On the use of area-averaged void fraction and local bubble chord length entropies as two-phase flow regime indicators

This work describes the application of an artificial neural network to process the signals measured by local conductivity probes and classify them into their corresponding global flow regimes. Experiments were performed in boiling upward two-phase flow in a vertical annulus. The inner and outer diameters of the annulus were 19.1 mm and 38.1 mm, respectively. The hydraulic diameter of the flow channel, DH, was 19.0 mm and the total length is 4.477 m. The test section was composed of an injection port and five instrumentation ports, the first three were in the heated section (z/DH = 52, 108 and 149 where z represents the axial position) and the upper ones in the unheated sections (z/DH = 189 and 230). Conductivity measurements were performed in nine radial positions for each of the five ports in order to measure the bubble chord length distribution for each flow condition. The measured experiment matrix comprised test cases at different inlet pressure, ranging from 200 kPa up to 950 kPa. A total number of 42 different flow conditions with superficial liquid velocities from 0.23 m/s to 2.5 m/s and superficial gas velocities from 0.002 m/s to 1.7 m/s and heat flux from 55 kW/m2 to 247 kW/m2 were measured in the five axial ports. The flow regime indicator has been chosen to be statistical parameters from the cumulative probability distribution function of the bubble chord length signals from the conductivity probes. Self-organized neural networks (SONN) have been used as the mapping system. The flow regime has been classified into three categories: bubbly, cap-slug and churn. A SONN has been first developed to map the local flow regime (LFR) of each radial position. The obtained LFR information, conveniently weighted with their corresponding significant area, was used to provide the global flow regime (GFR) classification. These final GFR classifications were then compared with different flow regime transition models.

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Impedance-Based Void Fraction Measurement and Flow Regime Identification in Microchannel Flows

ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, MEMS and NEMS: Volume 2 ◽

10.1115/ipack2011-52116 ◽

2011 ◽

Author(s):

Sidharth Paranjape ◽

Susan N. Ritchey ◽

Suresh V. Garimella

Keyword(s):

Flow Regime ◽

Void Fraction ◽

High Speed ◽

Electrical Impedance ◽

Two Phase Flow ◽

Phase Distribution ◽

Electrical Conductance ◽

Statistical Characteristics ◽

Phase Flow ◽

Two Phase

Electrical impedance of a two-phase mixture is a function of void fraction and phase distribution. The difference in the electrical conductance and permittivity of the two phases can be exploited to measure electrical impedance for obtaining void fraction and flow regime characteristics. An electrical impedance meter is constructed for the measurement of void fraction in microchannel two-phase flow. The experiments are conducted in air-water two-phase flow under adiabatic conditions. A transparent acrylic test section of hydraulic diameter 780 micrometer is used in the experimental investigation. The impedance void meter is calibrated against the void fraction measured using analysis of images obtained with a high-speed camera. Based on these measurements, a methodology utilizing the statistical characteristics of the void fraction signals is employed for identification of microchannel flow regimes.

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On the Damping in Tube Arrays Subjected to Two-Phase Cross-Flow

Journal of Pressure Vessel Technology ◽

10.1115/1.4023421 ◽

2013 ◽

Vol 135 (3) ◽

Cited By ~ 4

Author(s):

J. E. Moran ◽

D. S. Weaver

Keyword(s):

Flow Regime ◽

Void Fraction ◽

Two Phase Flow ◽

Cross Flow ◽

Working Fluid ◽

Exponential Fitting ◽

Phase Flow ◽

Two Phase ◽

Tube Arrays ◽

Half Power

An experimental study was conducted to investigate the mechanism of damping in tube arrays subjected to two-phase cross-flow, mainly focusing on the influence of void fraction and flow regime. The model tube bundle had a parallel-triangular configuration, with a pitch ratio of 1.49. The two-phase flow loop used in this research utilized Refrigerant 11 as the working fluid, which better models steam-water than air-water mixtures in terms of vapour-liquid mass ratio as well as permitting phase changes due to pressure fluctuations. The void fraction was measured using a gamma densitometer, introducing an improvement over the homogeneous equilibrium model (HEM). Three different damping measurement methodologies were implemented and compared in order to obtain a more reliable damping estimate: the traditionally used half-power bandwidth, the logarithmic decrement and an exponential fitting to the tube decay response. The experiments showed that the half-power bandwidth produces higher damping values than the other two methods, due to the tube frequency shifting triggered by fluctuations in the added mass and coupling between the tubes, which depend on void fraction and flow regime. The exponential fitting proved to be the more consistent and reliable approach to estimating damping. A dimensional analysis was carried out to investigate the relationship between damping and two-phase flow related parameters. As a result, the inclusion of surface tension in the form of the capillary number appears to be useful when combined with the two-phase component of the damping ratio (interfacial damping). A strong dependence of damping on flow regime was observed when plotting the interfacial damping versus the void fraction, introducing an improvement over the previous results obtained by normalizing the two-phase damping, which does not exhibit this behavior.

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Damping and Hydrodynamic Mass of a Cylinder in Simulated Two-Phase Flow

Journal of Mechanical Design ◽

10.1115/1.3254791 ◽

1980 ◽

Vol 102 (3) ◽

pp. 597-602 ◽

Cited By ~ 26

Author(s):

L. N. Carlucci

Keyword(s):

Flow Regime ◽

Void Fraction ◽

Single Phase ◽

Two Phase Flow ◽

Phase Flow ◽

Single Phase Flow ◽

Two Phase ◽

Mixture Density ◽

Void Fractions ◽

Fixed Cylinder

This paper describes the results of experiments conducted to determine the damping and hydrodynamic mass characteristics of a fixed-fixed cylinder both in liquid and in simulated two-phase flows. It was observed that damping was significantly higher in two-phase flow than in single phase flow, and that, depending on the flow regime, it exhibited a maximum or maxima at void fractions of 30% to 60%. The hydrodynamic mass was observed to decrease with increasing void fraction but at a higher rate than that of the mixture density.

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Research on the Air-Water Flow Regime and Characteristics in Rectangular Channel

10.1115/icone28-66238 ◽

2021 ◽

Author(s):

Qingche He ◽

Liangming Pan ◽

Luteng Zhang ◽

Meiyue Yan ◽

Wangtao Xu

Keyword(s):

Flow Regime ◽

Void Fraction ◽

Slug Flow ◽

Clustering Algorithm ◽

Two Phase Flow ◽

Rectangular Channel ◽

Interfacial Structure ◽

Phase Flow ◽

Two Phase ◽

Rectangular Channels

Abstract Two-phase Flow is widely involved in reactor design and is directly relevant to reactor safety. However, the flow regime in narrow rectangular channels still needs further study because it has a considerable difference from tube and bundle channels. To investigate the two-phase flow regime and interfacial structure characteristics, the air-water experiment with an adiabatic vertical channel of 4 × 66 × 1800, 6 × 66 × 1800 mm have been conducted under atmosphere pressure condition. The impedance void meter was used to measure the global void fraction in narrow rectangular channels. A high-speed camera was used to record the profiles of the flow regime. The flow regime was identified by the random forest clustering algorithm based on a training sample. The profiles of different parameters, including void fraction, pressure loss at Z/D = 150, were analyzed in this paper. Furthermore, based on the parameters’ distribution, the regime transition criteria in narrow rectangular channels were discussed. It is shown that the transition from bubble to slug flow always occurred when the average void fraction is 0.17–0.2. The transition value is 0.57–0.62 when the slug Flow changes to the churn-turbulent Flow and 0.78–0.8 from churn-turbulent to annular Flow. The constant used in the Lockhart-Martinelli correlation is found to calculate the frictional pressure drop in a rectangular channel. Furthermore, the drift-model applied to the rectangular channel is verified.

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Void Fraction, Pressure Drop, and Flow Pattern Behavior for Two-Phase Non-Newtonian Slug Flow

10.1115/omae2021-62513 ◽

2021 ◽

Author(s):

Faraj Ben Rajeb ◽

Syed Imtiaz ◽

Yan Zhang ◽

Amer Aborig ◽

Mohamed M. Awad ◽

...

Keyword(s):

Pressure Drop ◽

Flow Pattern ◽

Flow Regime ◽

Void Fraction ◽

Slug Flow ◽

Two Phase Flow ◽

Flow Patterns ◽

Intermittent Flow ◽

Phase Flow ◽

Two Phase

Abstract Slug flow is one of the most common flow patterns in non-Newtonian two-phase flow in pipes. It is a very common occurrence in gas-liquid two-phase flow in the pipe. Usually, it is an unfavorable flow pattern due to its unsteady nature, intermittency as well as high pressure drop. The differences between slug flow and elongated bubble flow are not clear because usually these two types of flow combined under one flow category. In general, these two-phase flow regimes are commonly defined as intermittent flow. In the present study, pressure gradient, and wave behavior in slug flow have been investigated depending on experimental work. In addition, void fraction has been estimated regarding available superficial liquid and gas velocities. The experimental records of superficial velocities of gas and liquid for slug flow and other flow patterns is used to create flow regime map for the gas non-Newtonian flow system. The effect of investigated flow regime velocities for non-Newtonian/gas flow on pressure drop and void fraction is reported. Pressure drop has been discovered to be reduced in slug flow more than other flow patterns due to high shear thinning behavior.

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Visualization Study of Gas-Liquid Two-Phase Flow in a Hydrophobic Pipe

Volume 1: Symposia, Parts A and B ◽

10.1115/fedsm2007-37101 ◽

2007 ◽

Author(s):

Takayoshi Kikuchi ◽

Tatsuya Hazuku ◽

Yutaka Fukuhara ◽

Tomoji Takamasa ◽

Takashi Hibiki

Keyword(s):

Flow Regime ◽

Void Fraction ◽

Gas Flow ◽

Two Phase Flow ◽

Flow Characteristics ◽

Phase Flow ◽

Two Phase ◽

Experimental Conditions ◽

Churn Flow ◽

Effect Of Surface

To evaluate the effect of pipe wall surface wettability on flow characteristics in a vertical upward gas-liquid two-phase flow, a visualization study was performed using an acrylic pipe and a hydrophobic pipe. Such basic flow characteristics as flow patterns, pressure drop and void fraction were investigated in these pipes. In the hydrophobic pipe, an inverted-churn flow regime was observed in a region where the churn flow regime was observed in the acrylic pipe, while a droplet flow regime was observed in the region where an annular flow regime was observed in the acrylic pipe. At a high gas flow rate, the average void fraction in the hydrophobic pipe was higher than in the acrylic pipe. The effect of surface wall wettability on frictional pressure loss was confirmed to be insignificant under the present experimental conditions.

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Damping of Tubes With Internal Two-Phase Flow

Volume 9: 6th FSI, AE and FIV and N Symposium ◽

10.1115/pvp2006-icpvt-11-93881 ◽

2006 ◽

Author(s):

Alexandre Gravelle ◽

Annie Ross ◽

Michel J. Pettigrew ◽

Njuki W. Mureithi

Keyword(s):

Flow Regime ◽

Void Fraction ◽

Two Phase Flow ◽

Damping Ratio ◽

Strong Dependence ◽

Internal Flow ◽

Piping System ◽

Phase Flow ◽

Two Phase ◽

Phase Damping

Two-phase internal flow is present in many piping system components. Although two-phase damping is known to be a significant constituent of the total damping, the energy dissipation mechanisms that govern two-phase damping are not well understood. In this paper, damping of vertical clamped-clamped tubes subjected to two-phase air-water internal flow is investigated. Experimental data is reported, showing no dependence of two-phase damping on tube natural frequency, and a strong dependence on void fraction, flow velocity and flow regime. Two-phase damping increases with void fraction, reaches a maximum, and decreases beyond that point. The maximum damping ratio is roughly 3% for all flow velocities. It is reached at around 50% void fraction for high velocities, and 25% void fraction for low velocities. Data points plotted on two-phase flow pattern maps indicate that damping is greater in a bubbly flow regime than it is in a slug or churn regime. The maximum two-phase damping is reached at the highest void fraction before the transition to a slug or churn flow regime. It appears that two-phase damping may depend on the interface surface area between phases.

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