Phase Flow Patterns Research Articles

Pore-scale study of the effects of surface roughness on relative permeability of rock fractures using lattice Boltzmann method

Two-phase flow in fractured geo-material plays a significant role in various subsurface processes. Despite some success in studying two-phase flow in ideal smooth-walled fractures, the more realistic issues regarding two-phase flow in rough-walled fractures are still not well understood. In this study, an improved approach based on free energy lattice Boltzmann model is proposed to analyze the two-phase immiscible flow in the rough-walled fracture and to further estimate the relative permeability curves. The proposed model is validated by comparison with analytical results of individual fracture, and good agreement is achieved in general. Then it is used to investigate the effects of wall roughness and the initial phase distribution patterns on the co-current flow of two immiscible fluids. The simulation results demonstrate that roughness impacts phase distribution, flow patterns and relative permeability curves in a single rough-walled fracture. Rough surface increases two-phase interference and flow resistance, and an unsteady flow state appears for the non-wetting phase (NWP) when the wetting phase (WP) saturation is small. In addition, the NWP flow can either be lubricated or be resisted by the WP depending on the flow patterns and the WP saturation.

소수성 미니채널 내 물-에탄올 혼합 액적 슬러그 거동에 따른 접촉선에서의 압력강하에 대한 실험적 연구

At a two phase flow, according to gas and liquid phase flow rates, various flow regimes are developed such as bubbly, slug/plug, churn, annular, droplet flow and so on. At a two phase flow in small scaled channels, among various flow regimes, the intermittent flows such as bubbly, slug/plug flow are developed in the broad regions of two phase flow pattern map. In particular, the flow regimes are influenced by surface wettability. In a case of slug flow in hydrophobic small scaled channels, gas and liquid phases are perfectively separated by interfaces and contact line. The pressure drop of the two-phase flow is largely generated at moving contact line. Therefore, to well design two-phase flow system with small scales, it is important to estimate the pressure drop at moving contact line. In this study, on the basis of previous research, the pressure drop at moving contact line is experimentally measured for a various fluids (0-40% water-ethanol mixtures). And, the previous correlation to estimate pressure drop at moving contact line is verified by experimental data. In an addition, we discuss interfacial broken phenomena of slug flow in a minichannel. (D=1.555mm).

Modeling of the Process in a Packed Fractionating Column with Diffusive Liquid Phase Flow Pattern

Working line and mass transfer equations are derived analytically for rectifying and stripping sections of a packed fractionating column with a diffusive continuous liquid phase flow pattern. A calculation algorithm is proposed and the obtained process and geometric parameters are compared with the same parameters of the same column calculated by the standard algorithm, taking account of the fact that the disperse gas phase has an ideal-displacement flow pattern and the continuous liquid phase has an ideal-mixing flow pattern.

Dynamic Modeling of Two-Phase Gas/Liquid Flow in Pipelines

Summary Presented is a reduced–order thermal fluid dynamic model for gas/liquid two–phase flow in pipelines. Specifically, a two–phase–flow thermal model is coupled with a two–phase–flow hydraulics model to estimate the gas and liquid properties at each pressure and temperature condition. The proposed thermal model estimates the heat–transfer coefficient for different flow patterns observed in two–phase flow. For distributed flows, where the two phases are well–mixed, a weight–based averaging is used to estimate the equivalent fluid thermal properties and the overall heat–transfer coefficient. Conversely, for segregated flows, where the two phases are separated by a distinct interface, the overall heat–transfer coefficient is dependent on the liquid holdup and pressure drop estimated by the fluid model. Intermittent flows are considered as a combination of distributed and segregated flow. The integrated model is developed by dividing the pipeline into segments. Equivalent fluid properties are identified for each segment to schedule the coefficients of a modal approximation of the transient single–phase–flow pipeline–distributed–parameter model to obtain dynamic pressure and flow rate, which are used to estimate the transient temperature response. The resulting model enables a computationally efficient estimation of the pipeline–mixture pressure, temperature, two–phase–flow pattern, and liquid holdup. Such a model has utility for flow–assurance studies and real–time flow–condition monitoring. A sensitivity analysis is presented to estimate the effect of model parameters on the pipeline–mixture dynamic response. The model predictions of mixture pressure and temperature are compared with an experimental data set and OLGA (2014) simulations to assess model accuracy.

A new diabatic two phase flow pattern transition model of R600a

In this paper, a detailed experimental study was carried out to investigate the two phase flow patterns of R600a in a smooth horizontal tube with an inner diameter of 6 mm. The experiments were performed at conditions covering saturation pressures from 0.215 to 0.415 MPa, mass fluxes from 67 to 194 kg m−2 s−1 and heat fluxes from 10.6 to 75.0 kW m−2. Based on high speed camera, four main flow regimes can be identified: plug flow, stratified-wavy flow, slug flow and annular flow. Intermittent flow (include plug and slug flow) to annular flow transition was detected and plotted on flow pattern map. Comparisons between available intermittent/annular (I/A) transition lines in the literature and the experimental data have been made. The result shows that no transition equations can fit the experimental transition curve well. By taking the surface tension, gravity force, heat flux, viscosity and density into account, four dimensionless number were introduced into the transition equation. Finally, a transition equation of intermittent/annular flow for R600a was proposed and shows good agreements with the experimental data.

Phenomenological correlations for two phase heat transfer and pressure drop performance of electrohydrodynamic horizontal convective boiling of dielectric fluids

EHD is an active heat transfer enhancement technique for convective boiling or condensing dielectric fluids whose performance varies widely in the literature for even the same geometry and fluids. As such, the performance of EHD convective boiling devices remains largely unpredictable. Two empirical EHD convective boiling heat transfer coefficient correlations exist in the literature with good performance when compared to their exact test dataset and geometry, however they have been shown to have poor correlations in predicting the performance for external test datasets. In this paper, a phenomenological approach is taken in the development of a new EHD convective boiling heat transfer coefficient correlation and a novel EHD convective boiling pressure drop correlation. The performance correlations are based on widely-used free-field convective boiling correlations for heat transfer coefficient and pressure drop with phenomenological enhancement factors based on the two phase flow pattern as predicted using the EHD two phase flow pattern map which accounts for the effect of electric field strength on flow pattern redistribution, as described in a previously published paper (Nangle-Smith and Cotton, 2018). A review of the EHD convective boiling experimental literature was conducted to determine confounding factors that can impact the large variance in the reported performance. Flow pattern and applied heat flux were identified as common parameters not maintained constant in the experimental data. Two datasets, including data from the present study, in which flow pattern and applied heat flux are maintained constant were used in the development of the performance correlations. Considerable improvement over previous EHD convective boiling performance correlations was found both in error and the physical significance of coefficients. The correlations were developed for thermodynamic qualities in the range of 20–60% below the onset of dryout or mist flow patterns and for applied heat fluxes < 30 kW/m2. Furthermore, test conditions in this study were chosen to focus on the dielectrophoretic effect and therefore studies with significant electrophoresis were not included. Thus, the correlation is limited to positive applied voltages, saturated flow boiling conditions, and field strengths below the onset of charge injection. The authors recommend this approach for EHD two phase performance correlation development as it is more mechanistic, is analogous to the state-of-the-art approaches for free-field two phase performance, and is likely to yield more accurate models as more experimental data becomes available.

Characteristics of liquid flow in a countercurrent rotating bed

A rotating packed bed (RPB) is a new type of process intensification equipment. Its packing zone is an important mass transfer zone. However, the issue of liquid flow in the RPB remains unclear. In this work, the effects of rotational speed, liquid initial velocity in the cavity, and the packing zone of a countercurrent rotating bed on liquid phase flow patterns, droplet velocity, average droplet diameter, and droplet size distribution were measured using a charge-coupled device (CCD) camera in the air–water system. Experimental results show the influence of rotational speed and liquid initial velocity on fluid flow characteristics. Computational fluid dynamics modeling was employed to analyze the characteristics of liquid flow. Two-dimensional numerical simulation of gas–liquid two-phase flow was achieved using the volume of fluid model in the multiphase flow model and the Reynolds stress model in the turbulence model. Simulation results are consistent with the experimental rules. In addition, correlations were established to predict the average droplet diameter, the rotational speed, and the liquid initial velocity. The predicted values were in agreement with the experimental values, with deviations generally within ±15%.

Development of an annular mist flow generating device for air-water flow

Annular mist flow generating device is being developed to generate annular mist flow of air and water to simulate two phase flow pattern in the evaporator. The annular mist flow generating device is use for experimental study of the air water flow behaviour that simulates the two phase flow of refrigerant. Annular mist flow at inlet of the dividing header will provide batter air water distribution to the branches. The annular mist flow generating device shall be designed using computer aided drawing (CAD) software. Then, fabricate the annular mist flow generating device. After that, the annular mist flow generating device will be test experimentally by visual observation of the air water flow pattern. The air superficial velocity and water superficial velocity use in this experiment is 1.0m/s - 5.0m/s and 0.015m/s - 0.045m/s respectively. The test channel had a horizontal header with a square cross section of 20mm × 20mm and length of 290 mm with 10 upward branches. In this experiment the air water flow patterns is observed and recorded using digital camera. It was found that the device generate annular mist flow at frontal of the dividing header. This experiment proved that the device is capable of generating annular mist flow within the design range of air and water superficial velocities.

A mechanistic approach to developing two phase flow pattern transition maps for two-phase dielectric fluids subject to high voltage polarization

High voltage electric fields can be used as an active heat transfer enhancement technique for convective boiling or condensing dielectric fluids, with the major component of this enhancement being attributed to phase redistribution and mixing in the system due to electric body forces. Many performance prediction tools for convective boiling and condensation rely on flow pattern maps to identify the flow regime for use with flow pattern specific heat transfer and pressure drop correlations [1,2]. In this paper, a mechanistic approach to developing two phase flow pattern maps for two-phase dielectric fluids subject to high voltage fields using a fully contained, equation-based electric Froude number approach is presented and compared against the experimental flow pattern data for EHD convective boiling & condensation available in the literature and from the current experimental study. Despite the development of newer diabatic, semi-mechanistic flow pattern models for free-field heat exchanger performance analysis, it is recommended that the Steiner equations for flow pattern transition be used as a basis for the mapping when additional physics such as EHD is coupled, as the empirical fits in newer semi-mechanistic maps are unreliable when additional physics is present.

Mini-channel Two Phase Flow of Hydrogen Peroxide: Decomposition with Silver Catalyst

Hydrogen peroxide is a chemical compound which is commonly used as a disinfectant at lower concentrations. The chemical is called as a green propellant for space applications. Water and oxygen are the products after self-decomposition of the compound at higher concentrations. The reaction rate at lower concentrations can be enhanced by using catalysts for faster reaction rates. In the present study, an experimental analysis of the reaction rate of hydrogen peroxide (6% by volume) with silver catalyst for varying flow rates is detailed. Reaction takes place in a long cylindrical borosilicate glass tube of diameter 2.50 mm. Separation of product mixture takes place in an enlarged tube of diameter 5.50 mm. Various two phase flow patterns formed after decomposition reactions are identified by images captured using high speed camera. Length of oxygen slug formed after catalytic reaction is measured by employing Image processing techniques.

A note on using VOF method for polymer bead manufacturing

The production of mono-dispersed spherical and non-spherical polymer beads and capsules using micro-fluidics requires precise control of dispersed phase which are distributed in a continuous phase. The prediction of two phase or three phase flow patterns in the mini/micro channels finds its application in production process of such spherical polymers. In the present work a numerical model based flow analysis is done for creation of the spherical/non spherical dispersed air bubbles in a continuous liquid phase. The results are validated with experiments done in a similar liquid–gas flow experiments carried out in a glass mini channel of size 2.05 mm. The flow regime is recorded with a high speed camera. The volume of fluid model in ANSYS Fluent software is used to predict the flow pattern details numerically. The model can be effectively used for predicting the size behavior in such spherical/non-spherical polymer bead production.

Interrogating flow development and phase distribution in vertical and horizontal pipes using advanced instrumentation

The characterization of two-phase flow in both vertical and horizontal pipes is important in oil/gas transportation. As the pipe orientation may change from well to well, it is also important to understand the characteristic responses expected of a two-phase mixture to a change in pipe inclination. This study concerns the changes in the void fraction, structure frequency and structure velocity that occur within an air–silicone oil mixture as a function of the pipe orientation. Experimental data were obtained from the combined use of electrical capacitance tomography (ECT) and wire mesh sensors (WMS), which allow the 3D visualization of the flow patterns. The reported experiments were performed on a 67 mm diameter pipe, in a flow loop, in which a pipe section may be inclined at angles of between −5 or 90° to the horizontal. For this study, the inclined pipe was either set at an angle of 0 or 90 to the horizontal, which correspond to a horizontal or vertical pipe setting, respectively. The results of flow development using the PDF of void fraction obtained at 3 measurement locations; ECT 1, ECT 2 and WMS at 4.4, 4.489 and 4.92 m, respectively, showed that the flow is fully developed and statistically stable for the vertical two-phase flow. While on the other hand, the flow is in rapid development for the horizontal two-phase flow scenario at same liquid and gas superficial velocities. The processed data reveal the differences in flow distribution produced by the pipe inclination. Within the vertical pipe configuration spherical cap bubbles, slug and churn two phase flow patterns were observed, whilst plug, slug and stratified wavy two-phase flows were identified in the horizontal configuration of the pipe. It is concluded that a plot of mixture superficial velocity against average void fraction may be used to provide a qualitative assessment of the flow patterns observed, regardless of pipe inclination. The two-phase flow variables that are concluded to significantly influence the distribution coefficient, C0, and drift velocity, VD, are the pipe orientation and flow patterns.

Analysis of Two-Phase Flow Pattern Identification Methodologies for Embedded Systems

The Main goal of Two Phase Flow Pattern Identification is to pinpoint the correct pattern in terms of flow in a given section of a pipe. The identification of these patterns has applications in several areas, such as chemical and oil industries. When technologies of identification in real systems are intended to be used, several aspects must be considered, such as data size, memory, processing power. The objective of this paper is to investigate the possibility of embedding a methodology to identify flow patterns in devices that have limited processing power and memory capacity. In this sense, several statistical operations were made aiming to reduce the information needed to identify the patterns. Tests were conducted simulating reductions in data size, resulting in no loss quality at the identification process. From tests performed, it was discovery an efficient identification model and computationally easy to be embedded in a small devices.

Two Phase Flow Pattern of Injection Lubrication in High Speed Bearings

In this paper, the study of Numerical analysis of bearing lubrication flow field is presented. When the lubricating oil flows into the bearing, the fluid distribution in the radial direction assumes a gradient state under the influence of the centrifugal force at high speed. Through the experiment, it is recommended to be more than the angle of 450 of the nozzle lubrication. With variable contact radius, the fluid gathered more concentrated, which is not conducive to the rolling lubrication and cooling. When R arc of contactor is not 0mm, the contact wear section is shown the horizontal elliptical shape, and as the radius decreases, the elliptical axis increases, and more requirements of bearing lubrication conditions in this case.

Analysis of the characteristics of two-phase flow pattern in Y-shape mixed microchannel based on double coupled Duffing vibration simulation detection system

In this work, a visualization experiments were carried out in the Y-shape mixed rectangular microchannels with the hydraulic diameter of 133 μm at atmospheric pressure and at room temperature (25 °C). In the experiment, the range of inlet gas superficial velocities was 0.01–16.668 m/s, and the inlet liquid superficial velocity was 0.01–6.945 m/s. The main flow patterns observed in the experiments were slug flow, elongated slug flow, slug-annular transition flow, annular flow. Flow pattern maps were drawn according to the experimental data. Unlike the traditional friction resistance based rationalization for two phase flow patterns, this study relates the two-phase flow pattern mainly to the surface wettability of the material, the shape of the cross section and the hydraulic diameter of the microchannel. The new correlation presents the flow pattern transition boundary according to these three factors. In addition, the coupled Duffing vibration simulation system method is presented as a way to detect signals determining gas-liquid two-phase flow patterns and to analyze the flow characteristics. Based on the instantaneous oscillator velocity and displacement, we can deduce the underlying dynamics of two-phase flow patterns. The Duffing detection method can serve as a model for other nonlinear system analysis and other multi-phase flow characteristics analyses.

Numerical simulation of vortex-induced vibration of a circular cylinder with different surface roughnesses

The effects of surface roughness on the vortex-induced vibration (VIV) performances of a circular cylinder were studied numerically. The VIV response amplitude, response frequency, vortex force, vortex phase and vortex shedding flow pattern with different degrees of surface roughness were compared. The numerical results show that the VIV response amplitude decreases with increased surface roughness. For a smooth cylinder and a cylinder with small surface roughness, the VIV response could be divided into three branches: initial branch, upper branch and lower branch. In the initial and upper branches, the vortex shedding flow pattern displays a 2S mode. However, the VIV response produces a 2P mode vortex shedding pattern in the lower branch. For a cylinder with large surface roughness, the VIV response can be divided into only two branches: an initial branch and a lower branch. In the initial branch, the vortex shedding flow pattern displays a 2S mode, but in the lower branch, the pattern changes to the 2P mode. The transition of 2S mode to 2P mode is caused by the abrupt change of the vortex phase between the vortex force and the VIV response.

Experiment investigation of two-phase flow pattern transition and frictional pressure drop of R600a in a horizontal tube

With the growing concern of environment problems, there are urgent demands for environment-friendly refrigerants in the refrigeration industry. As a natural refrigerant, R600a not only has zero ozone depletion potential and quite low global warming potential, but also has better cooling performance than other refrigerants. Due to its good cooling performance and environment-friendly characteristics, R600a has been used as an alternative refrigerant in heat transfer applications such as refrigerators, freezers, and heat pumps. It is known that accurate prediction of two phase flow pattern transition and frictional pressure drop of R600a in a horizontal tube play an important role in design and optimization of refrigerators, freezers, and heat pumps. According to this issue, a detailed experimental study was carried out to investigate the two-phase flow pattern transition and frictional pressure drop characteristics of R600a in a smooth horizontal tube with an inner diameter of 6 mm. The experiments were performed at conditions covering saturation temperature from 282.4 to 304 K, mass fluxes from 67 to 194 kg/(m2 s). Based on a high speed camera, four main flow regimes can be observed: plug flow, stratified-wavy flow, slug flow and annular flow. The flow map of R600a has been drawn and comparisons between the experimental data of flow patterns and transition lines in the literature have been made. The results showed that with the increase of mass flux, the inception of the annular flow regime occurs earlier. The intermittent flow regime takes place over a narrow range of vapor quality and annular flow regime occupies a wide range of vapor quality. In addition, the trend of Barbieri and Ong and Thome I / A transitions lines are consistent with the experimental data. However, both of them overestimate the inception of the annular flow regime. After taking the influence of vapor inertia, liquid viscous and surface tension forces into account, a modified Weber number We * has been introduced to the new flow pattern transition model. Based on the relationship of X tt and We *, a new correlation has been proposed and it can well fit with the experimental data of flow pattern. Furthermore, a detailed discuss of frictional pressure drop of annular flow and non-annular flow has been made. The results indicated that frictional pressure drop increases with the increases of vapor quality. The tendency of frictional pressure drop presents different the changing laws in different flow regime. The frictional pressure drop increases slowly in the non-annular flow regime while it increases rapidly when the flow pattern turns into the annular flow regime. The reason is that the vapor-phase pressure drop often dominates the total two-phase frictional pressure drop. The annular flow regime owns higher void fraction than the non-annular flow regime. Nine classic prediction correlations of pressure drop were evaluated and the results showed that the correlation of Gronnerud and Muller-Steinhagen and Heck give the best fit to the experimental frictional pressure drop of annular flow and non-annular flow with a mean absolute relative deviation of 38.5% and 19.7% respectively.

Phase separation and flow pattern modulation with a T-type micro-drainage system

T-junction is a classical structure for the two-phase separation. The analysis of gas-liquid flow and the interface movement at the T-junction is very important to the mechanism understanding especially for T-micro-junctions with unequal diameter joint. A simulation of the passive draining process and the corresponding flow pattern modulation of slug flow in a tube with three T-micro-junctions are presented in this paper. Using the volume of fluid (VOF) method and the dynamic grid adaption method the interface movement was tracked precisely especially at the region of drainage junctions. As results, with the separation of liquid no apparent change of gas slugs’ length but shortened water plugs. The gas fraction in main tube is increased more than 10%. During the separation process, the interface movement at unequal diameter junctions mainly consisted of three stages: the generation of penetrating bubbles, a stable sliding stage and the retraction to mother bubble. These constitute one piston movement of penetrating bubbles, which is the vital mechanism of phase separation. The cooperation of interface pressure difference, surface tension, interphase shear force and characteristic sizes of micro-channel drainages brings into a separation. A preliminary model to optimize characteristic sizes of porous materials is proposed in order to getting a successful liquid separation from a slug flow, which could improve the condensation heat transfer performance.

Two-phase flow patterns for condensation of ethanol-water mixtures in triangular microchannels

An array of isosceles triangular microchannels with sidewalls inclined at 54.7° were fabricated by the wet etching method. The condensation of water and ethanol binary mixtures was visualized with additional measurements to investigate the condensation flow patterns in the silicon microchannels with hydraulic diameters of approximately 155μm. The visualization study indicated that the flow patterns were influenced by the inlet ethanol concentration and the mass flux. Annular, injection, droplet-injection and bubble flow patterns were observed along the channels. The condensation instability effects were stronger with increased equivalent surface free energy differences. The increasing equivalent surface free energy differences caused droplets to form in the microchannel that moved from the condensing surface to the top corner due to the Marangoni effect, which led to fluctuating flow patterns. The frequency of the injection flow increased with increasing Rev and input ethanol concentration. The mass flux and the steam quality during condensation were measured at various locations in the experiments. Two phase flow pattern maps were developed for various inlet ethanol concentrations.

Experimental study of full field riser hydrodynamics by PIV/DIA coupling

A full-field hydrodynamic study under riser flow conditions is performed, by using a combined Particle Image Velocimetry (PIV) and Digital Image Analysis (DIA) technique. The employment of a temporal histogram-based method (THM) enables an accurate measurement of the solids volume fraction over the full field of a pseudo-2D riser unit. The full visual access to the riser section enables a complete characterization of the complex transient particulate phase flow patterns. Full-field riser hydrodynamics are quantified at different operating conditions defined by the superficial gas velocity. Under these conditions, a cluster detection method is utilized to characterize the heterogeneity of the riser flow.