Horizontal Annular Flow Research Articles

Measurement of Circumferential Liquid Film in Horizontal Annular Flow Based on PLIF and K-Means Clustering

Measurement of Circumferential Liquid Film in Horizontal Annular Flow Based on PLIF and <i>K</i>-Means Clustering

Experimental and modeling study on liquid film thickness of horizontal gas-liquid annular flow using ultrasonic method

In horizontal annular flow, the high gas velocity leads to the strong randomness, rapidity and complexity of the structure and dynamic characteristics of gas-liquid interfacial wave. As one of the important parameters to describe the interfacial wave, the liquid film thickness is significant to study the hydrodynamic characteristics of the gas-liquid two-phase flow. In this paper, the ultrasonic echo resonance main frequency (UERMF) method and the ultrasonic reference signal elimination (URSE) method are compared by numerical simulation method. The minimum liquid film thickness measured by these two methods are 0.3 mm and 0.01 mm, respectively. Experiments are conducted on a stainless steel test section with an inner diameter of 50.0 mm to study annular air-water flow under five different pressure conditions (from 0.1 MPa to 0.7 MPa). The experimental data is processed using the URSE method to analyze the characteristics of the liquid film under different operating conditions. In addition, based on the aforementioned experimental dataset, a comparison is made regarding the performance of existing predictive correlations. It is found that the existing correlations have certain limitations in capturing the variations of liquid film thickness in annular flow, particularly at high pressures and for different pipe diameters. Therefore, a new liquid film thickness correlation suitable for different system pressures and pipe diameters is proposed. By expanding the range of fitted data points (220 data points), the 95 % relative error of improved model is within ±25 % error band for all available data (authors' and literature). The mean absolute percentage error (MAPE) is 11.08 %. The improved correlation has the applicability and extrapolation for different system pressure and pipe diameter conditions.

Liquid film parameter measurement based on thermal distribution sensor in horizontal annular flow

Liquid film is an important carrier of mass and heat transfer in annular flow, and the parameter detection of which plays an important role in the energy metering of natural gas production processes and the safe and reliable operation of cooling and heating systems. In this paper, a liquid film velocity equation is derived based on the analysis of the heat balance equation between the liquid film and tube wall. According to the constant power principle, the thermal distributed flow measurement sensor is designed by using the multi-physical field coupling simulation technique According to the momentum balance equation of the Laurinat model, considering the pump mechanism of the disturbance wave and using magnitude comparison and stress balance, a liquid film thickness circumferential distribution model in the horizontal annular flow is proposed. Utilizing the model and designed sensor, the liquid film thickness of four locations (0°, 90°, 180°, 270°) measurements are obtained for 64 horizontal annular flow conditions. Laboratory results indicate that the mean absolute percent error of the model is 32.66% and the 82.81% relative error is within the ±30% error band.

An improved model for predicting hydrate formation and deposition in horizontal annular flow

The formation and deposition of hydrates in pipelines form flow barriers, which affect the safety of offshore oil and gas transportation. In this study, an improved model of hydrate formation and deposition is established by considering the non-uniform distribution of liquid film and droplets resulting from gravity, which is a non-negligible factor in the accurate prediction of hydrate deposition in horizontal annular flow. The uneven distributions of the hydrate deposit thickness along the radial and axial directions in a horizontal annular flow were calculated using the proposed model. Three different deposition characteristics of hydrates along the radial direction were found: concave W-type, convex W-type, and Ω-type. Meanwhile, the radial hydrate deposit thickness gradually increased as the gas flow rate increased. With an increase in the liquid flow rate, a greater axial distance between the pipe section and inlet results in a clearer increase in the radial hydrate deposit thickness. In addition, a peak value of the hydrate deposit thickness occurs at a certain position in the axial direction. This study provides a theoretical basis for the prediction and prevention of hydrate blockages during offshore gas transportation.

Simulation of Hydrate Particle Deposition in Horizontal Annular Mist Flow

Summary In the prediction of hydrate deposition, few studies have considered the hydrate particles generated from droplets in the gas core, which makes it difficult to calculate the hydrate particle deposition accurately. Previous studies have introduced the effective deposition ratio (EDR) to predict the hydrate particle deposition from the gas core quantitatively, which simplifies the prediction process. However, a quantitative description of the EDR has not been studied. The current work has established a prediction model of hydrate particle deposition on a pipe wall and developed a method for solving the EDR based on the force analysis and removal mechanism (lifting, rolling, or slipping) of hydrate particles on the horizontal pipe wall in annular mist flow. The effects of gas velocity, pipe diameter, particle size, and other factors on the EDR of hydrate particles were analyzed using the optimized discrete particle model (DPM) in Fluent. The results show that the EDR is inversely proportional to the gas velocity under the comprehensive impacts of the turbulent kinetic energy and gas shear force. Under the influence of the liquid film "wrapping," the EDR rapidly grows and then stabilizes with the increase in particle size. Under the joint influence of the liquid film distribution and forces acting on the particles, the EDR first rapidly declines and then grows with the increase in pipe diameter, and finally tends to be stable. Through regression fitting of more than 700 sets of data, the empirical expression of the EDR of hydrate particles was established for the first time, and the error was within the allowable range in engineering. This work lays a foundation for the accurate calculation of hydrate particle deposition generated from droplets in a gas core.

Horizontal annular flow through orifice studied by X-ray microtomography

An X-ray microtomography (µCT) system was adapted so that 3D scans of fixed horizontal or vertical test sections can be performed. The mobile µCT system has been applied to measure the local, time-averaged volume fraction distribution of developing annular air-water flow in a horizontal pipe with µm spatial resolution. Based on the volume fraction data the liquid film thickness profile is computed and the accumulation, stripping and renewal of the annular liquid film at a circular orifice is studied. The development length of the annular flow downstream of the orifice is evaluated based on the integral volume fraction and the change of the film thickness profile along the pipe axis. Both parameters give a consistent result, indicating that liquid film renewal can be judged based on integral measurement techniques in this case. Further, the detailed 3D data enables the validation of computational fluid dynamics codes based on phase-averaged variables such as the Euler-Euler approach.Graphic abstract

Void fraction measurement using an imaging and phase isolation method in horizontal annular flow

A new imaging method was proposed to measure the void fraction of annular flow based on phase isolation technology in a horizontal circular tube. As the gas–liquid mixture passes through the phase isolation device, which is arranged upstream, a strong swirl flow is created due to centrifugal effect. The liquid phase is pushed to the tube wall and forms a uniform liquid film, while the gas phase is concentrated to the tube center and forms a gas core. This rectified core-annular flow has a more smooth and clear phase interface than that of natural annular flow, which makes the accurate measurement of some inherent flow parameters of gas–liquid two-phase flow possible and much easier to perform. A backlight-collimated illumination and high-resolution CCD camera were employed to capture the gas core and liquid film. A calibration experiment was conducted to acquire an accurate edge detection criterion for recognition of the phase interface. The morphological image characteristics of the core-annular flow and the beam path diagram of imaging procedure were analyzed in detail and a corresponding image processing algorithm was developed. The working fluids were air and water and the ranges of void fraction covered in the sexperiment were 0.736–0.978(Usg = 4.35 m s−1–39.12 m s−1, Usl = 0.016 m s−1–0.504 m s−1). For each experiment condition, about 800 raw images were processed to obtain an average result. Comparisons to a representative model of void fraction of natural annular flow showed that the void fraction of the core-annular flow rectified by the phase isolation device remains well consistent with that of natural annular flow in the range of low-gas volume fraction, while the void fraction of core-annular flow becomes a little lower than that of natural annular flow as the gas volume becomes very high.

Droplet entrainment and deposition rates in a horizontal annular flow for SPACE code

Correlations for the droplet entrainment and deposition rates were developed to accurately predict its behavior in a horizontal annular flow. The Lopez de Bertodano et al. droplet entrainment rate correlation was evaluated and then modified based on the experimental data for both vertical and horizontal annular flows. In addition to this, a new droplet deposition coefficient correlation was proposed for a droplet deposition rate. The droplet deposition coefficient is represented by a function of dimensionless parameters considering the effects of the gas and liquid superficial velocities and the pipe inner diameter. Finally, the SPACE code was assessed against various experimental data for droplet mass flow rate of horizontal annular flows obtained from the open literature. The improved SPACE code showed better prediction capability for the droplet behavior in the horizontal annular flow than the original one.

Condensation Heat Transfer and Pressure Drop of R-404A in 7.0 mm O.D. Smooth and Microfin Tube at Low Mass Fluxes

R-404A condensation heat transfer and pressure drop data are provided for 7.0[Formula: see text]mm O.D. smooth and microfin tubes. Tests were conducted for a range of mass fluxes (from 80 to 200[Formula: see text]kg/m2s) and quality (from 0.2 to 0.8). The heat flux was 6[Formula: see text]kW/m2 and saturation temperature was 45[Formula: see text]C. It was found that both the heat transfer enhancement factor and the pressure drop penalty factor increase as mass flux increases. The range of pressure drop penalty factor (0.99–1.27) was smaller than that of heat transfer enhancement factor (1.21–1.96). Smooth tube heat transfer coefficients and pressure drops are reasonably predicted by Shah [An improved and extended general correlation for heat transfer during condensation in plain tubes, Int. J. HVAC&amp;R Res. 15 (2009) 889–913] and Jung and Radermacher [Prediction of pressure drop during horizontal annular flow boiling of pure and mixed refrigerants, Int. J. Heat Mass Transfer 32 (1989) 2435–2446] correlation, respectively. For the microfin tube, however, all the existing correlations do not adequately predict the present data. Poor predictions may be attributed to the lack of R-404A and low mass flux data in their database.

Experimental investigations of the circumferential liquid film distribution of air-water annular two-phase flow in a horizontal pipe

The circumferential film thickness distribution in an air-water horizontal annular two-phase flow was investigated in 26mm pipe diameter by using the conductance probe. The superficial gas and liquid velocities were 10–40m/s and 0.025–0.4m/s, respectively.In general, the film thickness decreases as the liquid velocity decreases and the gas velocity increases. For low superficial gas velocity, high asymmetry of liquid film thickness distribution is generally found. In addition, the liquid film at the upper half of the pipe mostly consists of surge of waves with frequency lower than that of the bottom. At the lowest superficial liquid velocity of the present experimental range, the mean film thickness at the bottom ranges from 0.24mm to 1.3mm. Meanwhile, at the highest superficial liquid velocity, it ranges from 1.0 to 4.29mm, depending on the superficial gas velocity. At the higher superficial gas velocity, a more uniform of liquid film thickness distribution is commonly found. Under this flow condition, the wave at the upper has a similar frequency to that of the lower half and a coherent liquid wave is normally found.To predict the film thickness at any circumferential position, an empirical correlation is proposed on the basis of the physics of the phenomena. In comparison to the available experimental data, the correlation has a good capability to predict the circumferential liquid film thickness distribution.

Asymmetry during a horizontal annular flow in a micro-channel: optical measurements and effect of dimensionless numbers

New applications of HFC refrigerants in organic Rankine cycles at high saturation temperatures and the wider use of CO2 for air-conditioning have pushed research to the characterization of two-phase heat transfer at medium/high reduced pressures and have pointed out the effect of these operating conditions on asymmetric distribution of refrigerant around tube perimeter and its indirect effect on heat transfer. Currently there is a lack of data about asymmetric distribution of liquid film at the wall, especially for refrigerants and micro-channels. In order to have a physical evidence of this asymmetry also for micro-channels and approach to a relationship between this phenomenon and dimensionless parameters, new data are here presented. The asymmetric annular flow of the refrigerant R245fa inside a horizontal, round 2.95 mm inner diameter channel is studied with pictures captured by a high speed video camera. The experimental results here presented were obtained at saturation temperatures equal to 20 °C and 40 °C at low mass velocities (50, 100 and 200 kg m-2s-1) to asymmetric distribution, enriching the database presented in previous studies. The new dimensionless parameter, eccentricity, has been related to the dimensionless groups: Froude and Bond numbers, and Martinelli parameter, showing the mutual correlation among them.

Effects of Surface Tension on the Liquid Holdup and Wave Characteristics in Horizontal Annular Two-Phase Flow

The wave characteristics of horizontal annular two-phase flow in 16 mm diameter pipe were experimentally investigated using flush-mounted constant electric current method (CECM) sensors and visual observations. To examine the effect of surface tension on the wave velocity and frequency, air and three kinds of liquids with different surface tension were used, i.e., water, 2%-butanol solution, and 5%-butanol solution. The gas and liquid superficial velocities were varied from 12 to 40 m/s and 0.05 to 0.2 m/s, respectively. The liquid holdup was measured directly using CECM, while the wave velocity and frequency were determined using cross correlation and power spectral density functions of liquid holdup signals. Generally, combination of air and liquid with the highest surface tension gives the highest liquid holdup and wave frequency. Simple correlations for wave velocity and wave frequency were also developed.

Effects of Liquid Viscosity on the Wave Velocity and Wave Frequency in Horizontal Annular Flow

An investigation on the liquid holdup, wave velocity, and wave frequency in horizontal annular flow has been experimentally conducted through the measurement of liquid holdup using constant electric current method (CECM) sensors. To investigate the effect of viscosity, water and glycerin were used as working liquid, using superficial liquid velocity and superficial gas velocity of 0.05 to 0.2 m/s and 12 to 40 m/s, respectively. Liquids with higher viscosity give the higher liquid holdup, lower wave velocity, and lower wave frequency. Correlations for liquid holdup and mean film thickness, wave velocity, and wave frequency have been developed with mean average errors (MAE) of 13.5%, 9.2%, and 8.6%, respectively.

Numerical modeling of a horizontal annular flow experiment using a droplet entrainment model

One limitation in current simulating horizontal annular flows is the lack of treatment of droplet formation mechanisms. For self-generating annular flows in horizontal pipes, the interfacial momentum exchange and the turbulence parameters have to be modelled correctly. Furthermore the understanding of the mechanism of droplet entrainment in annular flow regimes for heat and mass transfer processes is of great importance in the chemical and nuclear industry.A new entrainment model is proposed. It assumes that due to liquid turbulence the interface gets rough and wavy and forms droplets. The new approach is validated with HZDR annular flow experiments. Important phenomena like the pressure drop, the wave pumping effect, the droplet entrainment, the liquid film formation and the transient flow behavior could be calculated, analyzed and some of the phenomena compared with the measurement.

Experimental Investigation on Disturbance Wave Velocity and Frequency in Air-Water Horizontal Annular Flow

The wave characteristics of horizontal air-water annular two-phase flow in 16 and 26-mm-diameter pipe were investigated experimentally using flush-mounted constant electric current method (CECM) sensors and visual observations. The air and water superficial velocities were varied from 12 to 40 m/s and 0.05 to 0.2 m/s, respectively. The flow morphology of annular flow such as the disturbance wave, ripple, wave coalescence, wave development, entrainment, and breakup could be observed. Using cross correlation and power spectral density functions of liquid holdup signals, the wave velocity and frequency were determined. The effect of superficial liquid velocity on the wave velocity and frequency was found to be less significant compared to that of superficial gas velocity. Simple correlations for wave velocity and frequency were also developed.

A simple model for predicting the pressure drop and film thickness of non-Newtonian annular flows in horizontal pipes

A model of two-phase non-Newtonian horizontal annular flows, which predicts film thickness and pressure gradient from flowrates only, is presented. In the model, the gas and non-Newtonian liquid flows are calculated separately based on the independent governing equations. The shear stress balance at the gas–liquid interface is calculated in order to link two phases together. The non-Newtonian fluid is assumed as a power-law shear-thinning liquid. The logarithmic velocity distribution is chosen to calculate the turbulent velocity profile in the gas core. The influences of entrainment and aeration are included in the model. The pressure drop, film thickness, void fraction, the frictional multiplier, and Lockhart–Martinelli parameter are predicted. The analytical model is compared with the published experimental investigations, and the results show that the model can predict the film thickness and pressure gradient simultaneously based on the flowrates of liquid and gas. The frictional multiplier and Lockhart–Martinelli parameter are calculated at the same time, and the predicted values are comparable with the experimental data. The difference between the analytical model and the experiments is lower than 10%.

Liquid film circumferential asymmetry prediction in horizontal annular two-phase flow

This study considers the prediction of the degree of asymmetry in the circumferential distribution of the liquid film in the tube cross section of horizontal annular gas–liquid two-phase flow, endemic of the lower region of this flow regime near the stratified-wavy flow transition boundary. Focusing on disturbance waves as the predominant mechanism for transporting the liquid in the annular film from the bottom to the top of the tube to counterbalance the draining effect of gravity, a new prediction method for the degree of asymmetry in the annular liquid film is proposed that outperforms existing correlations. Flow pattern maps for horizontal gas–liquid two-phase flow of frequent use in the design of evaporators and condensers can thus be explicitly updated to account for both symmetric and asymmetric annular flows. The underlying experimental database contains 184 measured liquid film circumferential profiles, corresponding to 1276 local liquid film thickness measurements collected from 15 different literature studies for tube diameters from 8.15mm to 95.3mm.

Liquid Entrainment in Annular Gas/Liquid Flow in Inclined Pipes

Summary Entrainment fraction is one of the key parameters in many applications, including wellbore and flowline design, separator design, wellbore loading, and corrosion inhibition. This study provides the first comprehensive entrainment data and their critical analysis for a full range of inclination angles ranging from horizontal to vertical in 76.2-mm-internal-diameter (ID) pipes. Experiments were conducted to investigate the effect of pipe inclination on entrainment fraction in air/water annular flow with inclination angles of 0, 10, 20, 45, 60, 75, and 90° from horizontal. Two techniques were used to measure the entrainment fraction: film removal and isokinetic sampling. The experimental results were compared with existing models and correlations, and the best predicting methods were determined for all flow orientations. An inclination effect on entrainment fraction was observed. This effect occurred at low superficial gas velocities and was more prominent for higher superficial liquid velocities. Using the present study data, the Paleev and Filipovich (1966) correlation was found to be the most accurate in predicting entrainment fraction. On the basis of all available data, the Pan and Hanratty (2002b) correlation performed the best in predicting entrainment fraction in all pipe orientations. For vertical annular flow, the Oliemans et al. (1986) correlation predicted entrainment fraction more accurately. The Pan and Hanratty (2002b) correlation was the most accurate in predicting entrainment fraction for horizontal annular flow. The Wallis (1969) correlation and the mechanistic model developed by Mantilla (2008) most accurately predicted the entrainment fraction for inclined annular flow.

Liquid film characterization in horizontal, annular, two-phase, gas–liquid flow using time-resolved laser-induced fluorescence

A non-intrusive optical technique was developed to provide time-resolved longitudinal and cross-sectional images of the liquid film in horizontal annular pipe flow of air and water, revealing the interfacial wave behavior. Quantitative information on the liquid film dynamics was extracted from the time-resolved images. The planar laser-induced fluorescence technique was utilized to allow for optical separation of the light emitted by the film from that scattered by the air–water interface. The visualization test section was fabricated from a tube presenting nearly the same refractive index as water, which allowed the visualization of the liquid film at regions very close to the pipe wall. Longitudinal images of the liquid film were captured using a high-frame-rate digital video camera synchronized with a high-repetition-rate laser. An image processing algorithm was developed to automatically detect the position of the air–water interface in each image frame. The thickness of the liquid film was measured at two axial stations in each processed image frame, providing time history records of the film thickness at two different positions. Wave frequency information was obtained by analyzing the time-dependent signals of film thickness for each of the two axial positions recorded. Wave velocities were measured by cross-correlating the amplitude signals from the two axial positions. For the film cross-section observations, two high-speed digital video cameras were used in a stereoscopic arrangement. Comparisons with results from different techniques available in literature indicate that the technique developed presents equivalent accuracy in measuring the liquid film properties. Time-resolved images of longitudinal and cross-section views of the film were recorded, which constitute valuable information provided by the technique implemented.

Freezing technique for measuring and predicting the size of droplets in a horizontal annular flow

Abstract A freezing technique for measuring the size of droplets was developed to obtain the droplet size distribution in a horizontal annular flow in a pipe with a 37.1 mm diameter. Droplets are frozen by using an extremely low temperature nitrogen gas with liquid film extraction. They are then photographed with a microscope and a CCD camera and measured by means of an image process. The results are compared with various experimental data. The droplet sizes measured by the freezing technique are comparable with those measured by other methods at a high air superficial velocity (of 50 m/s). However, because of the film extraction problem, the droplet sizes measured at a low air superficial velocity of less than 40 m/s are higher than those measured by other methods. A suggested method of predicting the Sauter mean diameter is based on the maximum droplet size correlation for the experimental data, with and without liquid film extraction. The average droplet size is remarkably smaller downstream of the liquid film extractor because large droplets from the liquid film are excluded.