Water Superficial Velocities Research Articles

Precise Evaluation of Gas–Liquid Two-Phase Flow Pattern in a Narrow Rectangular Channel with Stereology Method

The drive to increase the efficiency of processes based on two-phase flow demands the better precision and selection of boundary conditions in the process’ control. The two-phase flow pattern affects the phenomena of momentum, heat, and mass transfer. It becomes necessary to shift from its qualitative to quantitative evaluation. The description of the stationary structure has long been used in structural studies applied to metals and alloys. The description of a gas–liquid two-phase mixture is difficult because it changes in time and space. This paper presents a study of the precise determination of two-phase flow patterns based on stereological parameters analysis. The research area is shown against the flow map proposed by other researchers. The experiment was taken in the thin clear channel with dimensions of W = 50 × H = 1200 × T = 5 mm. The test method is based on the visualization of a two-phase air–water adiabatic flow pattern in the rectangular channel where superficial air velocities ranging from 0.006 to 0.044 m/s and the superficial water velocity ranged from 0.011 to 1.111 m/s. A high-speed camera was used for visualization. Images were analyzed with the use of stereological techniques. The study included the classification of structures according to generally accepted two-phase flow regime nomenclature for upwards co-current gas–liquid flow in a vertical rectangular channel. The result of the research was the determination of the stereological parameters’ changes with reference to the two-phase mixture flow hydrodynamics. The results were presented as waveform fluctuations in the values of stereological factors such as the volume fraction VV, interfacial surface SV, number of objects NV, mean chord l′m and the free distance λ. The description of how these parameters change with changes in phase fluxes is also presented. These waveforms help to distinguish the transient flow regimes, which allow for the automatic adjustment of the process stability. The authors found templates of the stereological parameters’ dependencies for flow pattern recognition. The research demonstrates wide possibilities of stereological methods’ application for the analysis of the two-phase gas–liquid process. The stereological model of two-phase pattern control enables the identification of process disorders.

Research on hydrodynamics of high velocity regions in a water-jet pump based on experimental and numerical calculations at different cavitation conditions

Cavitation is a common phenomenon and continues to be a primary concern in the fields of hydraulic machinery. To provide a reference for cavitation flow and cavitation performance improvement, this paper presents the experimental study on the cavitation flow structures of the water-jet pump. High-speed photography technology is used to capture the cavitation flow structures and reveal the physical process of cavitation evolution in the water-jet pump. Cavitation–vortex interaction was further explored by numerical simulations. By extracting 24 m/s water velocity isosurface and analyzing the water superficial velocity on the isosurface, the flow characteristics in the high-velocity fluid area under different cavitation stages are revealed. Then, by analyzing the vortex structure on the isosurface, the main factors affecting the development of the vortex structure on the high-velocity fluid area are summarized.

Experimental Analysis of Water/Oil Displacement Tests in Horizontal Pipe

Summary Production shutdowns occur often throughout the life cycle of an oil field. In offshore fields, shutdown situations are accompanied by an intense heat exchange between pipeline and cold water, which exponentially increases oil viscosity. Such an event may lead to serious difficulty to restart the production, or even render it unfeasible, especially for heavy oil fields. Therefore, a preventive procedure is required to remove the ultraviscous oil from pipelines and risers; for example, by pumping diesel or methanol in a flush procedure. Designing an efficient cleanup procedure is therefore essential in terms of time, amount of fluid injected, and pumping system requirements. However, the amount of research published in this area is limited. In this paper, we propose a comprehensive analysis on how the displacement of a viscous liquid by a less-viscous liquid occurs in a pipeline through footages in different segments, varying the injection velocity. Two mineral oils with different viscosities and tap water were used as working fluids for this study. The experimental setup was built with a horizontal 10-m-long acrylic pipe with 19-mm internal diameter. Two high-speed cameras were placed both in the inlet and outlet segments. Our results demonstrate how water displaces viscous oil in a pipeline, showing different flow configurations as superficial water velocity increases, depending on the oil viscosity and distance from the inlet. A dimensionless analysis was performed by a combination of the forces that govern the flow and dimensionless groups found in literature. The results show an expected area of optimum values regarding cleaning time according to flow configuration. A unidimensional model using a logistic function was proposed and showed a good agreement with the experimental data. The model itself proven to be an easy tool for industry and academic purposes, supporting even more robust and elaborated models in the future.

Flow pattern and pressure drop for oil\u2013water flows in and around 180\xb0 bends

Pressure drop and flow pattern of oil–water flows were investigated in a 19-mm ID clear polyvinyl chloride pipe consisting of U-bend with radius of curvature of 100 mm. The range for oil and water superficial velocities tested was 0.04 le U_{{{text{so}}}} le 0.950 ;{text{m/s}} and 0.13 le U_{{{text{sw}}}} le 1.10 ;{text{m/s}}, respectively. Measurements were carried out under different flow conditions in a test section that consisted of four different parts: upstream of the bend, at the bend and at two redeveloping flow locations after the bend. The result indicated that the bend had limited influence on downstream flow patterns. However, the shear forces imposed by the bend caused some shift flow pattern transition and bubble characteristics in the redeveloping flow section after the bend relative to develop flow before the bend. Generally, pressure gradient at all the test sections increased with both oil fraction and water superficial velocity and there was a sharp change of pressure gradient profile during phase inversion. The transition point where phase inversion occurred was always within the range of 0.4 le U_{{{text{sw}}}} le 0.54 ;{text{m/s}}. Pressure losses differed at the various test sections, and the difference was strongly linked to the superficial velocity of the phases and the flow pattern. At high mixture velocity, pressure losses at the redeveloping section after the bend were higher than that at the bend and that for fully developed flows. At low mixture velocity, pressure losses at the bend are higher than in the straight sections. Pressure drop generally decreased with level of flow development downstream of the bend.

Experimental and CFD Analysis of Two-Phase Forced Convection Flow in Channels of Various Rib Shapes

This paper investigates numerically and experimentally heat transfer forced convective two-phase flow (i.e. air and water) over a rectangular ribbed channel with a vertical orientation. Three distinct rib–groove shapes have been examined. Ribs - groove shapes are; Triangle, Trapezoid, and Semi-Trapezoid ribs-groove. The present study has been performed with continuous heat flux through range of water and air superficial inlet velocity values between 0.105 – 0.316m/s, and 0.263 – 1.320 m/s, respectively. Continuity, momentum and energy calculations have been formulated using the Finite Volume Approach (FVM). Results indicate that the triangle rib-groove has the high heat transfer coefficient and lower temperature difference than other cases against a different number of Reynolds. The experimental data has been compared to numerical results for ribs –grooved channel with deviation of about 1.0% - 7.5%. The channel fitted with triangle ribs shows the highest heat transfer, which is about 59% higher than the smooth channel; 56% for trapezoidal rib, and 44% for channel fitted by semi-trapezoidal rib. Finally, the triangle rib-groove gives a better heat transfer improvement value in comparison with trapezoidal and semi trapezoidal rib-groove channel at constant pumping power.

Onset of water accumulation in oil/water pipe flow – experiments and modelling with LedaFlow

In oil/water flows with very low water rates, the steady-state water fraction jumps discontinuously from a low value to a high value when the oil rate falls below the critical value. This jump is understood to be connected to the existence of multiple solutions, and generally takes place when the oil rate becomes too low to sustain a low water fraction. We refer to this critical oil flow rate as the onset of water accumulation. Water accumulation in oil transport lines is undesirable because it can lead to corrosion problems that can threaten the integrity of the installation, potentially leading to oil leaking undetected into the environment, jeopardizing nearby wildlife and ecosystems. It is therefore critical to maintain a flow rate that is high enough to prevent water from accumulating in oil lines, and the ability to predict the minimum allowable flow rate accurately is thus of great importance. To address this challenge, a new and unique set of experiments were conducted at the SINTEF Multiphase Laboratory. The experiments were specially designed to measure the critical conditions for water accumulation in oil/water flows and were performed with a pipe diameter of 8 inches (194 mm) and a pipe inclination of 2.5 degrees. The fluid system consisted of Exxsol D60 as the oil phase and regular tap water as the aqueous phase. In these experiments, the measured critical superficial water velocities were in the range 0.1-2.6 mm/s, while the critical superficial oil velocities were in the range 0.3-0.5 m/s. We found that the customary approach of modelling the oil/water interfacial shear stress as a smooth wall was inadequate for predicting these experiments, and that interfacial waves must be considered. The data analysis showed that the onset of interfacial waves is well predicted by Viscous Kelvin-Helmholtz theory, and that a model for the interfacial shear stress can be constructed with this theory as a starting point. A new model for oil/water interfacial shear stress was developed based on this data and the associated data analysis. The new model was able to match the experimental data well and a slightly modified version of it was ultimately implemented in the commercial multiphase flow simulator LedaFlow.

Flow pattern identification and measurement techniques in gas-liquid-liquid three-phase flow: A review

The simultaneous flow of gas, oil, and water forms various flow patterns due to the complex interfacial relationships. Three-phase flow patterns are classified as the gas-liquid and liquid-liquid flow patterns. Pressure drop, void fraction, liquid holdup, and phase distribution are important characteristics of the three-phase flow. These characteristics are generally associated with the three-phase flow patterns. Hence, the knowledge about flow patterns can help to predict the overall behavior of the three-phase flow. Studies have been conducted to identify three-phase flow pattern and their characteristics at various superficial velocities of gas, oil, and water. The major purpose of the studies is to gather information about the three-phase co-current flow and use it for improvement of the efficiency of the flow systems. Therefore, the accuracy of the measurement technique is critical. Several types of flow pattern identification and measurement techniques have been developed to improve accuracy and provide high-quality results. In this article, classical and advanced techniques used for the three-phase flow identification and measurement have been reviewed. The survey will help the researchers working in the area of multiphase flow to choose the right technique based on the objectives of the studies.

The Performance Characteristics of Electromagnetic Flowmeter in Vertical Low-Velocity Oil-Water Two-Phase Flow

Since the responses of the electromagnetic flowmeter (EMF) can be affected by the flow characteristics, the combination of the EMF and the void fraction meter is always necessary for the two-phase flow measurement. Combined with a plug-in conductance sensor array (PICSA), the measurement characteristics of the EMF in low-velocity oil-water two-phase flows are investigated in this study. In a low-velocity oil-water flow experiment, the water holdup of the oil-water flows at low velocity is measured by the PICSA. By introducing correction coefficients of the EMF under different flow patterns, the correlations between the EMF responses and the oil holdup are established to measure the water superficial velocity. Finally, the oil superficial velocity is accurately predicted by a drift flux model derived from the liquid holdup and mixture velocity. Satisfactory prediction accuracy for the oil superficial velocity can be achieved without the need to introduce oil velocity measurement as in previous studies.

Systematic Frequency and Statistical Analysis Approach to Identify Different Gas–Liquid Flow Patterns Using Two Electrodes Capacitance Sensor: Experimental Evaluations

This work proposes a method to distinguish between various flow patterns in a multiphase gas–liquid system. The complete discrimination between different flow patterns can be achieved by mapping the corresponding frequency and statistical parameters. These parameters are usually obtained from further analysis conducted on the signal data of the utilized sensor. The proposed technique is based on establishing interrelationships between these parameters, namely the mean (m), the standard deviation ( σ ¯ ), power spectral density (PSD), the width of the characteristic frequency peaks (Δƒ), the skewness ( γ 1 ) and the kurtosis ( γ 2 ). Therefore, a relatively simple electrical capacitance sensor with two electrodes was designed and implemented on a two-phase flow apparatus with a circular pipe. The experimental operating conditions comprised of different combinations of air–water superficial velocities at three inclinations (i.e., horizontal, upward 15° and upward 30°). This research discusses in specific the analysis underlying flow patterns identification method and the rationale for selecting the proposed approach. The results showed that some parameters found to be more valuable than others such as m, σ ¯ and Δƒ. Besides, combining two sets of these statistical graphs which are (a) σ ¯ vs. Δƒ with Δƒ vs. m (or Δƒ vs. total power), (b) Δƒ vs. total power with γ 1 vs. σ ¯ (or γ 2 vs. σ ¯ ), and (c) σ ¯ vs. m with Δƒ vs. m (or Δƒ vs. total power), allowed all flow patterns field to be identified clearly at all inclinations. It is therefore concluded that for any gas–liquid multiphase flow system, the reported approach can be used reliably to discriminate between different generated flow patterns.

Experimental study on gas-liquid-liquid three-phase flow patterns and the resultant pressure drop in a horizontal pipe upstream of the 90° bend

The use of 90˚ bend for diversion of flow in different orientations is widespread. The current study is focused on the effect of 90˚ bend on gas-oil–water three-phase flow in an upstream horizontal pipe. The diameter of the test section is 0.1524 m, and (R/d) ratio of the bend is 1. The ranges of superficial velocities of gas, oil, and water were 0.5–5, 0.08–0.36, and 0.08–0.36 m/s, respectively. The observed gas–liquid flow patterns are slug, pseudo-slug, stratified wavy, stratified roll wave, and stratified flow. The oil and water were observed to be flowing as a separate, partially mixed, and fully mixed liquid. Flow regime maps have been plotted to analyze the transition of flow patterns. The variation in pressure drop with the flow patterns has been studied. The experimental data has been used to develop pressure drop prediction correlation and the comparison with experimental results showed good agreement.

Measurement of Water Velocity in Gas-Water Two-Phase Flow with the Combination of Electromagnetic Flowmeter and Conductance Sensor.

A method to measure the superficial velocity of the water phase in gas–water flow using an electromagnetic flowmeter (EMF) and rotating electric field conductance sensors (REFCSs) is introduced in this paper. An electromagnetic flowmeter instrument factor model is built and the correlation between electromagnetic flowmeter output and gas holdup in different flow patterns are explored through vertical upward gas–water flow dynamic experiments in a pipe with an inner diameter (ID) of 20 mm. Water superficial velocity is predicted based on pattern identification among bubble, churn, and slug flows. The experimental results show that water superficial velocity can be predicted fairly accurately for bubble, churn, and slug flows with a water cut higher than 60% (absolute average percentage deviation and absolute average deviation are 4.1057% and 0.0281 m/s, respectively). The output of the electromagnetic flowmeter is unstable and invalid in slug flows with a water cut below 60% due to the non-conducting gas slug is almost filling the pipe. Therefore, the electromagnetic flowmeter is not preferred to be used in such conditions.

Investigation of the Effect of Fluids Superficial Velocity on Initiation and Development of Slug Flow in a Horizontal Hydraulics Pipe

The aim of this study is to investigate the effect of fluids superficial velocity on the characteristics of two-phase slug flow in a horizontal hydraulics pipe covering slug flow initiation and development. Air and water were employed as the working fluids. Slug flow characteristics were visually observed at 25D and 200D in a 19 mm internal diameter of acrylic pipe for the initiation and fully developed slug flow conditions, respectively. Flow visualization was taken using high speed video cameras at 400 fps and then analyzed using image processing method. Based on the flow pattern characteristics, several slug flow initiation mechanisms were obtained. Under the investigated conditions, at low to medium air superficial velocity (JG) with low to high water superficial velocity (JL), slug flow initiation mechanisms consisted of wave growth, hydraulic jump, blockage, and slug decaying. While wave initiation, wave formation, disturbance, wave coalescence, and incompletely developed slug mechanisms were observed at medium to high JG with low to high JL. After slug flow was fully developed, it was found that the higher the water superficial velocity resulted in lower void fraction and higher slug frequency. In the meantime, pressure drop and liquid slug velocity increased considerably with the increase of both JG and JL. Maximum pressure drop of 8.35 kPa/m occurred at JL of 2.00 m/s and JG of 3.76 m/s. The highest slug frequency of 6.67 1/s was observed at JL of 2.00 m/s and JG of 2.12 m/s. This information is important for designing fluid flow in horizontal hydraulics pipes and for consideration in predicting the development of the slug flow in order to avoid the negative impact of slug flow in industrial applications.

Study of intermittent flow characteristics experimentally and numerically in a horizontal pipeline

The gas-liquid intermittent flow regime is the dominant flow pattern, which significantly occurs in the oil and gas industries. The intermittent flow is challenging in the hydrocarbon transportation systems and separators operation. The present investigation aims to comprehend the behavior of intermittent flow characteristics using experimental and numerical methods simultaneously. Superficial velocities of water and air were set in ranges of (0.18–0.84 m/s) and (1.22–4.9 m/s), respectively. The research was conducted in a horizontal pipe with a diameter of 44 mm and 147D long to study slug frequency, slug length, translational slug velocity, pressure drops, as well as slug's initiation location using static pressure data and high-speed camera tools. In this regard, the volume of fluid (VoF) method and SST k-ω model were also applied to specify film thickness, maximum Taylor bubble velocity, and to grasp behaviors of the flow field in more detail. The results revealed that liquid superficial velocity has more effects on slug frequencies than gas superficial velocity. On the other hand, slug initiation location, as well as slug fully developed length, is affected by the gas superficial velocity more than liquid superficial velocity. Moreover, both the gas and liquid superficial velocities have the same effects on translational slug velocities. The obtained experimental results were also employed to define a distinctive inlet boundary condition in the numerical simulation, which leads to a 65 percent reduction in the computational domain.

Experimental and Numerical Studies of Two-Phase Flow in Ribbed Periodic Vertical Channel

Pressure drop in a ribbed vertical channel was studied for a two-phase (air and water) flow, different shapes of ribs (triangle, semi-circular, and rectangle) were used in this investigation. An experimental rig was constructed with a test channel having the dimensions (10×3×70 cm) that enabled the flow patterns visual observation. An experimental setup of a two-phase was done for the present investigation, as well as a sum of (150) two-phase data with various flow patterns was determined. The used water superficial inlet velocities were in the range (0.0333 - 0.0888 m/s), and the air superficial inlet velocities were in the range (0.0555 - 0.1666 m/s). The experimental pressure drop according to a smooth plate was (41%, 38%, and 35%) for a channel fitted with semi-circle, rectangular and triangular ribs, respectively. The less pressure drop recorded was in the triangular ribbed channel, which indicates that the triangular shaped ribbed channel is the finest shape among the studied ones to lower the pressure drop. As future work, the numbers and dimensions of ribs can be changed to investigate its effect on the two-phase flow and the pressure drop, another suggestion for the future investigations is to include other fluid to have a three-phase flow, also the inclination angle of the duct can be changed to study its effect.

Gradual contraction of pipe cross-section effects on transient behavior of air–water slug flow

The current experimental investigation was aimed at understanding the influence of reducing sections on the transient behavior of slug flow. Experiments were carried out using two concentric area cross-section reducers with 160 mm lengths; the first one was shaped as a conical frustum with a 44 mm inlet diameter reducing to a 30 mm outlet diameter and the second one as a frustum with the same inlet diameter converting to a rectangular cross-section (34 mm × 21 mm). Four different water superficial velocities (0.43, 0.55, 0.72 & 0.84 m s−1) and three different air superficial velocities (2.5, 3.6 & 4.9 m s−1) were applied in the course of the experiments. Visualization studies, as well as frequency distribution analyses, were used to observe flow field changes. The visualization study showed that the gas slug tail, liquid slug, and gas slug subsequent to passing through the reducers converted to non-homogeneous bubbly flow, several small slugs, and pseudo-slugs, respectively. The obtained frequency distributions, which were calculated using a Fourier transform tool, showed that unlike that of the dominant frequency, the power of other frequencies was amplified in the low-frequency range owing to the high formation rate of pseudo-slugs and small slugs. This change indicates that intermittent air–water slug flow with a specified dominant frequency subsequent to passing reducers varies to an uncertain flow with semi-uniform distribution in the low-frequency range. Estimation of Shannon entropy also showed that entropy increased by almost five times downstream of the reducers, which confirms that energy is distributed uniformly in a broad frequency bandwidth. Analyses of the essential bandwidth showed that the reducing section acted as a frequency distribution modifier whose performance decreased with liquid flow rate increments. Based on this achievement, it was found that both the circular and the rectangular reducers were able to generate the named conditions.

Single- and two-phase pressure drop through vertical Venturis

An experimental investigation of the pressure drops measurements in a Venturi placed in a vertical pipe is achieved. Venturis with diameter ratios equal to 0.4, 0.55, and 0.75 were employed. Differential pressure transducers were used to measure the pressure drop between the Venturi inlet and the throat sections. The void fraction was measured upstream the Venturi using a conductance probe technique. Air and water superficial velocities ranges were chosen to cover single-phase flow and bubbly, slug, and churn flow regimes. The single-phase pressure drop increases with the liquid superficial velocity. The Venturi pressure drop coefficient increases with decreasing the Venturi area ratio. The discharge coefficient increases slightly with this ratio and approaches a value of unity at high Reynolds number. The two-phase flow pressure drop and the multiplier coefficient increase with the gas superficial velocity and with decreasing the area ratio. Dimensionless pressure drop decreases with increasing the liquid to gas superficial velocity ratio and approaches an asymptotic value at high ratio (greater than 10). This value matches the single-phase flow dimensionless pressure drop value at high Reynolds number. The Venturi with area ratio equal to 0.55 was shown to correlate well the two-phase multiplier and the liquid holdup.

Effect of superficial air and water velocities on the erosion of horizontal elbow in slug flow

During the development of oil and gas fields, it is common for elbow suffering from sand wear. In this study, the erosion performance of 316 L stainless steel at the elbow was analyzed using the slug flow erosion experiment loop. The experiment was conducted under slug flow with different superficial air and water velocities using a detachable elbow. After weighing the mass loss and analyzing the sample surface, the erosion rates in different parts of the elbow were quantified and the erosion regularity was analyzed. The results indicate that the increase in superficial air velocity has a greater impact on the erosion rate than that in the superficial water velocity. The maximum erosion damage occurs at the outer wall in the 67.5° position. With the increase in superficial air and water velocity, the number of scratches on the maximum erosion position reduces.

Nutrient (sulphate) removal from wastewater in inverse fluidized bed biofilm reactor

Sulphate is one of the inorganic nutrient pollutants present in wastewater which needs to be treated due to present day global stringent emission norms. Among the several available biological means to treat industrial wastewaters, the use of inverse fluidized bed biofilm reactors (IFBBRs) has gained much attention in recent years over other fluidized bed reactors. In this work, the feasibility of removal of sulphate from synthetic wastewater having initial concentrations of 13.096, 32.74, and 65.48 mg/l was studied using mixed bacterial culture. Spherical polypropylene balls were taken as biomass support particles having density of 920 kg/m3 and diameter of 5.63 mm. Three different bed-volume to reactor-volume (Vb/Vr) ratios i.e., 0.304, 0.380, & 0.445 and three different superficial air velocities i.e., 0.0065, 0.0085, & 0.0106 m/s were considered for experimental runs. The reactor inoculum was prepared from the sludge collected from local steel industry’s wastewater treatment plant. The effects of different input parameters such as Vb/Vr ratio, superficial air velocities, and initial concentration of sulphate in synthetic wastewater on the output sulphate concentration were studied. Temperature of 30–32 °C and pH of 8.3–8.8 were maintained throughout the degradation studies. The reactor was operated in semi-batch recirculation mode with superficial water velocity of 0.0021 m/s. Sulphate concentration was measured by turbidity method using UV spectrophotometer at 420 nm which is as per APHA standards. The maximum removal efficiency of sulphate was found to be 72–75% which was achieved at a Vb/Vr ratio of 0.380 and the superficial gas velocity of 0.0085 m/s observed at a time of 40 h. Higher sulphate reduction was not achieved due to presence of more inorganic salts in the synthetic wastewater. At higher initial sulphate concentration, reactor operational difficulties were observed.

Experimental investigation of two-phase separation in a horizontal T-junction with vertical branch arm

T-junctions are commonly used in offshore platforms and process industry. When two-phase flow passes through T-junction, separation of two-phases takes place. This separation of two-phase flow through T-junction produces high liquid carry-over in the branch arm, causing breakdown of downstream equipment. In this experimental study, phase separation data have been obtained for air-water mixture flow through dividing T-junction with a pipe diameter of 74 mm and the branch arm is positioned vertically upward. T-junctions with diameter ratios of 1, 0.67, 0.5, and 0.27 were tested in the slug flow regime. The superficial velocities of air (JG1) were varied 0.20 - 1.16 m/s and inlet water superficial velocities (JL1) were varied 0.40-0.53 m/s. The extraction ratio between branch arm and main arm (W3/W1) was varied between 0 to 1. It was observed that the phase separation efficiency of T-junction depends upon the diameter ratio, upstream superficial velocities of both phases - air and water. Finally, the experimental data have been compared against the predicted results obtained from the numerical correlations.

Phase split of oil-water two phase flow at double-layer T-junctions pipes

Offshore oil and gas production systems are in urgent need of a more compact, high-efficient oil-water separator. T-junction pipes are a potential solution to the need. Combining dynamic separation principle of T-junctions pipes with shallow pond theory, this paper presents a novel design of double-layer T-junctions pipes to realize high-efficient oil-water separation. The separation system consisted of upper and lower double-layer pipes that are connected by two vertical pipes. There exists an axially floating oil pipe along the top of the upper outer pipe. This design makes the Reynolds number decrease, which is beneficial to the formation of oil-water stratified flow. The slender seam at the bottom of inner pipe reduces the turbulence intensity, thus avoiding remixing oil with water. The influence of mixture velocity, oil content, water superficial velocity, oil superficial velocity, and inlet flow pattern on the phase split of oil-water two phase flow at double-layer T-junctions pipes has been investigated. Experimental results showed that the separation performance was less affected by the inlet oil content than by the inlet mixture velocity. Additionally, the phase split in the separation system was very sensitive to the inlet flow pattern. For separated flow pattern, oil-water can be well separated. But for dispersed flow pattern, the oil-water separation efficiency was low. Besides, the using of floating oil pipe can increase the system separation efficiency.