Single-phase Water Flow Research Articles

Modelling hydraulic jump using the bubbly two-phase flow method

Hydraulic jumps have complex flow structures, characterised by strong turbulence and large air contents. It is difficult to numerically predict the flows. It is necessary to bolster the existing computer models to emphasise the gas phase in hydraulic jumps, and avoid the pitfall of treating the phenomenon as a single-phase water flow. This paper aims to improve predictions of hydraulic jumps as bubbly two-phase flow. We allow for airflow above the free surface and air mass entrained across it. We use the Reynolds-averaged Navier–Stokes equations to describe fluid motion, the volume of fluid method to track the interface, and the k–e model for turbulence closure. A shear layer is shown to form between the bottom jet flow and the upper recirculation flow. The key to success in predicting the jet flow lies in formulating appropriate bottom boundary conditions. The majority of entrained air bubbles are advected downstream through the shear layer. Predictions of the recirculation region’s length and air volume fraction within the layer are validated by available measurements. The predictions show a linear growth of the shear layer. There is strong turbulence at the impingement, and the bulk of the turbulence kinetic energy is advected to the recirculation region via the shear layer. The predicted bottom-shear-stress distribution, with a peak value upstream of the toe of the jump and a decaying trend downstream, is realistic. This paper reveals a significant transient bottom shear stress associated with temporal fluctuations of mainly flow velocity in the jump. The prediction method discussed is useful for modelling hydraulic jumps and advancing the understanding of the complex flow phenomenon.

Imaging water velocity and volume fraction distributions in water continuous multiphase flows using inductive flow tomography and electrical resistance tomography

This paper presents the design and implementation of an inductive flow tomography (IFT) system, employing a multi-electrode electromagnetic flow meter (EMFM) and novel reconstruction techniques, for measuring the local water velocity distribution in water continuous single and multiphase flows. A series of experiments were carried out in vertical-upward and upward-inclined single phase water flows and ‘water continuous’ gas–water and oil–gas–water flows in which the velocity profiles ranged from axisymmetric (single phase and vertical-upward multiphase flows) to highly asymmetric (upward-inclined multiphase flows). Using potential difference measurements obtained from the electrode array of the EMFM, local axial velocity distributions of the continuous water phase were reconstructed using two different IFT reconstruction algorithms denoted RT#1, which assumes that the overall water velocity profile comprises the sum of a series of polynomial velocity components, and RT#2, which is similar to RT#1 but which assumes that the zero’th order velocity component may be replaced by an axisymmetric ‘power law’ velocity distribution. During each experiment, measurement of the local water volume fraction distribution was also made using the well-established technique of electrical resistance tomography (ERT). By integrating the product of the local axial water velocity and the local water volume fraction in the cross section an estimate of the water volumetric flow rate was made which was compared with a reference measurement of the water volumetric flow rate.In vertical upward flows RT#2 was found to give rise to water velocity profiles which are consistent with the previous literature although the profiles obtained in the multiphase flows had relatively higher central velocity peaks than was observed for the single phase profiles. This observation was almost certainly a result of the transfer of axial momentum from the less dense dispersed phases to the water, which occurred preferentially at the pipe centre. For upward inclined multiphase flows RT#1 was found to give rise to water velocity profiles which are more consistent with results in the previous literature than was the case for RT#2—which leads to the tentative conclusion that the upward inclined multiphase flows investigated in the present study did not contain significant axisymmetric velocity components.

An experimental and numerical investigation of the use of liquid flow in serpentine microchannels for microelectronics cooling

This paper presents a combined experimental and numerical investigation of single-phase water flow and heat transfer in serpentine rectangular microchannels embedded in a heated copper block. The performance of four different microchannel heat sink (MCHS) configurations are investigated experimentally, the first having an array of straight rectangular microchannels (SRMs), while the other have single (SPSMs), double (DPSMs) and triple path multi-serpentine rectangular microchannels (TPSMs). Three-dimensional conjugate heat transfer models are developed for both laminar and turbulent single-phase water flows in each of these MCHSs and the governing flow and energy equations solved numerically using finite elements. The numerical predictions of pressure drop (ΔP) and average Nusselt number (Nuavg) are in good agreement with experimental data, and indicated that the single path serpentine microchannel (SPSM) leads to a 35% enhancement of the Nuavg at a volumetric flow rate of 0.5l/min and a 19% reduction in total thermal resistance (Rth) compared to the conventional SRM heat sink. However, this enhancement is at the expense of a large (up to ten-fold) increase in ΔP compared to the SRM heat sink, so that a suitable compromise must be struck between heat transfer and pressure drop in practical MCHS designs.

Fractal analysis of single-phase water and polymer solution flow at high rates in open and horizontally displaced rough fractures

A study on the percolation characteristics of single-phase flow in rough fractures at high rates representing hydraulic fracturing conditions is presented. Two-dimensional transparent models of fractures obtained from different rock types (granite, marble and limestone) were reproduced by molding. To represent typical hydraulic fracturing fluids, water and polymeric solutions were injected at a constant flow rate. The inlet pressure was continuously monitored to correlate the permeability changes due to surface roughness of fractures. The fluid distributions were also mapped using the images acquired through the experiments. The surface roughness was quantified using three fractal methods (variogram, power spectral density, and triangular prism) and the ratio of total and planar areas, and these parameters were correlated to the percent wetted areas and pressure drop (i.e., permeability). This exercise was performed on joint type and horizontally displaced (sheared) model fractures.The percentage of planar flow wetted area representing invasion percolation and pressure drop changed remarkably with rock types. Both parameters were controlled by grain size and the surface roughness of fractures. Increasing degree of the roughness caused a decrease in permeability and area wetted by fluid. Models generated from bigger grain size rocks showed more channeling and a lower percentage of fluid wetted areas as well as lower pressure drop (higher permeability). The variogram fractal dimension showed better agreements among other methods for both fluid (water and polymeric solution) and fracture types (joint and horizontally displaced).

Effects of Airflow Induced by Rainfall on Shallow Groundwater Table Fluctuations.

An investigation of groundwater table fluctuations induced by rainfall should consider interactions between the liquid and gas phases in soils. In this study, a water-air two-phase flow model was initially verified by simulating an infiltration experiment. It was then employed to model the interactions between liquid and gas phases regarding actions of airflow on the groundwater table and the fluctuations of the phreatic level and water level in the well induced by rainfall. The effects of airflo7w caused by rainfall on phreatic level fluctuations were also studied quantitatively by comparing the results obtained using the proposed model with those obtained from a water single-phase flow model. The simulation results show that in addition to actual recharge, compressed airflow in unsaturated zones causes the phreatic level to increase, but the rise in the phreatic level is lower than that in the pore-air pressure head in unsaturated zones due to the mitigation of capillary fringe. The existence of airflow enhances the phreatic level rise during and after rainfall. In addition, the water level in the well, pushed by the phreatic level fluctuations, varies similarly to the phreatic level, but it experiences somewhat delayed and slightly attenuated. The Lisse effect precisely reflects the phreatic level fluctuations before actual recharge. Furthermore, the fluctuations in the phreatic level and water level in the well and the contributions of airflow to phreatic level fluctuations are affected by many factors: rain intensity, initial moisture, overlying aquitard, groundwater table depths, and screen depths of the well.

Evaluation of a new scaling term in preconditioning schemes for computations of compressible cavitating and ventilated flows

This paper presents the application of a dual-time stepping scheme to the computation of unsteady cavitating and ventilated flows. The flows are modeled for multidimensional problems based on fully-compressible multi-component, multi-phase mixture Navier–Stokes equations. In order to handle the sharp discontinuity flows that previously developed preconditioning methods fail to do, the dual-time stepping scheme introduces a modified preconditioning parameter. This preconditioning parameter is defined using a “pressure-based” form so that accurate, efficient, and robust computations can be performed without dependence on the Mach number. The system of equations is solved on multi-block structured curvilinear grids with a high-resolution upwind scheme. Both the convergence performance and validation of the computational results are examined for various test cases including inviscid gaseous mixture flows in a tube, two-phase shock tube problem, free-surface flow in a nozzle, single-phase water flow, cavitating flows, transonic water flow, and ventilated flows over underwater vehicles. The results obtained with the modified form are in good agreement with the exact solutions and experimental data. In terms of accuracy, efficiency, and robustness, the modified form is strongly recommended for use in mixture flow computations when sharp discontinuities are present.

Physical and analytical modelling of permeability damage in bituminous coal caused by fines migration during water production

This study presents a systematic experimental methodology to investigate permeability damage caused by fines migration. The workflow starts with a thorough characterization of a bituminous coal sample by the XRD, SEM-EDX, petrographic, proximate and ultimate methods. Then, a single-phase water flow test is conducted on the coal sample whose surface is covered with Araldite resin to eliminate coal creep. The water permeability is monitored continuously and produced water samples are collected at regular intervals. The produced water samples are tested for conductivity, ionic concentration and fines concentration and sizes. Finally, the produced fines are separated from water using a membrane filter and the fines are examined using the SEM-EDX analysis. The theory of maximum retention function is used to investigate the fines release mechanism.Experimental results indicate a ∼35% decline in coal permeability during 33 days of water flow. The produced fines are mostly coal and coal-clay mixtures, which is different from the observation of Guo et al. (2015) for the anthracite coal where the majority of fines were clay only. Analytical modelling suggests that the major controlling parameters for fines migration during the flow test are the flow rate, interaction energy and coal characteristics. The analytical model also reveals that most of fines are mobilized in the beginning of the flow test.

Hydrodynamic and Thermal Performance of Microchannels With Different In-Line Arrangements of Cylindrical Micropin Fins

This study presents results on the hydrodynamic and thermal characteristics of single-phase water flows inside microchannels (MCs) with different micropin fin (MPF) configurations. Different inline arrangements of micropin fins were considered over Reynolds numbers ranging from 20 to 160. The computational studies were performed using the commercial software ansys 14.5. The hydrodynamic performances of the configurations were compared using two parameters, namely, pressure drop and friction factor while the comparison in their thermal and thermal-hydraulic performances were based on Nusselt number and thermal performance index (TPI). Wake-pin fin interactions were carefully analyzed through streamline patterns in different arrangements and under different flow conditions. The results showed strong dependencies of all four evaluated performance parameters on the vertical pitch ratio (ST/D). Weaker dependencies on height over diameter ratio (H/D), horizontal pitch ratio (SL/D), and minimum available area (Amin) were observed. With an increase in the Reynolds number, extension of the wake regions behind MPFs was observed to be the paramount factor in increasing pressure drop and Nusselt number. Regarding TPI, two adverse trends were observed corresponding to different ST/D ratios, while the effect of SL/D ratio was unique. For friction factors, H/D and SL/D ratios of 1 and 1.5, respectively, led to minimum values, while different ST/D ratios are needed for each diameter size for the maximum performance. Moreover, a twofold increase in Reynolds number resulted in about 40% decrease in friction factor in each configuration.

Rules of pulverized coal output under different components of coal petrography and different coal structure in Hancheng Block, China

In order to study the output mechanism and influencing factors of pulverized coal under different components of coal petrography and different coal structures during the process of drainage, the physical simulation experiments were conducted under the state of single-phase water flow displacement. The results of this experiment for different coal petrography show the weight of pulverized coal output is normally 11# coal > 5# coal > 3# coal with different displacement velocities, and the increasing ratio of pulverized coal output is 5# coal > 11# coal with the different confining stress in the constant displacement velocity. For different coal structures the pulverized coal output weight of fragmented coal is much larger than the primary structure of coal. The particle size distribution curve shows 3#, 5# and 11# primary structure of coal have a double-peak, and the grain size of primary pulverized coal is relatively small and the secondary pulverized coal is relatively large. However, the grain size distribution of fragmented coal is a double-peak distribution, and the distribution scope is relatively concentrated and the average grain size is small. Therefore, the characteristics of pulverized coal were found to be related to its coal different coal petrography components and coal structure.

Stability analysis of unsaturated soil slopes considering water-air flow caused by rainfall infiltration

Even though soil is a mixture of solids with voids that are filled by air and water, most previous studies on rainfall infiltration and its influence on slope stability were based on a single-phase water flow model by assuming that the pore air pressure was atmospheric. The purpose of this study is to examine the effect of interactions between air and water flow due to heavy rainfall on the mechanical stability of an unsaturated soil slope. Water-air two-phase flow analyses were conducted to investigate the contribution of pore-air pressure on infiltration by rainfall. In order to study the infiltration behavior with respect to soil type, flow analyses were performed with two types of soil under similar settings. Results obtained from the two-phase infiltration analysis were then used as input to the stability analysis by the strength reduction method. Infiltration and stability analyses based on a single-phase water flow model were also carried out, which helped clarify the effects of air flow induced by rainfall infiltration on an unsaturated soil slope. The results showed an increase in pore air pressure during infiltration because rainwater displaced the air in the unsaturated zone; hence, remarkable delaying effects on water flow were induced. Such water-air interactions in the pore space of soil significantly affected the stability and behavior of the soil slope.

Experimental hydrodynamic study of flow through metallic foams: Flow regime transitions and surface roughness influence

The aim of the present work is to study the hydrodynamic behavior of the single phase water flow through three metallic foam samples (i.e. Copper, NiFeAlC, and Inconel) in a plate heat exchanger. These samples have a same pore diameter (1200 µm) and grade (20 PPI), however, the Microscopic images show that the ligament diameter and the surface roughness are different. The effect of the metallic foam surface roughness and the ligament diameter on the pressure drop behavior is analyzed, and the regime transitions from pre-Darcy to turbulent are identified. It is found that more, the metallic foam surface is rough, more the pressure drop is important and the turbulent regime is reached rapidly. The Permeability and Forchheimer parameters were calculated for each flow regime. It is noticed that each fluid regime can exhibit different permeability and Forchheimer coefficient for the same foam sample. The present data were confronted to those available in the literature and a good qualitative and quantitative agreement was obtained.

Hydrodynamics of two-phase flow in a rod bundle under cross-flow condition

Pressure drop experiments were conducted for a vertical two-phase air–water flow across a horizontal staggered rod bundle under conditions of air quality ranging from 0.001 to 0.3 and mass velocity ranging from 80 to 500kg/(m2s). The experimental data were thoroughly analyzed and compared with predictions from existing correlations. New developed expressions provided the most accurate predictions. The two-phase friction multipliers for G⩽200kg/(m2s), which show a strong mass velocity effect, could be fit well in terms of the Martinelli parameter and the dimensionless mass velocity. The new correlation developed for the two-phase friction multiplier was successfully tested in predicting the experimental data for G⩽200kg/(m2s) in previous experiments of other researchers. Distributions of velocity and turbulent intensity were also obtained from the numerical simulation on single-phase flow of water using the CFD code ANSYS FLUENT 14.0. The SST k–ω model was verified to be the best turbulent model to gain flow characteristics in the horizontal rod bundle under experimental conditions.

A semi-analytical method for forecasting wells completed in low permeability, undersaturated CBM reservoirs

Exploration and development of coalbed methane (CBM) reservoirs is ongoing in the Asia Pacific region, with low permeability, undersaturated coals being the target in some areas. Horizontal wells are typically required to produce low permeability CBM reservoirs at commercial rates, and may experience a period of single-phase (water) transient flow, followed by a transition to two-phase (water + gas) transient flow. Wells exhibiting this behavior are particularly difficult to model analytically, yet simple analytical and semi-analytical tools are desirable for making quick, but reasonably accurate forecasts. The purpose of this work is to therefore provide a new forecasting methodology for low permeability, undersaturated CBM wells.The new method for forecasting CBM wells introduced in this work is based on the concept of a dynamic drainage area (DDA), recently adapted to forecast tight black oil and gas condensate wells exhibiting two-phase flow. A critical advancement provided in the current work is modeling the transition from single-phase flow of water to two-phase flow of gas and water during the transient linear flow period, which was not attempted for the black oil/gas condensate cases. Above desorption pressure, material balance, performed on the dynamic drainage area to determine average pressure in the distance of investigation, is combined with the linear flow productivity index equation to forecast water production at each time step. For two-phase flow below desorption pressure, the two-phase version of the linear productivity equation and material balance equations for water and gas are solved iteratively for pressure, saturation and fluid production rate within the DDA. The gas material balance equation accounts for desorption effects. In order to calculate the DDA at each time step, the linear flow distance of investigation equation is used. Importantly, using the DDA method, variable operating conditions (flowing pressures) may be accounted for, which is critical for CBM wells during early stages of production.The new semi-analytical DDA model is used to history-match production data from an actual horizontal well completed in a low permeability, undersaturated, western Canadian CBM reservoir. Further, the match is compared to that obtained from rigorous numerical simulation. The history-match of the field data is reasonable with the new model and comparable to numerical simulation. The new model is however easier to setup and less data-intensive than numerical simulation, providing a practical alternative to CBM reservoir engineers who are responsible for generating a large number of forecasts.

Flow-Accelerated Corrosion in Pipe Wall Downstream of Orifice for Water and Air-Water Bubble Flows

An orifice is used widely as a flow meter or a contraction device in pipeline systems in hydro-power plants, thermal power plants, and chemical plants because of its simple construction, high reliability, and low cost. However, it is well known that flow-accelerated corrosion (FAC) occurs on the pipe wall downstream of the orifice. Some of the authors have examined FAC through experimental and numerical analyses and have reported that one of the major governing parameters of FAC for single-phase water flow is the pressure fluctuation p’ on the pipe wall, and also that pipe wall thinning rate TR can be estimated by p’. In addition, they have presented the effects of the ori-fice geometry on p’ or TR, and have described a method for suppressing p’ or TR. In the present study, FAC for a two-phase air-water bubble flow is examined and compared with the single-phase water flow experimentally. Further, it is shown that because p’ is also considered a governing parameter of FAC for a two-phase air-water bubble flow, TR can be estimated using p’. It is also indicated that, by using a downstream pipe with a smaller diameter than that of the upstream pipe, p’ or TR can be suppressed.

2상 흐름모델에 의한 강우침투를 고려한 불포화 토사 사면의 안정해석

Most previous studies on the rainfall infiltration and its influence on slope stability were based on the single-phase water flow model. The purpose of this study is to study the effect of interaction of air and water flow on the slope stability. In this study, two-phase flow analyses were conducted for weathered residual soil slopes with thin soil overlying impermeable bedrock. Results of the flow analysis were used as input for stability analysis by strength reduction method. Strength reduction method considers mechanical equilibrium to evaluate the effect of rainfall infiltration on the slope stability. The results show that remarkable delaying effects by air flow on the propagation of the wetting front and the deterioration of slope when surface ponding occurs during infiltration. On the other hand, the influence of the pore air flow on the slope stability can be neglected in the non-ponding situation with small rainfall intensity.

Transient flow analysis and partial water relative permeability curve derivation for low permeability undersaturated coalbed methane wells

Rate transient analysis (RTA) is an important reservoir engineering tool used to extract reservoir and stimulation information from flow rates and pressures obtained from producing wells. Adaptation of analytical RTA methods for this purpose has been slow for coalbed methane (CBM) reservoirs because of the complexities of multi-phase flow, non-static absolute permeability, desorption, among others. Some progress has been made historically for high permeability CBM reservoirs, where depletion (boundary-dominated flow) occurs quickly, however low permeability CBM reservoirs are currently being evaluated internationally (e.g. China), which brings forward additional challenges. For example, in some instances, low permeability, undersaturated CBM wells exhibit long periods of transient flow, during which the transition from single-phase flow of water to two-phase flow of gas and water occurs. This behavior has not been dealt with rigorously in the development of analytical RTA methods. It is the purpose of the current work to extend RTA to apply to low-permeability, undersaturated CBM wells exhibiting this behavior.The horizontal CBM well studied in this work exhibits two periods of apparent transient linear flow separated by a transition, as determined from diagnostic analysis of water production data using a log–log plot of rate-normalized pressure (RNP) versus time. It is hypothesized that the well actually exhibits transient linear flow throughout the entire studied production period (supported by reservoir simulation) and that productivity changes leading to the apparent transition in flow regime are caused by the combined effects of relative permeability changes after desorption pressure is reached, and (possibly) fines migration and stress-dependent permeability. In order to extend the early single-phase linear flow analysis of this well (occurring above desorption pressure) to the multi-phase period (below desorption pressure), the RNP half-slope trend (linear flow) established during the single-phase flow period is extrapolated through the rest of the production period. An RNP ratio (RNPR) is then created by calculating the ratio of the extrapolated (corrected) RNP and the RNP of the uncorrected field data. The RNPR can then serve to correct the production data affected by multi-phase flow (and possibly fines migration and stress dependent permeability) and hence extend the amount of data that can be used for production analysis. Further, the RNPR squared, combined with water saturation calculations, may be used to derive water relative permeability curves from the transient data. These concepts are tested using both numerical simulation and field data. The resulting field-derived water relative permeability curve can be used as a solid starting point for simulation history-matching, although it covers a limited range of water saturations.This work should be of interest to professional engineers and geoscientists involved in CBM reservoir characterization efforts. Future work will determine if these concepts are applicable to other low-permeability reservoirs exhibiting the transition from single- to multi-phase flow during the transient linear flow period, such as tight oil and gas condensate reservoirs.

Effect of drops on turbulence of kerosene–water two-phase flow in vertical pipe

The effect of introducing kerosene drops on turbulence of kerosene–water two-phase in a vertical pipe is investigated experimentally. A hot-film and dual optical probes are used to measure the water velocity, turbulence fluctuation, drop relative velocity, volume fraction and drop diameter. Experiments are performed in a 78.8mm diameter vertical pipe for four average water velocities of 0.11, 0.29, 0.44 and 0.77m/s. The measurements were carried out for two area average volume fraction 〈α〉 of 4.6% and 9.2% as well as for water single phase flow to investigate the effect of introducing kerosene drops on two-phase flow turbulence. The kerosene–water mixture was generated by adding the kerosene to constant flow rates of water. The results indicate that drops induced turbulence is a function of the ratio of the drop Reynolds number (UrdB/ν) to the turbulence Reynolds number (u′Lt/ν) which decreased with higher water velocities. The results show that the Kolmogorov–Richardson scaling in the range of −4.5/3 to −6/3 for single phase flow which is replaced by −6/3 to −7/3 for two-phase flow. These values are less than −8/3 for air–water flow.

Experimental study of transient behaviour of laminar flow in zigzag semi-circular microchannels

An experimental investigation is carried out to understand the hydrodynamics of single-phase water flow in a zigzag microchannel with a semi-circular cross-section (diameter 2mm). The present study covers Reynolds numbers in the laminar regime, under both steady and transient conditions. Time-resolved velocity measurements were made using high-speed micro-PIV techniques. The influence of inlet unsteadiness on flow characteristics is investigated. Through time-resolved velocity measurements, a transition from a steady flow to a time-dependent oscillatory flow having a few dominant frequencies and subsequently to a complex transient flow is observed in the wavy channel. However, the transition to a transient flow occurs at much lower Reynolds numbers (Rec∼215) than predicted numerically. The early transition is believed to be triggered by small inlet flow disturbances in the experiments, since the flow is very sensitive to the inlet conditions at sufficiently high Reynolds numbers. This hypothesis is supported by results from transient CFD simulations with fluctuating inlet boundary conditions.

The Effect of Micro Pin-Fin Shape on Thermal and Hydraulic Performance of Micro Pin-Fin Heat Sinks

Single micro pin-fin configurations having the same chord thickness/diameter but different shapes are numerically modeled to assess their heat transfer and hydraulic performances for Reynolds number values changing between 20 and 120. The configurations are three-dimensionally modeled based, and their heat transfer performances are evaluated using commercially available software COMSOL Multiphysics 3.5a. Navier–Stokes equations and continuity and energy equations are solved under steady-state conditions for single-phase water flows. To increase the computational efficiency, half of the domain consisting of a micro pin-fin located inside a microchannel is modeled using a symmetry plane. To validate the model, experimental data available in the literature are compared to simulation results obtained from the model of the same geometrical configuration as the experimental one. Accordingly, the numerical and experimental results show good agreement. Furthermore, performance evaluation study is performed using three-dimensional (3D) numerical models in the light of flow morphologies around micro pin-fins of various shapes. According to the results obtained from this study, the rectangular-shaped micro pin-fin configuration has the highest Nusselt number and friction factor over the whole Reynolds number range. However, the cone-shaped micro pin-fin configuration has the best thermal performance index, indicating that it could be more preferable to use micro pin-fins of unconventional shapes in micro pin-fin heat sinks.

Effect of drag reducing polymer on horizontal liquid–liquid flows

The effect of adding a drag reducing polymer in the water phase during horizontal oil–water flows was studied experimentally. Experiments were carried out in a 14mm ID acrylic pipe using tap water and kerosene oil (Exxsol D140: density 828kg/m3; viscosity 5.5mPas at 23°C) as test fluids. An initial master solution of the polymer (Magnafloc 1011, a copolymer of polyacrylamide and sodium acrylate) at 1000ppm concentration was added at different flowrates into the water phase to give polymer concentrations in the test section between 2.5 and 50ppm. Flow patterns were investigated with high speed imaging while conductivity probes were used to obtain interface properties in separated flows. It was found that as little as 20ppm polymer in the water phase could give maximum drag reduction of about 45% during two-phase flow. When polymer was added, the region of stratified oil–water flow extended to higher superficial oil and water velocities. In separated flows, the polymer addition resulted in a decrease in the interface height and increase in average water velocity. In addition, interfacial wave amplitudes decreased while wave lengths and celerities increased. Velocity measurements in single phase water flows with particle image velocimetry showed that the addition of polymer changed the axial velocity profile and decreased the Reynolds stresses to almost zero values.