Horizontal Two-phase Flow Research Articles

An experimental approach to heat loss measurement of horizontal two-phase flow boiling in low-pressure low-flow (LPLF) conditions

A crucial parameter remarkably influencing the reliability and accuracy of vapor quality measurements in flow boiling experiments is the measurement of heat loss. The latent heat loss estimation in two-phase flow boiling sounds more demanding than that of sensible heat loss in single-phase flow experiments. To accurately investigate the impact of vapor quality on the heat transfer coefficient of flow boiling, accurate estimates of heat loss and subsequent calibration of heat supplies are of a great significance. It is widely common that the single-phase flow tests are performed to estimate a fixed heat loss percentage and calibrate heat supplies for further measurements of vapor quality and heat transfer coefficient of flow boiling experiments. In the present work, an empirical methodology is first proposed to measure heat losses and calibrate latent heat supplies directly from flow boiling process. The proposed methodology is then compared and verified with the commonly applied methodology which uses single-phase flow experiments. The proposed methodology exhibited higher accuracy than the single-phase-based methodology to estimate heat losses and measure vapor quality within two-phase flow boiling under low-pressure low-flow (LPLF) operating conditions.

An explicit approximation of the central angle for the curved interface in double-circle model for horizontal two-phase stratified flow

Stratified flow in horizontal tubes is frequently observed in gas-liquid two-phase flow system. In the two-fluid modeling, it is important to define the interface shape in solving the balance equations to determine the key parameters such as the interfacial transfer terms, void fraction, and pressure drop. A double-circle model is usually introduced to depict the concave-down interface in a horizontal circular tube under the stratified-wavy flow condition. However, calculation of the central angle in the double-circle model, which represents the interfacial curvature, requires an appropriate iterative numerical root-finding scheme to solve the implicit transcendental equation. In this study, an explicit approximate equation has been proposed without requirement of the iterative scheme and numerical instability, which is expected to improve the coding process and computation efficiency in the analysis code with the two-fluid model.

Influence of a restriction on flow patterns, void fraction, and pressure drop in gas–liquid pipe flow

Subsurface safety valves play an important role in the hydrocarbon production process. The Brazilian industry is suffering significant losses due to the reduction of the useful life of this device, not to mention the risks associated with the operation and the environment. One possible reason for the failure of the subsurface safety valve’s reliability prediction may be the occurrence of two-phase flow in the well. For this reason, a set of twenty horizontal two-phase flow experiments was carefully designed to evaluate the influence of a simplified internal reduction in a steel pipe. Superficial velocities were considered in the range of 0.1 m/s and 2.0 m/s for water and, 0.33 m/s and 7.47 m/s for compressed air. The experiments were carried out in 2″-i.d. and 2-m-long steel pipes, being a tube with restriction and another without restriction. Both tubes have an upstream development length of 126 pipe diameters. Gamma-ray densitometry and a differential pressure transducer were used to measure void fraction and pressure drop, and a visualization window was used to observe the flow patterns. Among the main findings are the effects of void fraction and mixture velocity on pressure gradient, with different impacts on the restricted pipe (RP) compared to the unrestricted pipe (UP). The presence of the restriction generated significant changes in the upstream flow: the lengths of the liquid slugs were increased, appeased by the increase in local pressure necessary to overcome the resistance produced by the restriction. Downstream, the change was reflected in the rise of void fraction and decrease of slip ratio between the phases.

Condensation Heat Transfer and Pressure Drop of Acoustically Actuated Horizontal Two-Phase Flow

An acoustic actuation technique to enhance condensation inside horizontal tubes is developed and experimentally demonstrated. Heat exchanger headers are used as Helmholtz resonators, allowing low-frequency (∼10 Hz) acoustic waves to propagate and be reflected within the condenser, improving mixing saturated vapor and condensed liquid, thereby enhancing heat transfer. Heat transfer coefficients and pressure drops are measured to evaluate the heat transfer enhancement and pressure drop penalty as a function of vapor quality, mass flux, temperature difference, and acoustic wave amplitude and frequency. Experiments are conducted using a tube-in-tube heat exchanger with an inner diameter of 14.45 mm that partially condenses refrigerant R134a at 950 kPa across vapor qualities ranging from 5% to 80% as mass fluxes of 120 and 180 kg m−2 s−1 and temperature differences of 6 and 12 K. The actuation amplitude and frequency are varied from 0.5 to 6 mm and 2 – 20 Hz, respectively to characterize the acoustic response. Heat transfer enhancement mechanisms are hypothesized and evaluated based on the experimental results, concluding that changes in two-phase flow patterns and increased convective effects lead to significant enhancement at low qualities but negligible enhancement at high qualities when the flow is annular. Existing correlations and modifications to existing models are proposed to explain the observed enhancement, and a simple correlation based on a heat-and-momentum analogy is proposed, which predicts both baseline and enhanced heat transfer data within 2.7%.

Characterization of local parameters of inclined upward air–water bubbly two-phase flows in a round pipe

The present work seeks to develop a detailed experimental database and characterize the local effects of inclination on horizontal and upward bubbly air–water two-phase flows. Experimental conditions are selected to investigate bubbly flows at a variety of orientations while reducing the influence of flow regime transition. Detailed time-averaged data is collected using state-of-the-art four-sensor conductivity probes for measurements across the flow area for five flow conditions at five inclination orientations in a 25.4 mm inner diameter pipe. Using the newly established database, effects of inclination on bubbly flows are analyzed, as are changes in liquid and gas flow rate at different orientations. The observations include (1) bubble migration and agglomeration at the top pipe wall as orientation changes from vertical to horizontal; (2) reducing the angle from vertical reduces the local gas velocity, and correspondingly reduces the global slip from greater than unity at 90° to less than unity for 60° and lower; (3) changes in the bubble size distribution are primarily at the interface between the bubble cluster and the liquid region of the pipe, not coalescence within the bubble cluster. Physical mechanisms for these observations are proposed, and the present trends at different orientations support previous experiments in horizontal two-phase flows.

Modeling of sand transport and elbow erosion in horizontal two-phase slug flow

Horizontal wells play an important role in maximizing the recovery of hydrocarbons from oil and gas reservoirs. During production, if the rate of production of produced fluids with sand particles is low, the deposition of sand particles in horizontal flow lines can wreak havoc on production systems in such a way as to cause increased pressure loss and reduction or loss of production when the pipe is partially or completely blocked. On the other hand, if the production rate of fluids is high, the impact of sand particles on the wall of the pipe will erode the inner surface of the pipe fittings. In this case, erosion can be severe enough to cause a hazardous spill and complete shutdown of systems. Therefore, it is important to quantify the sand transport and erosivity of different flow regimes. Under moderate velocities, there exists a flow regime which is called slug flow which is characterized by the intermittent appearance of liquid slugs propagating through the pipe. Studying the sand deposition and erosion due to sand particles entrained in intermittent flows is extremely difficult since the solid particle velocity magnitudes are coupled with several multiphase flow parameters such as phase distribution and slippage between the phases. This work focuses on the improvement of mechanistic models for predicting critical deposition of sand particles in horizontal pipes and erosion in horizontal-horizontal elbows. In this investigation, a modified model is proposed to better predict the critical deposition velocity and the characteristic particle velocity as a function of the slug flow characteristics. The model predictions are compared with the sand transport and erosion data collected at the University of Tulsa and other research institutions. The results show that the new approach provides improved predictions for sand transport and maximum erosion in standard elbows when compared with existing models.

Improvement of entrainment model for horizontal flow in ATHLET and application to Mantilla experiment and TPTF

The entrainment correlations proposed by Al-Sarkhi & Sarica (2013) and the modified Pan & Hanratty (Lee, 2022) were newly implemented in ATHLET to improve the entrainment model for horizontal flows. In addition, the criterion for the onset of entrainment was adjusted with the model suggested by Ishii & Grolmes (1975). The implemented models were examined by simulating two horizontal two-phase flow experiments, the Mantilla experiment and TPTF, in the frame of a benchmark activity of FONESYS. The Mantilla experiment consisted of 2-inch and 6-inch diameter pipes, and it was conducted with air–water mixtures at ∼ 2 bar pressures and ∼ 20 °C temperatures. On the other hand, TPTF had 4-inch and 8-inch diameter test sections, and it was performed with highly pressurized steam-water mixtures in 30 – 86 bar. It turns out that the Al-Sarkhi & Sarica model could improve the prediction of entrainment for the 2-inch Mantilla test section, but it predicted much higher entrainment fractions for the 6-inch Mantilla test section and TPTF. On the other hand, the modified Pan & Hanratty correlation could achieve significant improvements for the entrainment prediction for both the Mantilla experiment and TPTF. Regarding the onset of entrainment, the Ishii & Grolmes criterion was able to yield a slightly better prediction than the ATHLET built-in model for high-pressure cases of TPTF.

Pressure Drop in Horizontal Two-Phase Flow

In an artificial environment, the most important key in the process equipment design is determining gas-liquid two-phase flow frictional pressure drop of pipes. To achieve this, an experimental investigation was carried out in this study to analyze the pressure drops of air-water two-phase flow in a 30mm internal diameter horizontal pipe with a length of 6m at different flow conditions. The study was carried out at 20Co using tap water and air. To cover the slug flow pattern, the volumetric flow rate of water varied from 30 to 80 LPM, and the volumetric flow rate of air from 40 to 200 LPM. Pressure transmitters were used to measure pressure at four different points along the test section, each 2m apart. The results of the experiments were compared to 8 models using 3 distinct methods: Mean Absolute Percentage Error (MAPE), Relative Performance Factor (RPF), and the percentage of data included in the range of the 30% error band. All methods produced similar results, with the Sun-Mishima model being the most accurate.

Gas-Liquid Two-Phase Flow Regime in a Horizontal Channel Under Transverse Vibration

This paper presents experiments carried out to study the influences of transverse vibration on horizontal gas-liquid two-phase flow. The experiments considered the transverse vibration over a wide range of vibration frequencies and vibration amplitudes. Five typical flow regimes were observed. The fluid flow conditions in steady state and transverse vibration were compared. The traditional flow regime transition lines did not match the gas-liquid flow in channel under transverse vibration. The results suggest that vibration frequency mainly affected the flow regime by promoting the aggregation of gas slug, while vibration amplitude mainly influenced the fluctuation height of the gas and liquid interface.

Liquid–Solid Two-Phase Flow Rate Measurement by Electrical and Ultrasound Doppler Sensors

Flow rate measurement in multiphase flow is essential for process control and safety production. As the drawbacks of conventional flowmeter measurement error produced by the heterogeneous phase or velocity distribution, a measurement technique combining an electrical resistance tomography (ERT) and an ultrasound Doppler (UD) sensor is proposed. The UD sensor obtains the dispersed particle velocity distribution, and the ERT acquires the solid phase distribution. An experimental platform is constructed for the liquid-solid two-phase horizontal flow experiments. The dual-plane ERT with the cross-correlation signal analysis compensates for the inaccurate particle velocity measurement at the bottom of the pipe by using UD independently due to the locally high concentration. The liquid-solid two-phase mixed flow rate under different flow regimes is measured with the two sensors. The proposed method has a 6.3% maximum uncertainty for the liquid-solid two-phase flow rate measurement.

Partition method of wall friction and interfacial drag force model for horizontal two-phase flows

The improvement of thermal-hydraulic analysis techniques is essential to ensure the safety and reliability of nuclear power plants. The one-dimensional two-fluid model has been adopted in state-of-the-art thermal-hydraulic system codes. Current constitutive equations used in the system codes reach a mature level. Some exceptions are the partition method of wall friction in the momentum equation of the two-fluid model and the interfacial drag force model for a horizontal two-phase flow. This study is focused on deriving the partition method of wall friction in the momentum equation of the two-fluid model and modeling the interfacial drag force model for a horizontal bubbly flow. The one-dimensional momentum equation in the two-fluid model is derived from the local momentum equation. The derived one-dimensional momentum equation demonstrates that total wall friction should be apportioned to gas and liquid phases based on the phasic volume fraction, which is the same as that used in the SPACE code. The constitutive equations for the interfacial drag force are also identified. Based on the assessments, the Rassame-Hibiki correlation, Hibiki-Ishii correlation, Ishii-Zuber correlation, and Rassame-Hibiki correlation are recommended for computing the distribution parameter, interfacial area concentration, drag coefficient, and relative velocity covariance of a horizontal bubbly flow, respectively.

Modeling of void fraction and relative velocity covariance for dispersed bubbly and intermittent flows in horizontal channels

The interfacial drag force governs the momentum exchange between gas and liquid phases and is a key parameter in predicting void fraction using a one-dimensional thermal-analysis code. The interfacial drag force is formulated by the product of the overall drag coefficient and the area-averaged relative velocity between two phases. The area-averaged relative velocity for gas-dispersed two-phase flows has been formulated with the aid of the distribution parameter, which expresses the covariance due to the distributions of void fraction and mixture volumetric flux. It has been pointed out that the term due to void fraction covariance is missing in the formulation of the area-averaged relative velocity adopted in one-dimensional thermal-analysis codes. This study has been conducted to develop void fraction and relative velocity covariance models for gas-dispersed two-phase flows in horizontal pipes. The database of local void fraction distributions for horizontal bubbly flows was established, and an artificial database for intermittent horizontal flows was modeled with assumed distributions of local void fractions. The developed void fraction covariance model for gas-dispersed horizontal two-phase flows could reproduce the data with the mean relative deviation (i.e., bias) of 8.33% and the mean absolute relative deviation (i.e., random uncertainty) of 21.4%. The developed relative velocity covariance model for gas-dispersed horizontal two-phase flows could reproduce the data with the mean relative deviation (i.e., bias) of -0.265% and the mean absolute relative deviation (i.e., random uncertainty) of 7.11%.

Uncertainty analysis for multiphase flow: A case study for horizontal air-water flow experiments

This work describes the procedure used to define the measurement uncertainties of horizontal two-phase air-water flow experiments conducted to determine influences due to pipe diameter on pressure gradient on such flows. These experiments were performed with 4 different pipe diameters, always using the same test section length, therefore varying the length-to-diameter (L/D) ratio. Several parameters were measured, such as volumetric/mass flow rate, pressures, temperatures and pressure drop; other parameters were calculated, such as the superficial velocities of each fluid, as well as their corresponding properties. The main parameters studied were the flow patterns for different velocity configurations and the two-phase pressure drop to be used for model improvement, thus the importance of uncertainties analysis. The sources of uncertainty were defined, detailed, systematically studied and quantified. Also, the reproducibility capacity of the experimental setups were analysed through the uncertainty analysis and proving them to be able for future similar studies. The flow maps with their uncertainties could help understand the thresholds for each defined flow pattern region, and the plots of two-phase pressure drop variation with diameter confirmed the homogeneous model as a possible approach to calculate pressure drop if the uncertainties are considered.

Defining the flow rates in horizontal two-phase water-gas flows and operation features of a conical narrowing device in a multiphase flowmeter with a gamma-densitometer

Defining the flow rates in horizontal two-phase water-gas flows and operation features of a conical narrowing device in a multiphase flowmeter with a gamma-densitometer

On the life and habits of gas-core slugs: characterisation of an intermittent horizontal two-phase flow

Slugs are intermittent structures observed in horizontal co-current gas-liquid two-phase flow. Published data examining horizontal flow indicate the existence of intermittent sub-flow patterns. There is limited work performed on the study of this sub-categorisation. This paper presents a method, exploiting non-intrusive Electrical Capacitance Tomography (ECT) measurements, to assess and to characterise the spatial and temporal features of horizontal gas-oil flow. A logic-based algorithm is proposed to automatically identify and classify flow regimes. This algorithm uses the spatial distribution of the phases, based on measurements of the intrinsic dielectric properties of the fluids. The measurements were performed at the NEL UK national standard multiphase flow loop using a high-speed dual-plane ECT sensor array. The ECT measurements identified intermittent liquid structures with a sustained gas-core in the central region of the pipe cross-section with outer features analogous to those of liquid slugs. Assessment of the frequency and time span of the periodic structures showed that gas-core slugs are, typically, shorter than full slug structures but are more frequent for the same given time period. For both flow structures, the mixture velocity was a determinant factor, with gas-core slugs dominating the flow at higher velocities. The experimental work led to the modification of existing flow pattern transition models. The modified flow regime maps suggested in this study aim to widen the applicability of the results by enabling the prediction of gas-core slug flow for similar experimental and operating conditions. The present work comprises the initial steps towards automatic flow regime identification in multiphase flow metering. Automatic flow regime recognition has the potential to lead to better process control and improved accuracy in production allocation.

Experimental and numerical study of air-water flow characteristics in a horizontal duct

The horizontal bubbly two-phase flow is preferably used in various industrial applications because it provides high interfacial areas which enhance the heat and mass transfer. In the present research, the phase distribution of controlled air-water flow in a horizontal acrylic round pipe with 60 mm inside diameter (D) has been investigated experimentally and modeled numerically. The modeled differential pressure and the mixture velocity profile at a distance of 33D from the mixing section (fully developed region) are computed numerically and compared with those obtained experimentally from the two-phase flow system established and maintained at the National Institute of Standards (NIS-Egypt). Furthermore, the numerical and the experimental data have been compared with previous correlations and models. Reasonable quantitative agreement between all data is found. An electronic device based on Arduino Uno board was designed and used with careful data manipulation for measuring the slug bubble velocity. The results point out that the air volume fraction has a maximum value at the upper pipe wall as the gas bubbles tend to migrate to the upper wall. A new correlation was obtained for bubble migration length to the upper pipe wall which is very important in chemical industrial processes and other engineering application.

Validation of AIAD Sub-Models for Advanced Numerical Modelling of Horizontal Two-Phase Flows

In this work, the modelling of horizontal two-phase flows within the two-fluid Euler–Euler approach is investigated. A modified formulation of the morphology detection functions within the Algebraic Interfacial Area Density (AIAD) model is presented in combination with different models for the drag force acting on a sheared gas–liquid interface. In the case of free surface flows, those closure laws are often based on experimental correlations whose applicability is limited to certain flow regimes. It is investigated here whether the implementation of the modified blending functions in ANSYS CFX avoids this limitation. The influence of the new functions on the prediction of turbulence parameters in free surface flows is also examined quantitatively for the k-ω and k-ε two-equation turbulence models. Transient simulations of the WENKA counter-current stratified two-phase flow experiment were performed for validation. A prediction of the correct flow pattern as observed in the experiment improved dramatically when a turbulence damping term was included in the standard two-equation models. Using the k-ω and a modified k-ε turbulence model with damping terms close to the interface, better agreement with the experimental data was achieved. The morphology detection mechanism of the unified blending functions within the AIAD is seen as an improvement with respect to the detection of sharp interfaces. Satisfactory quantitative agreement is achieved for the modified free surface drag. Furthermore, it is demonstrated that turbulence dampening has to be accounted for in both turbulence models to qualitatively reproduce the mean flow and turbulence quantities from the experiment.

Condensation heat transfer and pressure drop characteristics of Isobutane in horizontal channels with twisted tape inserts

• Using twisted tapes augmented the heat transfer and pressure drops. • The heat transfer rate enhanced by giving rise to vapor quality and mass flux. • The pressure losses increased by giving rise to vapor quality and mass flux. • The performance factor varied between 0.39 to 1.05 using inserts. The enhancement of heat transfer rate in heat exchangers has been considered a major concern. In this research, the impacts of inserting twisted tapes in horizontal two-phase flow heat exchangers are discussed, and different values of vapor qualities (in the range of 0.1 to 0.7) and mass velocities (in the range of 119 to 367 kgm −2 s −1 ) are considered during forced convective condensation of R600a (Isobutane). The test case is a pipe made from copper with an inner diameter of 8.1 mm and a length of 1000 mm. Furthermore, three twisted tape inserts with various twist ratios (defined as the ratio of the twisted tape pitch to the test pipe inner diameter) of 4, 10, and 15 are used. The results illustrated that installing twisted tapes results in the increment of pressure drops and the rate of heat transfer in comparison to the smooth case. Furthermore, the pressure drops and heat transfer rates augment as the refrigerant mass velocity and vapor quality increase. Depending on the inserts type and operating conditions, the performance factor (a criterion to assess the performance modification compared to the primary test case) between 0.39 to 1.05 was obtained. It was also observed that there exists an optimum amount of the refrigerant mass velocity at which the performance factor is higher. Results showed that generally using twisted tapes in heat exchangers is not instrumental unless when the main concern is to improve the heat transfer rate or when the augmented power consumed by pump can be justified.

Comparison of Dynamic Mode Decomposition and Deep Learning Techniques for Two-Phase Flows Analysis

Dynamic mode decomposition (DMD) and deep learning are data-driven approaches that allow a description of the target phenomena in new representation spaces. This fact motivates their comparison in the analysis of flow data, generated through experimental setups and numerical simulations. The focused application is the processing of high-speed videos of horizontal two-phase stratified and slug flows regimes. Henceforth, in this work, we consider the traditional DMD, the sparsity-promoting DMD (SPDMD) and, in the deep learning context, we select an unsupervised convolutional autoencoder (CAE). In this avenue, it becomes imperative to compare DMD and deep learning with respect to: computational complexity of target techniques; reduced order modeling versus data representation; data set necessary to compute the dynamic modes and deep learning training; the preservation of the phase interface in the DMD and CAE space; data synthesis. In general, the results favor DMD in the considered applications.

Experimental studies of two phase flow characteristics and void fraction predictions in steady state horizontal two-phase nitrogen flow

An experimental characterization of the Two Phase (TP) flow characteristics in a horizontal steady state flow of liquid nitrogen and its subsequent void fraction predictions has been carried out in a novel laboratory set-up. Earlier studies such as that by Jackson et al. (2006) have addressed to such TP characteristics in transient cooling-down scenarios but not in steady state flow regime. Two-phase flow is characterized as per the relative the phase distributions or “flow patterns” or “regimes”. These characteristics have been experimentally investigated in a custom designed laboratory set-up. The flow patterns as a function of externally controlled relative fractions of liquid and gaseous nitrogen have been recorded using a digital imaging device while the temperature and pressure parameters have been recorded with respective sensors. These experiments have revealed the presence of several transitions in the steady state flow of TP nitrogen depending on the initial conditions. The corresponding vapor fractions have been experimentally investigated also. The observed flow regimes have been correlated with standard flow regime maps such as The Backer’s regime map, the regime map given by Taitel and Dukler and The Wojtan flow regime map. The predictions obtained from various flow models are found to be largely converging with the experimental data obtained. These experiments hopefully would lead to future research towards developing prototype void sensor for cryogenic two-phase flows.