Flow Pattern Map Research Articles

Experimental Study on Gas-Liquid Two-Phase Stratified Flow at High Pressure in a Horizontal Pipe

This study investigates wave-stratified flow in a horizontal pipe at high pressure, and flow characteristics are obtained, such as flow pattern map, liquid film thickness, and pressure drop. Compared with a flow pattern map of a gas-liquid two-phase flow carried out at atmosphere, stratified flow zone is depressed with increasing system pressure and the critical gas superficial velocity decreases for smooth-wave-stratified flow transition, while the critical liquid superficial velocity increases for stratified-intermittent transition. On one hand, the compressed air results in an increase in momentum transfer between gas and liquid phases, which accounts for the smaller gas superficial velocity that is encountered in both smooth-wave and stratified-annular flow transition at higher pressure. One the other hand, it slows down the liquid below the crest, and it makes the interface wave crest unstable and split for the vortex shedding behind the wave crest, which accounts for flow regime transition in gas-liquid two-phase flows in pipelines. As a result, stratified-intermittent flow transition is depressed and delayed. The pressure influence on the liquid film profile is analyzed, and relationships between film thickness and dimensionless numbers are studied, such as liquid Weber number and gas Weber number. Friction factors on different interfaces at high pressure are studied, and new empirical formulas are deduced.

Exploring the correlation between inclination angle and flow pattern transition in oil-water flow

The impact of pipe inclination angle on oil-water flow regimes transition boundaries is vital in various engineering applications, including pipeline and separator inlet design. Understanding this influence is crucial for identifying alternative and optimal designs. The standard way of presenting oil and water superficial velocities on 2D flow pattern maps doesn't consider how the flow pattern varies with pipe tilt angle. This article aims to clarify how the angle of pipe inclination affects oil-water flow regime transitions. This method uses pipe inclination angle as a direct representation, with the angle shown on the x-axis of a 2D flow pattern map, which has not been done before in literature. The y-axis, or ordinate, is a dimensionless number that accounts for mixture velocity, fluid densities, and pipe diameter. Two dimensionless numbers were utilized. The Froude number based on mixture velocity, FrM, and the Reynolds number (ReOM) based on mixture velocity and oil properties, are plotted against pipe inclination angle. The evaluation and validation of the proposed methods for the effect of the inclination angle were performed using a database of more than 10,000 points established from studies reported in the literature. The findings show that both the Dispersed (DF) and Semi-Dispersed flow regimes (SDF) exhibit higher FrM values than smooth stratified regardless of the pipe's incline. Moreover, the spreading area is symmetric around the horizontal line which means that the DF and SDF can be observed at similar FrM for both positive and negative inclinations. Focusing horizontally, FrM is highest for ST-MI, lower for SW, and lowest for ST. This paper also presents and demonestrates a case study showcasing a new application for flow pattern maps, illustrating their potential in design purposes.

Flow pattern maps of double emulsions transporting through bifurcation microchannels.

The transportation behaviors of compound droplets in confined channels are widespread phenomena while the physical mechanisms are far from being completely unraveled. In this work, behaviors of double emulsions flowing through bifurcation microchannels are experimentally studied with the aim of building universal flow pattern maps. Three flow patterns are categorized according to different features of daughter droplets in terms of size, uniformity, and shell thickness. A detailed analysis of the dynamics of interfacial evolutions in different patterns is carried out and the coupling interaction between interfaces is found to affect the minimum tail distance during transportation. It is feasible to obtain the threshold of the occurrence of the coupling interaction, due to the different variation tendencies in the two states, which relies on three dimensionless parameters, i.e. droplet length, length ratio, and capillary number. Furthermore, a novel physical model is proposed to build the flow pattern map, with the two transition boundaries being expressed as different relationships in terms of the three identified parameters. The physical mechanisms are summarized with the aid of force analysis. An excellent agreement is shown between the model and experimental results in different liquid systems and bifurcation structures, indicating the generality of the proposed model.

IDENTIFICATION OF WAVY FLOW SUB-REGIMES USING POWER SPECTRUM OF LASER DOPPLER VELOCIMETRY SIGNALS

The formation of a slug happens when the roll waves on the interface of two-phase flow undergo constructive interference. Slug flowing with high momentum results in flow-accelerated corrosion (FAC) leading to cracks in pipes. The leakages from such cracks are hazardous to industry. In order to avoid such hazards, a detailed analysis is required for the transition of smooth stratified flow to slug flow. This transition happens through different wavy flow sub-regimes. Previous studies in literature used visual observation and image processing to determine sub-regimes of wavy flow. However, visual observation alone is not sufficient to differentiate between the different sub-regimes of wavy flow. In the present study the power spectrum of the velocity signals measured using laser Doppler velocimetry (LDV) is used in addition to visual observations to develop a precise wavy-flow sub-regime map. Experiments are conducted in a two-phase flow test rig by varying liquid superficial Reynolds number in the range of 1685 and 6830 and gas superficial Reynolds number between 393 and 9824. The transition to wavy flow is observed much earlier in the present study compared to that reported in literature based solely on visualization methods. The present paper successfully utilized power spectrum analysis to accurately and precisely categorize wavy flow sub-regimes, including the creation of a flow subregime map demarcating "3D large-amplitude waves (3DLA)," "2D small-amplitude waves (2DSA)," "3D small-amplitude waves (3DSA)," and "2D large-amplitude waves (2DLA)." The modified flow-pattern map developed based on power-spectrum analysis of velocity signals and the flow visualization is compared with the flow-pattern maps available in literature.

Vertically downward gas-liquid flow: Void fraction and pressure drop

Using an air-water mixture and 34 mm ID pipe, a series of pressure drop and void fraction measurements were collected. The observed flow regimes were falling film, annular, bubbly, cap bubble, slug, and churn flows. The temporal fluctuations of void fraction and pressure drop measurements were firstly studied using signals visualization and PDF. It was revealed that both signals can be used to identify the flow regimes. A new flow pattern map is proposed based on the Froude number, calculated using the mixture velocity of the two phases, and the ratio of gas-to-liquid superficial velocities. The behaviors of the total and frictional pressure drops were studied and the influence of the superficial velocities as well as the flow regimes were identified. The experimental results were compared to four existing vertically downward frictional pressure drop models, none of which provided accurate predictions.

A comprehensive study with high-speed camera assisted visualizations of HFO-1234ze(E) condensation inside an enhanced tube

Flow condensation of HFO-1234ze(E) inside a helical micro-finned tube of 4.28 mm ID underwent experimentation. Flow patterns were visualized with a high-speed camera while varying vapor qualities from 0.01 to 0.95 and mass fluxes from 100 to 400 kg m−2 s1, at saturation temperature of 30 °C. Intermittent, stratified-wavy, transitional, and annular flow pattern types were identified. The flow pattern map of Doretti et al. (validated by Cavallini et al.) accurately predicted the flow patterns. Heat transfer coefficients (HTCs) and frictional pressure drops (FPDs) were also measured for mass fluxes ranging from 100 to 600 kg m−2 s−1 at saturation temperatures of 30 °C and 40 °C. Both HTC and FPD elevated with higher mass fluxes and vapor qualities which stemmed from the presence of observed shear stress-driven annular flow patterns. HTC and FPD are generally higher at lower saturation temperatures. Experimental HTC and FPD have been compared against values estimated with empirical models. Furthermore, the average enhancement factor of the micro-finned tube was 2.94 with an area enhancement factor of 2.39. Plotting enhancement factor versus non-dimensional gas velocity provided detailed insight into the augmentation effect of micro-finned tubes under different operating conditions.

Experimental study of viscous oil-water core-annular flow in horizontal pipe

Transporting viscous oils through pipelines is usually challenging due to their very high viscosity. Significant friction reduction in the transportation of viscous oils through pipelines using an ecologically friendly way is the most appealing feature of the core annular Flow (CAF) technique. An experimental study has been conducted to investigate the flow patterns and pressure gradient of viscous oil-water two-phase flow in a horizontal acrylic pipe with a 50 mm inner diameter. The test section was equipped with a fluid lubrication injector element to artificially provide CAF. The pressure gradient measurements were focused on the CAF pattern. The prediction models of the CAF pressure gradient were reviewed and evaluated. An empirical prediction model of CAF pressure gradient was developed, relying on both the present and previously published experimental results. The flow patterns were classified into five patterns. It was observed that the CAF occupied a large region in the constructed flow pattern map and its frictional pressure gradient closely resembles that of water flowing alone. It was found that the developed empirical model provided quite good predictions of the experimental pressure gradients and significantly outperformed the original model. The reviewed prediction models in this area for CAF either overpredicted or underpredicted the experimental pressure gradients. Some of these models considered the extensive effect of viscous oil adhered to the inner wall of the pipe, while others neglected the effect entirely.

The effect of fluid properties on development of two-phase flow after an expansion valve based on the comparison of R245fa and R134a

This paper analyzes the developing adiabatic two-phase flow after an expansion valve in an air conditioning system. R245fa and POE 32 mixture is used as the working fluid. The developing two-phase flow patterns are visualized in an 8 mm straight tube after the expansion valve from 15 to 595 mm. To explore the effect of fluid properties on the developing two-phase flow, the experimental results from previous research by the same authors are compared with those of R245fa in this paper. An image analysis technique and a one-dimensional developing two-phase flow model proposed in a previous paper by the same authors (Yao & Hrnjak, 2023c) are applied to both R134a and R245fa. The flow patterns near the expansion valve exhibit some similarities when comparing the two refrigerants. However, a significant contrast emerges in the presence of a greater number of droplets suspended within the vapor phase in the case of R245fa flow. This disparity is primarily attributed to R245fa's higher vapor velocity. Furthermore, R245fa exhibits a shorter developing length than R134a. For fully developed flow, R245fa showcases a more pronounced turbulent behavior, and the transition to annular flow happens at a lower vapor quality in comparison to R134a. All of these distinctions can be adequately accounted for by the proposed model. The developed flow patterns of both refrigerants are compared with some existing flow pattern maps. At last, a new flow pattern map is proposed based on the observed flow patterns in this research.

Hydrodynamic characteristics of core/shell microdroplets formation: Map of the flow patterns in double-T microchannel

Liquid-liquid–liquid (L/L/L) flows in microchannels involving three-phase interactions are important in various chemical applications that entail liquid–liquid–liquid reactions. This work comprehensively investigates core (silicone oil)/shell (Polycaprolactone) microdroplet formation using a continuous third phase (distilled water) in a double T-junction microchannel with a diameter of 600 µm, employing Volume-of-Fluid (VOF) simulations and high-speed imaging experimental observation. Due to the satisfactory agreement between computational and experimental techniques, the theoretical flow patterns were identified and categorized into three distinct categories at various flow rates of three phases: core/shell dripping, core/shell slug, and core/shell jetting. The shell thickness increases as the ratio of shell to core phase velocity (ushell:ucore) increases. Based on the continuous phase Capillary number (Cac) and core and shell phases Weber number (Wecore,shell), a flow pattern map was generated that segregates the distinct flow patterns into different regions. When the flow of the core and shell phases fails to form a droplet due to the inertia of the continuous phase, a core/shell dripping/slug pattern is observed. The channel walls encompass the droplets that form in the slug pattern (2×10-5≤Cac≤5×10-4, 0<Weshell≤1.5×10-3, and 0<Wecore≤5×10-5) because the continuous phase has less inertia, whereas, in the dripping pattern (5.5×10-5≤Cac≤9×10-4, 7×10-5≤Weshell≤2.5×10-4, and 1×10-5≤Wecore≤7×10-5), the shell phase fluid is enclosed by the continuous phase. The transition from dripping to jetting (Cac≥0.5, 0<Weshell≤0.15, and 1×10-2≤Wecore≤8×10-2) occurs as the flow rate of a continuous fluid or shell fluid increases. A dimensionless correlation for shell thickness estimation with a 12 % tolerance was proposed with a core/shell/continuous phase's physical properties, surface tensions, and microdroplet size, using Buckingham's theory based on 200 CFD simulations. Additionally, the flow rate and viscosity substantially impact the internal fluid velocity and vorticity of core/shell microdroplets, whereas the influence of interfacial tension can be disregarded. This research lays the groundwork for future studies on mass transfer and reaction behaviors in liquid–liquid–liquid three-phase flow in double T-junction microchannels by exploring various hydrodynamic characteristics under different operating conditions for core/shell microdroplet formation.

Air Bubble Size and Its Transition in a Horizontal Tube Produced by Venturi-Nozzle Bubble Generator

This paper investigates the air bubble size and its transition in a horizontal tube of 700 mm. The tube was assembled with a venturi-nozzle bubble generator. Air and water flow-rates vary in the present study. The data collection mainly used high-speed camera to capture the bubbles at different distances along the horizontal tube at water flow-rates (Qw) of 120-170 litre per min (LPM) and air flow-rates (Qa) of 2-10 LPM. MATLAB was used in image processing for evaluating the bubble size. The data interpretation used YW dimensionless parameter in representing the height of the bubbles’ vertical rise in the horizontal tube. The bubble size along the horizontal tube was characterized by the Weber number as well. The type of two-phase (water-air bubbles) flow along the horizontal tube from the venturi-nozzle bubble generator was determined using flow pattern map and Lockhart-Martinelli parameter. The bubble generator produced bubbles in the range of 0.8-3.1 mm at the inlet of horizontal tube. The bubble diameters increased as the bubbles moved horizontally from inlet to outlet of the horizontal tube and this finding was statistically significant. The vertical rise height of bubbles along the horizontal tube at different water and air flow-rates had been quantified and compared. The vertical rise height of bubbles increased axially from 41 % to 89 % from inlet to outlet of the horizontal tube. The bubbles’ vertical rise height increased when either the air flow-rate or water flow-rate is reduced. The mean Weber number increased along the horizontal tube due to an increase in bubble size. The decrease in water flow-rate caused a decrease in the mean Weber number. The Lockhart-Martinelli parameter of the water-air bubbles flow in the horizontal tube was within 0.58-2.94, indicating that it was a multiphase flow. The findings from this study give fundamental insight into bubble dynamics behaviour in its horizontal transition. This study focuses on the size and transition of air bubbles produced by venturi-nozzle bubble generator along a horizontal tube at different water and air flow-rates, unlike previous studies which only investigate the air bubbles inside or near bubble generator. These findings are very useful for practical industrial applications because the exact air bubble size before being used is known.

Flow boiling heat transfer characteristics of zeotropic mixture CO2/R152a with large temperature glide in a 2 mm horizontal tube

The flow boiling characteristics of CO2/R152a zeotropic mixtures with three mass fractions (22.1/77.9, 47.4/52.6 and 65.3/34.7 wt.%) and the pure components in a 2 mm horizontal tube are experimentally studied. The flow boiling characteristics are tested in the range of temperature glide of 30.9∼38.3 °C, mass flux of 200∼400 kg/m2s, heat flux of 12∼36 kW/m2, and saturation temperature of 5∼15 °C. Flow patterns are observed and the flow pattern map is also described, and the heat transfer and pressure drop characteristics of working fluid are also conducted. Furthermore, a new correlation to predict the heat transfer coefficient of large temperature glide working fluid is proposed. The results show 7 types of flow patterns are recorded, showing the flowing characteristic between the conventional and microscale channel. The heat transfer coefficient of CO2/R152a increases slowly with vapor quality, and decrease rapidly when vapor quality reaches to the initial dryout vapor quality, which is lower than that of pure CO2. The mass transfer resistance and sensible heat resistance shows a severe deterioration effect on the flow boiling heat transfer due to the high temperature glide as the sensible heat accounts for 13.12∼15.44 % for the mixture CO2/R152a. The frictional pressure drop gradient of CO2/R152a increases with mass flux, and decreases with the increase of saturation temperature and mass fraction of CO2. Considering the mass transfer resistance and effects of non-negligible sensible heat contribution, a new heat transfer correlation is proposed, with the mean absolute deviation of 16.9 %, which shows an acceptable prediction accuracy compared with the reported data in the literatures.

Effect of Lateral Trajectory on Two-Phase Flow in Horizontal Shale Gas Wells

Horizontal gas wells are one of the key technologies for the production of shale gas reservoirs. Compared with conventional gas reservoirs, horizontal shale gas wells have ultra-long and complex lateral sections. Overall, toe-up, toe-down, and horizontal trajectories will be exhibited in the lateral section. The statistical results of field production data indicate that the lateral trajectory has a significant impact on the estimated ultimate recovery. However, the mechanism has not yet been fully revealed owing to the complicated two-phase flow in lateral pipes. Therefore, taking horizontal shale gas wells’ lateral section as the research object, we designed our experimental parameter ranges based on horizontal shale gas wells in the Changning shale gas field. Simulation experimental tests were conducted on the pipe with an inclined angle from −15° to 15° to analyze the effects of different gas velocities, liquid velocities, and pipe inclinations on flow patterns and liquid holdup. Based on our observations and measurements, we evaluated the flow pattern prediction methods and drew a new flow pattern map for pipes with an inclined angle from −15° to 15°. Based on the momentum conservations between the gas and liquid phases and measured liquid holdup data, a new liquid holdup model was established in the pipes with inclined angle from −15° to 15°. Experimental and field-measured data were collected to verify the new method’s accuracy.

Extractive Desulfurization in Microchannel Contactors Using Deep Eutectic Solvents: Optimization Using Central Composite Design (CCD) and Flow Pattern Mapping

Extractive Desulfurization in Microchannel Contactors Using Deep Eutectic Solvents: Optimization Using Central Composite Design (CCD) and Flow Pattern Mapping

Development of boiling flow pattern map and heat transfer correlation of R32-oil mixture inside a horizontal micro-fin tube

R32 has been widely applied in room air-conditioners (ACs) because of its low GWP, and its heat transfer characteristics in refrigeration cycles may be affected by the lubricating oil mixed in R32. To quantitatively evaluate the effect of oil on the flow boiling heat transfer characteristics of R32, the flow pattern map and heat transfer correlation of R32-oil mixture are needed. In this study, an experimental rig for R32-oil mixture is established, in which the boiling flow patterns are observed and the heat transfer coefficients are measured. The experimental conditions cover the evaporation temperature ranging from -5 to 15 °C, mass flux ranging from 100 to 400 kg m−2s−1, vapor quality ranging from 0.1 to 0.9 and oil concentration ranging from 0% to 5%. A total of 80 flow patterns and 336 heat transfer coefficients have been obtained under the above experimental conditions. The results show that the flow patterns of R32-oil mixture contain stratified wavy flow, intermittent flow, annular flow and dryout flow, and the presence of the oil could promote the transformation from stratified wavy flow to annular flow; the heat transfer would be enhanced by the oil under lower vapor qualities and be deteriorated under higher vapor qualities. The boiling flow pattern map is developed based on observation results, which could well predict the flow patterns under the experimental conditions. The heat transfer correlation is developed based on the flow patterns and could predict 82% of the experimental results within a deviation of ± 20%.

Study on characteristics of phase-isolation caused by different classic axial flow swirlers in upward vertical gas-liquid two-phase flow

The characteristics of phase-isolation of annular flow caused by axial flow swirler are very critical for separation efficiency of axial inlet separator and accuracy of phase-isolation based measurement method. However, there are lack of comparative study among different types of swirlers and research focusing on characteristics of phase-isolation. In this paper, the phase-isolation characteristics caused by four different classic axial flow swirlers with the same main structural parameters were firstly experimentally studied in upward vertical gas-liquid two-phase flow. Five flow patterns were proposed after obvious evolution in phase distribution at downstream of the swirler, including gas-column flow, swirling annular flow, central bubble flow, central bubble-column flow, and variable diameter gas-column flow. According to the different phase-isolation characteristics, flow patterns downstream of the swirler were divided into stable phase-isolation, quasi-phase-isolation, and non-effective phase-isolation. The corresponding flow pattern maps were also obtained respectively. The experimental results also show that the swirler with good phase-isolation performance generally requires a larger pressure drop as the cost. Finally, the flow in the swirlers was studied numerically. It is found that although the outlet angle of the swirlers is the same, different types of swirlers will result in flow with different deflection angle, and eventually cause the different phase-isolation performance.

Flow patterns and dynamic mechanisms of immiscible fluids in cross junctions with different aspect ratios

The flow patterns of immiscible liquids in microscale cross junctions are experimentally studied and the influencing factors including the capillary number (3 × 10−4–6 × 10−1), flow rate ratio (0.004–60), viscosity ratio (0.04–2.8), and channel aspect ratio (1/3–1) are systematically analyzed. Evolutions of the interfacial morphologies in different flow patterns are discussed with the aid of force analysis. In the droplet group, two different breakup modes of the liquid thread are found with the symmetric mode for squeezing and the asymmetric mode for dripping, which are divided by a critical capillary number around 0.01. Two different physical models for constructing the scaling law of the droplet length are compared over large ranges of flow parameters and the universal scaling law is valid to identify the transitional boundary between squeezing and dripping regimes. In the jet group, the jet width in different channels is compared to the theoretical prediction. A detailed comparison between the experimental results in jetting and the linear instability theory is further conducted and the reason for the polydispersity of the droplet size in widening jetting is found. Finally, the flow pattern maps are built using dimensionless parameters in both the global terms and the local terms. In contrast, the local dimensionless parameters are confirmed to show a better performance in unifying the transitional boundary between two groups of flow patterns. The obtained results should be useful for the further understanding of the dynamic mechanisms of the microscale multiphase flow.

Liquid–Liquid Two-Phase Flow and Size Prediction of Slug Droplets in Microchannels

The liquid–liquid two-phase flow and size prediction of slug droplets in flow-focusing microchannels with different downstream orifice sizes were investigated experimentally. Aqueous solution of 50%-glycerol and mineral oil with 4 wt.% surfactant sorbitanlauric acid ester (Span 20) were used as the dispersed and continuous phases, respectively. Three characteristic flow patterns were identified: slug flow, dripping flow, and jetting flow. The slug flow region decreased but the jetting flow region increased with the decrease in the size of the channel orifice. Afterwards, the universal flow pattern maps of the liquid–liquid two-phase in three microchannels were obtained based on dimensionless analysis. Furthermore, two slug droplet formation regions were found: when φ−1Cac &lt; 0.01, the droplet formation was mainly driven by the squeezing force Fp, while when φ−1Cac &gt; 0.01, both the squeezing force Fp and shear force Fτ contributed to droplet formation. Additionally, the prediction correlations of the dimensionless sizes of the slug droplets in both regions were established based on the flow rate ratio of the two-phase, the dimensionless orifice size, and the Capillary number of the continuous phase. The predicted results are in good agreement with the experimental values.

Experimental investigation on interface characteristics of gas-liquid two-phase flow in a kilometer-scale pipeline

It is greatly essential for the construction of multiphase flow models and the flow assurance of oil and gas pipelines to study the fully developed interface characteristics at different flow patterns in the industrial-grade long-distance pipelines. In this paper, the phase interface structures of dispersed bubble flow and three slug sub-flow patterns are captured by visualization method in a 46 mm ID, 1657 m long pipeline. It is found that the interface characteristics between elongated bubbles and liquid film can effectively distinguish different slug sub-flow patterns, and a quantitative division criterion between different slug sub-flow patterns is proposed. The transition boundary prediction model for dispersed bubble flow and slug flow in long pipeline is established, and the flow pattern map at high liquid velocities and low gas velocities is plotted. With the increase of two-phase mixture velocity, the radial position of elongated bubble head approaches the middle of the pipeline, and the liquid film thickness is stably distributed around 0.37 D. The correlations that predict the radial position of elongated bubble head, liquid film thickness, and elongated bubble velocity for long pipeline are established, with maximum error less than 15 %.

Application of nonlinear dynamics analysis to gas-solid flow system in horizontal pneumatic conveying of plastic pellets

Chaotic invariant and recurrence quantification analysis measures have characterised fully developed gas-solid flow in horizontal pneumatic conveying of plastic pellets. These measures describe the complexity in phase spaces (attractors) and recurrence plots, reconstructed from pressure and bottom arc-shaped electrostatic signals to characterise the behaviour of flow patterns. Different flow patterns were identified using high-speed video imaging of a transparent pipeline and classified at several operating conditions in a flow pattern map and state diagram. Recurrence plots were analysed for the identified flow patterns, which showed different qualitative structures. The chaotic invariant and recurrence quantification analysis measures were correlated with the state diagram, indicating that the fluctuations of pressure senor and electrostatic sensor signals can classify the flow patterns at different operating conditions. Combining the analysis measures for electrostatic signals can indicate whether the flow condition is above, near or below the minimum energy consumption operating conditions.

Experimental quantification of the performance of a horizontal multi-pipe bulk separator of water and oil with crude spiking

Subsea water separation with pipe separators is crucial for ensuring efficient and environmentally responsible extraction of oil and gas from the seabed. In this study, in a process called as “crude oil spiking,” two concentrations of crude oil (e.g., 185 and 400 ppm) are added to Exxsol D60 to mimic the separation characteristics of real crude oil mixtures in a multi-parallel pipe separator. The pipe separator performance for water–oil bulk separation such as separation efficiency, water cut ratio, the flow pattern at the separator inlet, and the thickness and evolution of the fluid layers in the separator is evaluated and compared to the values when operating with unspiked Exxsol D60. Crude oil spiking significantly reduces the efficiency of the pipe separator and reduces the water cut ratio for oil continuous regimes (low water cuts) up to 49%. Water continuous regimes with water fractions 90% have the highest efficiency values; thus, these are not affected significantly by crude oil spiking. With crude spiking, the flow regime dispersion of oil in water and water in oil (Dw/o + Do/w) occupies more area in the flow pattern map than unspiked Exxsol D60. It was observed through visual inspection that crude oil spiking induces a thicker and more stable emulsion in higher flow rates (e.g., 700 L/min). Therefore, the spiked mixture needs more time to separate. The findings of this study can help in a better understanding of the applicability of pipe separators and the usage of spiked oils to extrapolate experimental results to real field conditions.Graphical abstract