Two-phase Flow In Vertical Tube Research Articles

Comparison of Standalone and Hybrid Machine Learning Models for Prediction of Critical Heat Flux in Vertical Tubes

Critical heat flux (CHF) is an essential parameter that plays a significant role in ensuring the safety and economic efficiency of nuclear power facilities. It imposes design and operational restrictions on nuclear power plants due to safety concerns. Therefore, accurate prediction of CHF using a hybrid framework can assist researchers in optimizing system performance, mitigating risk of equipment failure, and enhancing safety measures. Despite the existence of numerous prediction methods, there remains a lack of agreement regarding the underlying mechanism that gives rise to CHF. Hence, developing a precise and reliable CHF model is a crucial and challenging task. In this study, we proposed a hybrid model based on an artificial neural network (ANN) to improve the prediction accuracy of CHF. Our model leverages the available knowledge from a lookup table (LUT) and then employs ANN to further reduce the gap between actual and predicted outcomes. To develop and assess the accuracy of our model, we compiled a dataset of around 5877 data points from various sources in the literature. This dataset encompasses a diverse range of operating parameters for two-phase flow in vertical tubes. The results of this study demonstrate that the proposed hybrid model performs better than standalone machine learning models such as ANN, random forest, support vector machine, and data-driven lookup tables, with a relative root-mean-square error (rRMSE) of only 9.3%. We also evaluated the performance of the proposed hybrid model using holdout and cross-validation techniques, which demonstrated its robustness. Moreover, the proposed approach offers valuable insights into the significance of various input parameters in predicting CHF. Our proposed system can be utilized as a real-time monitoring tool for predicting extreme conditions in nuclear reactors, ensuring their safe and efficient operation.

Flow Pattern and Transformation Mechanism of Upward Gas-Liquid Two-Phase Flow in Vertical Tubes Under Undulating Vibration

Flow Pattern and Transformation Mechanism of Upward Gas-Liquid Two-Phase Flow in Vertical Tubes Under Undulating Vibration

A new correlation for the prediction of critical quality in tubes

In this paper, dryout phenomenon of steam-liquid two-phase flow in vertical tube is studied. Based on Becker’s experimental data, 393 points of dryout data with pressure ranging from 2.9 to 20.1 MPa, mass flow rate ranging from 496 to 3120 kg/(m2 s), heat flux less than 1268 kW/m2 and pipe diameter ranging from 10 to 24.7 mm are re-fitted, and a new correlation for predicting the critical quality is proposed. The MAE of the new correlation is 7.2% when predicting the Becker's data. It also positively correlated with other databases of steam-liquid critical quality. However, the prediction accuracy of the new correlation is relatively low for refrigerant and deformation channel, which will be further revised in future work.

Identification of flow regimes using conductivity probe signals and neural networks for counter-current gas–liquid two-phase flow

A rigorous experimental investigation has been carried out on counter-current air–water two-phase flow in vertical tube with circular cross-section over a wide range of phase flow rates of air and water. It is a novel attempt to capture, identify and predict the individual flow regimes for different combinations of air and water superficial velocities based on some of its objective descriptions. Two different conductivity probes (parallel wire and ring probes) have been designed to collect objective descriptions of the flow regime in terms of the time series voltage signals. Statistical analyses have been carried out to characterize those time series voltage signals in terms of some statistical parameters. Three methodologies have been developed using a genetic algorithm (GA)-tuned multi-layer feed-forward neural network with back-propagation algorithm (GA-MLFFNN), a GA-tuned multi-layer radial basis function neural network with entropy-based clustering and back-propagation algorithm (GA-MLRBFNN–EC) and lastly, a GA-tuned multi-layer radial basis function neural network with fuzzy C-means clustering and back-propagation algorithm (GA-MLRBFNN–FCMC) to predict the different flow regimes after knowing the objective descriptions of the flow pattern in terms of the statistical parameters. Parallel wire conductivity probe is found to be better to capture the objective signature of the individual flow regime. GA-MLRBFNN–EC is found to be the best to predict flow regimes successfully.

Helical Capacitance Sensor-Based Gas Fraction Measurement of Gas–Liquid Two-Phase Flow in Vertical Tube With Small Diameter

A helical capacitance sensor for gas fraction including void fraction and volumetric void fraction measurement of gas-liquid two-phase flow in a vertical tube of 5 mm in diameter is presented in this paper. The structure of the helical capacitance sensor is optimized using a finite element method to achieve a homogeneous sensitivity field distribution. A calibration device using the quick closing valve method is designed and used to calibrate the void fraction measurement. Experiment results show that the relative error of gas fraction is less than 10%. The reason for the nonlinearity between the sensor output and gas fraction to be measured is discussed. The linear model describing the relationship between capacitance and gas fraction is obtained by removing the wall capacitance.

Local Flow Regime Transition Criteria of Gas-Liquid Two-phase Flow in Vertical Upward Tube with a Horizontal Rod

The upward multiphase cross flow and heat transfer in the vertical tube may occur in oil production and chemical facilities. In this study, the local flow patterns of an upward gas-water two phase cross flow in a vertical tube with a horizontal rod have been investigated with an optical probe and the digital high speed video system. The local flow patterns are defined as the bubble, slug, churn and annular flow patterns. Optical probe signals are analyzed in terms of probability density function, and it is proved that the local flow patterns can be recognized by this method. The transition mechanisms between the different flow patterns have been analyzed and the corresponding transitional models are proposed. Finally, local flow pattern maps of the upward gas-water two-phase flow in the vertical tube with a horizontal rod are constructed.

1509 垂直管内気液二相流のボイド率断面分布計測と拡張二流体モデルの検証

1509 垂直管内気液二相流のボイド率断面分布計測と拡張二流体モデルの検証

The flow characteristics of an upward gas‐liquid two‐phase flow in a vertical tube with a wire coil: Part 1. Experimental results of flow pattern, void fraction, and pressure drop

AbstractExperiments were carried out to investigate the flow pattern, average void fraction, and pressure drop of an upward air‐water two‐phase flow in vertical tubes of 25‐mm inside diameter with wire coils of varying wire diameter, pitch, and number of coils in cross section. Five kinds of flow patterns—bubble, slug, churn, semiannular, and annular flow—were defined based on the observation of flow behavior in the experiments. At higher water flowrates, the bubble‐to‐slug transition occurred at lower air flowrates in tubes with wire coils than in smooth tubes. The average void fraction was found by using the drift flux model. Further, the experimental results of the friction pressure drop were compared with the Lockhart‐Martinelli correlation. As a result, a correlation with the constant C in Chisholm's equation was obtained as a function of the wire coil pitch‐to‐diameter ratio. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(8): 639–651, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10066

The flow characteristics of an upward gas‐liquid two‐phase flow in a vertical tube with a wire coil: Part 2. Effect on void fraction and liquid film thickness

AbstractAn experimental study has been carried out to clarify the characteristics of the void fraction and the liquid film thickness of the air‐water two‐phase flow in vertical tubes of 25‐mm inside diameter with wire coils of varying wire diameter and pitch. The flow pattern in the experiment on the average void fraction and the local void fraction distribution in cross section was a bubble flow, and the liquid film thickness was in the region of semiannular and annular flows. It is clarified from these experiments that the average void fraction in tubes with wire coils is lower than that in a smooth tube and decreases with the wire diameter owing to the centrifugal force of the swirl flow which concentrates bubbles at the center of the tube, that the local liquid film thickness becomes more uniform with a decrease in the pitch of the wire coil, and that the liquid film becomes thicker after the passage through the wire coil with an increase in the wire diameter. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(8): 652–664, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10067

Flow Characteristics of Upward Gas-Liquid Two-Phase Flow in a Vertical Tube with a Wire Coil. 1st Report. Experimental Results of Flow Pattern, Void Fraction and Pressure Drop.

Experiments were carried out to investigate the flow pattern, average void fraction, and pressure drop of upward air-water two-phase flow in vertical tubes of 25 mm inside diameter with wire coils fo varying wire diameter, pitch and number of coil. Five kinds of flow patterns, i.e., bubble, slug, churn, semi-annular and annular flow, were defined based on the observation of flow behaviors in the experiments. At higher water flow rate, the bubble-slug transition occurred at a lower air flow rate in tubes with wire coil than in the smooth tube. The average void fraction was clarified using the drift flux model. Furthermore, the experimental results of the friction pressure drop were compared with the Lockhart-Martinelli correlation. As a result, a correlation for the constant C in Chisholm's equation was obtained as a function of wire coil pitch-to-diameter ratio.

Flow Characteristics of Upward Gas-Liquid Two-Phase Flow in a Vertical Tube with a Wire Coil. 2nd Report. Effect on Void Fraction and Liquid Film Thickness.

An experimental study has been carried out to clarify the characteristics of the void fraction and liquid film thickness of air-water two-phase flow in vertical tubes of 25 mm inside diameter with wire coil of varying wire diameter and pitch. Flow pattern in the experiment of average void fraction and local void fractrion distribution in a cross section is bubble flow, and liquid film thickness is in the region of semi-annular and annular flow. It is clarified from these experiments that the average void fraction in tubes with a wire coil is lower than that of the smooth tube and decreases with the wire diameter owing to the centrifugal force of swirl flow which concentrates bubbles at the center of the tube, and the liquid film thickness between the wire coil is uniformed with the decrease of the pitch of wire coil and that liquid film becomes thicker after the passage of wire coil with the increase of the wire diameter.

Convective heat-transfer mechanism in two-phase flows for high concentrations of finely dispersed solid particles

A model is proposed for convective heat transfer and an analytic solution is obtained for the energy equation for a two-phase flow in vertical tubes with high concentrations of finely dispersed solid particles.

Flow patterns in vertical two-phase flow

This paper is concerned with the flow patterns which occur in upwards gas-liquid two-phase flow in vertical tubes. The basic flow patterns are described and the use of flow pattern maps is discussed. The transition between plug flow and churn flow is modelled under the assumption that flooding of the falling liquid film limits the stability of plug flow. The resulting equation is combined with other flow pattern transition equations to produce theoretical flow pattern maps, which are then tested against experimental flow pattern data. Encouraging agreement is obtained.

Flow regime transition criteria for upward two-phase flow in vertical tubes

Traditional two-phase flow-regime criteria based on the gas and liquid superficial velocities may not be suitable to the analyses of rapid transient or entrance flows by the two-fluid model. Under these conditions, it is postulated that direct geometrical parameters such as the void fraction are conceptually simpler and therefore more reliable parameters to be used in flow-regime criteria than the traditional parameters. From this point of view, new flow-regime criteria for upward gas-liquid flow in vertical tubes have been developed considering the mechanisms of flow-regime transitions. These new criteria can be compared to existing criteria and experimental data under steady-state and fully developed flow conditions by using relative velocity correlations. The criteria showed reasonable agreements with the existing data for atmospheric air-water flows. Further comparisons with data for steam—water in round tubes and a rectangular channel at relatively high system pressures have been made. The results confirmed that the present flow-regime transition criteria could be applied over wide ranges of parameters as well as to boiling flow.

Characteristics of Counter current Gas-Liquid Two-Phase Flow in Vertical Tubes

Investigations into the flow pattern and the void fraction for countercurrent air-water flow in vertical tubes of diameter D = 40 and 80 mm were reported. The flow maps were presented and showed slug flow regime occupied larger portion on them. The void fraction was measured by the quick-closing valve technique, in bubbly and slug flow regime. The void fraction data available in the literatures as well as present work for counter- current flow in vertical tubes were correlated in terms of dimensionless groups. The experimental results of the present work were also compared with the drift flux model.

Characteristics of countercurrent gas-liquid two-phase flow in vertical tubes.

Investigations into the flow pattern and the void fraction for countercurrent air-water flow in vertical tubes of diameter D = 40 and 80 mm were reported. The flow maps were presented and showed slug flow regime occupied larger portion on them. The void fraction was measured by the quick-closing valve technique, in bubbly and slug flow regime. The void fraction data available in the literatures as well as present work for counter- current flow in vertical tubes were correlated in terms of dimensionless groups. The experimental results of the present work were also compared with the drift flux model.

Two-phase (gas—liquid) flow phenomena—I Pressure drop and hold-up for two-phase flow in vertical tubes

An attempt has been made to develop a theory for two-phase flow in a vertical tube when the liquid flow is annular. Published data on liquid hold-up and pressure gradient have been examined in the light of this theory together with original data obtained on air-water mixtures in a 1 2 in. diameter glass tube. Predictions of the liquid film thickness were found to be accurate to ± 15 per cent. The theory also predicted the flow conditions under which annular flow gave way to slug flow. An approach has been made to an empirical correlation of friction factors at the gas-liquid interface.