Transition ◽  
Two Phase ◽  
Transition Mechanism ◽  
Flow Pattern Transition ◽  
Transition Criteria ◽  
Asymmetric Shape ◽  
Basic Characteristics ◽  
Churn Flow

Abstract Vertical upward two-phase flows in annulus are of great importance in many industrial fields due to the closely relationship between the flow patterns and the heat transfer characteristics. Common flow patterns in annulus are bubbly (B), slug (S), churn (C) and annular (A) flow, most of which are quite similar to those in tubes. However, due to the elliptic nose and asymmetric shape of the Taylor bubble in annulus, the slug to churn flow transition could be influenced by the channel geometry which was usually ignored in most of the previous researches. The flow pattern transition criteria for tubes are thus not applicable for annulus, especially for slug to churn flow transition, which should be separately studied. Therefore, in this paper, the basic characteristics of the flow pattern in annulus and their transition mechanism are analyzed. In addition, a set of semi-empirical transition criteria with higher accuracy are assessed and selected for annulus based on theoretical analysis and comparisons with experimental data.

Detecting the Flow Pattern Transition in the Gas-Liquid Two-Phase Flow Using Multivariate Multi-Scale Entropy Analysis

2019 ◽  
Vol 74 (10) ◽  
pp. 837-848 ◽  
Author(s):  
Yudong Liu ◽  
Dayang Wang ◽  
Yingyu Ren ◽  
Ningde Jin
Keyword(s):  
Flow Pattern ◽  
Two Phase Flow ◽  
Flow Patterns ◽  
Mean Value ◽  
Entropy Rate ◽  
Permutation Entropy ◽  
Phase Flow ◽  
Two Phase ◽  
Multi Scale ◽  
Flow Pattern Transition

AbstractDue to the complex flow structure and non-uniform phase distribution in the vertical upward gas-liquid two-phase flow, an eight-electrode rotating electric field conductance sensor is used to obtain multi-channel conductance signals. The flow patterns of the vertical upward gas-liquid two-phase flow are classified according to the images obtained from a high-speed camera. Then, we employ the multivariate weighted multi-scale permutation entropy (MWMPE) to detect the instability of flow pattern transition in the gas-liquid two-phase flow. Afterwards, we compare the results of the MWMPE with those of the single-channel weighted multi-scale permutation entropy (SCWMPE) and multivariate multi-scale sample entropy (MMSE). The comparison results indicate that, compared with the SCWMPE and MMSE, the MWMPE has superior performance in terms of the high-resolution presentation of flow instability in the gas-liquid two-phase flow. Finally, we extract the mean value of the MWMPE in whole scales and the entropy rate of the MWMPE in the small scales. The results indicate that the normalized mean value and normalized entropy rate of MWMPE are very sensitive to the transitions of flow patterns, thus allowing the detection of the instability of flow pattern transition.

An Experimental Study on Air-Water Two-Phase Flow Patterns in Pebble Beds

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Bai Bofeng ◽  
Liu Maolong ◽  
Su Wang ◽  
Zhang Xiaojie
Keyword(s):  
Experimental Study ◽  
Flow Pattern ◽  
Test Section ◽  
Slug Flow ◽  
Annular Flow ◽  
Two Phase Flow ◽  
Flow Patterns ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Pattern Transition

An experimental study was conducted on the air-water two-phase flow patterns in the bed of rectangular cross sections containing spheres of regular distribution. Three kinds of glass spheres with different diameters (3 mm, 6 mm, and 8 mm) were used for the establishment of the test section. By means of visual observations of the two-phase flow through the test section, it was discovered that five different flow patterns occurred within the experimental parameter ranges, namely, bubbly flow, bubbly-slug flow, slug flow, slug-annular flow, and annular flow. A correlation for the bubble and slug diameter in the packed beds was proposed, which was an extended expression of the Tung/Dhir model, Jamialahmadi’s model, and Schmidt’s model. Three correlations were proposed to calculate the void friction of the flow pattern transition in bubble flow, slug flow, and annular flow based on the bubble model in the pore region. The experimental result showed that the modified Tung and Dhir model of the flow pattern transition was in better agreement with the experimental data compared with Tung and Dhir’s model.

Simulation on Flow Pattern Transition With Liquid Nitrogen and its Vapor Using a Droplet Entrainment Model

2020 ◽  
Author(s):  
Rui Zhou ◽  
Tao Xia ◽  
Xiaobin Zhang
Keyword(s):  
Flow Pattern ◽  
Liquid Nitrogen ◽  
Slug Flow ◽  
Flow Patterns ◽  
Eulerian Model ◽  
Ansys Fluent ◽  
Droplet Entrainment ◽  
Flow Pattern Transition ◽  
Churn Flow ◽  
Two Fluid

Abstract A droplet entrainment model was applied to characterize the flow pattern transition in the countercurrent horizontal flow with liquid nitrogen (LN2) and vapor nitrogen (VN2). A two-fluid three-field model consisting of liquid film, gas, and droplet was implemented based on the Eulerian-Eulerian model in ANSYS Fluent®. In the droplet entrainment model, the condition and position of the droplet generation were realized by calculating the velocity gradient in the normal direction of the interface towards the gas core. The droplet entrainment and deposition rates were also included and validated according to the available data of water/air in the literature. Three flow patterns, including stratified-wavy flow, churn flow, and pseudo-slug flow, were identified in simulation results with LN2/VN2. Furthermore, ligament breakup was found to be the main droplet entrainment mechanism in the churn and pseudo-slug flow, and there can be a high probability of the occurrence of bubble burst as well. Compared with water/air, the droplets are more easily to be entrained in LN2/VN2 due to the smaller viscosity and surface tension according to the results of droplet mass flow rate. Pressure drop signals of the three flow patterns were also obtained and analyzed.

Photographic Study on Two-Phase Flow Patterns of Water in a Single-Side Heated Narrow Rectangular Channel

2010 ◽  
Author(s):  
Jun-Feng Wang ◽  
Yan-Ping Huang ◽  
Yan-Lin Wang
Keyword(s):  
Two Phase Flow ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Flow Patterns ◽  
Two Dimensions ◽  
Phase Flow ◽  
Two Phase ◽  
Single Side ◽  
Transition Criteria ◽  
Churn Flow

Visualized experimental observation on flow patterns during flow boiling of water under single-side heated and fluid-inlet subcooled conditions in a vertical narrow rectangular channel with the cross-section of 40×3mm2 have been carried out. Four discernible flow patterns which names dispersed bubbly, coalesced bubbly, churn flow and annular flow are obtained. Flow visualization in two dimensions of two-phase flow patterns for narrow rectangular channel, which provided clearer evidence to distinguish flow patterns, have been performed. Based on the experimental results, a flow pattern map for single-side heated narrow rectangular channel has been developed and then compared with the exiting maps and flow transition criteria.

Photographic Study on Two-Phase Flow Patterns of Water in a Single-Side Heated Narrow Rectangular Channel

2010 ◽  
Vol 133 (5) ◽  
Author(s):  
Junfeng Wang ◽  
Yanping Huang ◽  
Yanlin Wang
Keyword(s):  
Two Phase Flow ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Flow Patterns ◽  
Two Dimensions ◽  
Phase Flow ◽  
Two Phase ◽  
Single Side ◽  
Transition Criteria ◽  
Churn Flow

Visualized experimental observation on flow patterns during flow boiling of water under single-side heated and fluid-inlet subcooled conditions in a vertical narrow rectangular channel with the cross section of 40×3 mm2 have been carried out. Four discernible flow patterns, which names dispersed bubbly, coalesced bubbly, churn flow, and annular flow are observed. Flow visualization in two dimensions of two-phase flow patterns for narrow rectangular channel, which provided clearer evidence to distinguish flow patterns, have been performed. Based on the experimental results, a flow pattern map for single-side heated narrow rectangular channel has been developed and then compared with the exiting maps and flow transition criteria.

Investigation on Flow Patterns and Transition Characteristics in a Tube-Bundle Channel

2009 ◽  
Author(s):  
Guangyao Lu ◽  
Guisheng Zhao ◽  
Junsheng Ren ◽  
Wenyuan Xiang ◽  
Huaning Ai
Keyword(s):  
Flow Pattern ◽  
High Speed ◽  
Tube Bundle ◽  
Bubbly Flow ◽  
Flow Patterns ◽  
Vertical Tube ◽  
Two Phase ◽  
Flow Pattern Map ◽  
Boiling Flow ◽  
Churn Flow

Tube-bundle channels have been widely used in condenser-evaporator and other industrial heat-exchange equipments. The characteristics of two-phase flow patterns and their transitions for refrigerant R-113 through a vertical tube-bundle channel are experimentally investigated using high-speed camera. Experiments show that there are four main flow patterns in the tube-bundle channel, which are bubbly flow, bubbly-churn flow, churn flow and annular flow. And in the same cross-section of tube-bundle channels, it is shown that there might be different flow patterns in different sub-channels. The flow pattern transitions exhibit unsynchronized in different sub-channels. On the basis of experimental research, the flow pattern map is drawn and analyses are made on the comparison of differences between boiling flow patterns in circular tubes and those in tube-bundle channels.

A Mechanistic Model for Predicting Pressure Drop in Vertical Upward Two-Phase Flow

1999 ◽  
Vol 121 (1) ◽  
pp. 1-8 ◽  
Author(s):  
J. O̸. Tengesdal ◽  
C. Sarica ◽  
Z. Schmidt ◽  
D. Doty
Keyword(s):  
Pressure Drop ◽  
Flow Pattern ◽  
Two Phase Flow ◽  
Mechanistic Model ◽  
Flow Patterns ◽  
Phase Flow ◽  
Two Phase ◽  
Wide Range ◽  
Annular Flows ◽  
Churn Flow

A comprehensive mechanistic model is formulated to predict flow patterns, pressure drop, and liquid holdup in vertical upward two-phase flow. The model identifies five flow patterns: bubble, dispersed bubble, slug, churn, and annular. The flow pattern prediction models are the Ansari et al. (1994) model for dispersed bubble and annular flows, the Chokshi (1994) model for bubbly flow, and a new model for churn flow. Separate hydrodynamic models for each flow pattern are proposed. A new hydrodynamic model for churn flow has been developed, while Chokshi’s slug flow model has been modified. The Chokshi and Ansari et al. models have been adopted for bubbly and annular flows, respectively. The model is evaluated using the expanded Tulsa University Fluid Flow Projects (TUFFP) well data bank of 2052 well cases covering a wide range of field data. The model is also compared with the Ansari et al., (1994), Chokshi (1994), Hasan and Kabir (1994), Aziz et al. (1972), and Hagedorn and Brown (1964) methods. The comparison results show that the proposed model performs the best and agrees well with the data.

scholarly journals Characterizing the correlations between local phase fractions of gas–liquid two-phase flow with wire-mesh sensor

2016 ◽  
Vol 374 (2070) ◽  
pp. 20150335 ◽  
Author(s):  
C. Tan ◽  
W. L. Liu ◽  
F. Dong
Keyword(s):  
Flow Pattern ◽  
Two Phase Flow ◽  
Three Dimensional ◽  
Flow Patterns ◽  
Wire Mesh ◽  
Phase Flow ◽  
Local Phase ◽  
Two Phase ◽  
Phase Fluctuations ◽  
Flow Pattern Transition

Understanding of flow patterns and their transitions is significant to uncover the flow mechanics of two-phase flow. The local phase distribution and its fluctuations contain rich information regarding the flow structures. A wire-mesh sensor (WMS) was used to study the local phase fluctuations of horizontal gas–liquid two-phase flow, which was verified through comparing the reconstructed three-dimensional flow structure with photographs taken during the experiments. Each crossing point of the WMS is treated as a node, so the measurement on each node is the phase fraction in this local area. An undirected and unweighted flow pattern network was established based on connections that are formed by cross-correlating the time series of each node under different flow patterns. The structure of the flow pattern network reveals the relationship of the phase fluctuations at each node during flow pattern transition, which is then quantified by introducing the topological index of the complex network. The proposed analysis method using the WMS not only provides three-dimensional visualizations of the gas–liquid two-phase flow, but is also a thorough analysis for the structure of flow patterns and the characteristics of flow pattern transition. This article is part of the themed issue ‘Supersensing through industrial process tomography’.

scholarly journals Flow Pattern Map of Flow Boiling in a Rectangular Channel Filled with Porous Media

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2440
Author(s):  
Youngwoo Kim ◽  
Dae Yeon Kim ◽  
Kyung Chun Kim
Keyword(s):  
Porous Media ◽  
Flow Pattern ◽  
Flow Regime ◽  
Annular Flow ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Flow Patterns ◽  
Flow Pattern Map ◽  
Mist Flow ◽  
Churn Flow

A flow visualization study was carried out for flow boiling in a rectangular channel filled with and without metallic random porous media. Four main flow patterns are observed as intermittent slug-churn flow, churn-annular flow, annular-mist flow, and mist flow regimes. These flow patterns are clearly classified based on the high-speed images of the channel flow. The results of the flow pattern map according to the mass flow rate were presented using saturation temperatures and the materials of porous media as variables. As the saturation temperatures increased, the annular-mist flow regime occupied a larger area than the lower saturation temperatures condition. Therefore, the churn flow regime is narrower, and the slug flow more quickly turns to annular flow with the increasing vapor quality. The pattern map is not significantly affected by the materials of porous media.

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