High Mixture Velocities Research Articles

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.

Effect of mixture velocity for given equivalence ratio on flame development in Swiss roll combustor

Small-scale power generation using heat energy from hydrocarbon fuels is a proven technology. In this study, we analyzed 2-D flame development in meso-scale Swiss roll combustor. A mixture of 60% butane and 40% propane was used (0.25?0.55 L per minute). During all the analyses, equivalence ratio (1.1) was kept constant by adjusting air quantity against fuel quantity. The effect of increase in the mixture velocity on the development of flame shapes/patterns was monitored. We found different patterns of flame, e. g., planar, concave, and conical, with the increase in mixture velocity. Increase in combustion chamber temperature was also noted. No flashback was observed and blowout was observed with very high mixture velocity. Combustion chamber temperatures were found to be increasing with the increase in mixture velocity at the same equivalence ratio. Elongation of the flame was observed because of the increased flow velocity. Heat re-circulation to the reactants enhances flame characteristics.

Large-Scale Experiments on Slug-Length Evolution in Long Pipes

Summary We present a unique set of two- and three-phase slug-flow experiments conducted in a 766-m-long, 8-in. pipe at 45-bara pressure, using Exxsol™ D60 fluid (ExxonMobil Chemical, Houston, Texas, USA) as the oil phase and nitrogen as the gas phase. The first one-half of the pipe was horizontal, while the second one-half was inclined by 0.5°. A total of 10 narrow-beam gamma densitometers were mounted on the pipe to study flow evolution, and in particular slug-length development. The results show that the mean slug length initially increases with the distance from the inlet, but this increase slows down, and the mean slug length typically reaches a value between 20 and 50 diameters at the outlet. At low mixture velocities (<3 m/s), the slug-length distributions tend to be extremely wide, sometimes with standard deviations approaching 100%. The longest slugs that we observed were more than 250 pipe diameters (50 m). At higher mixture velocities (>3 m/s), the slug-length distributions are in general narrower. The effect of the water cut (WC) on the slug-length distribution is significant but complex, and it is difficult to establish any general trends regarding this relationship. Finally, it was observed that slug flow often requires a very long distance to develop. Specifically, in most of the slug-flow experiments, the flow regime 57 m downstream of the start of the horizontal section was not slug flow.

Effects of flow rate and fuel/air ratio on propagation behaviors of diffusion H2/air flames in a micro-combustor

A Y-shaped micro combustor consisting of three quartz tubes with an identical inner diameter of 2.0 mm was designed. Effects of total flow rate and fuel/air ratio on the propagation behaviors of non-premixed hydrogen-air flames were investigated experimentally. Six distinct modes were observed, including flames with repetitive extinction and ignition. Noise emission was detected during flame propagation towards upstream under relatively high mixture velocities. The mean flame propagation speed decreased monotonically with an increasing mixture velocity, however, it exhibited a non-monotonic variation with the nominal equivalence ratio and peaked at ϕ = 0.9. Stable edge flames were obtained at the intersection under suitable conditions, and its length increased as the mixture velocity was increased, but varied non-monotonically with the nominal equivalence ratio and had a maximum value at ϕ = 0.9. The regime diagram of the six flame propagation modes was drawn, which can provide an overview of the relationship between the inlet condition and flame propagation mode. Qualitative analysis showed that flame dynamics of non-premixed micro-combustion was closely associated with the total flow rate and fuel/air ratio by influencing the mixing effectiveness, residence time, heat release rate and heat loss rate.

Measurement of local oil holdup for oil-in-water emulsion flows using multiple mini-conductance probes

In the present work, local oil holdup in oil-in-water emulsion flows is experimentally investigated with multiple mini-conductance probes. With the aid of finite element method (FEM), we firstly optimize the geometry structure of a mono-sensor conductance probe through the examination on its electrical and sensitivity field distribution. Thereafter, multiple mini-conductance probes composed by 16 mono-sensor probes are designed for a vertical upward pipe with 20 mm inner diameter (ID). The flow conditions regarding pipeline flows of oil-in-water emulsion are set within low velocity (0.0184–0.2576 m/s) and high water-cut (80–96%). By processing the fluctuating signals of multiple mini-conductance probes, we derive oil holdups on different positions at pipe cross section. Accordingly, oil holdup distribution at the whole pipe cross section is acquired using cubic spline interpolation, and correspondingly the slippage effect between oil and water phase is analyzed. The research results indicate that local oil holdup distribution is susceptible to the variation in mixture velocity and water-cut. Furthermore, the degree of inhomogeneous distribution in local oil holdup presents the weakest under the conditions of high mixture velocities as well as high water-cuts. Finally, a complexity measure designated as weighted-permutation entropy is extracted from the fluctuating signals of multiple mini-conductance probes to characterize the evolution in oil holdup distribution from the perspective of nonlinear dynamics.

Effect of pipe diameter on horizontal oil-water flow before and after addition of drag-reducing polymer part II: Holdup and slip ratio

In this experimental work, the effect of the drag-reducing polymer on the holdup and slip ratio of the oil-water flow in three different horizontal acrylic pipes was investigated. The internal diameters (IDs) of the pipes were 30.6-mm, 55.7-mm and 74.7-mm. The flow conditions of the oil-water flow consisted of 0.4–1.6 m/s mixture velocities and 0.1–0.9 input oil volume fractions. The master solution of the polymer (commercially known as AN 105-SH) was prepared at 2000 ppm concentration and injected into the water phase at controlled flow rates to provide 40 ppm concentration in the phase. The measurement of the holdup was carried out with help of quick closing valves after which the slip ratio was determined. The results showed that the water holdup and by extension, the slip ratio before the addition of the DRP increased with increase in the input oil volume fraction at low mixture velocity while the reverse was the case at high mixture velocity. The addition of the DRP increased the water holdup and the slip ratio only in water-dominated flow regions in all the three pipes. Finally, the increase in the pipe diameter also increased the water holdup and the slip ratio before and after the addition of the DRP in most of the flow conditions.

Effect of Surfactant Additives on Phase Inversion in Oil-Water Pipe Flow System

This research investigates the effect of surfactant additives on phase inversion point in the oil-water flow in horizontal pipe. Two types of surfactants were used in the experiments; anionic type (sodium lignosulfonate (SLS)) at 200 ppm and cationic type (hexadecyltrimethyl ammonium bromide (CTAB)) at 100 ppm. The experiments were carried at mixture velocities (0.8, 1, 1.9 and 2.3) m/s. The results showed that the phase inversion points are unaffected by surfactant addition or velocity at low mixture velocities while they shifted downward at high mixture velocities. The experiments show also that anionic surfactant addition caused a forward shifting in phase inversion point and downward shifting in the addition of cationic surfactant at high mixture velocities.

Effect of pipe inclination on holdups/velocity ratios of oil-water flow without and with addition of drag-reducing polymer

In petroleum industries, the demand for effective design and operation of the oil-water transport systems is very high, and holdup of each phase is one of the important hydrodynamic parameters needed for such design and operation. This parameter can be affected by several factors one of which is the presence of the drag-reducing polymers in the oil-water flow. Therefore, the focus of this experimental study is on the effect of the drag-reducing polymer on the holdups and by extension, velocity ratios of the oil-water flow. Specifically, the investigation of the holdups and velocity ratios of the oil-water flow before and after the addition of the drag-reducing polymer was carried out in horizontal (0ᴼ) and different inclined (−5ᴼ, +5ᴼ and +10ᴼ) acrylic pipe with 30.6-mm ID. The investigation was conducted using flow conditions of 0.4, 0.8 and 1.6m/s mixture velocities and 0.1–0.9 input oil volume fractions at each inclination. In each experimental run, the holdup of each phase was measured after steady flow was achieved using quick closing valves. Thereafter, the master solution of the polymer which was prepared at 2000ppm water was injected at controlled flow rates to provide 40ppm of the polymer in the water phase and the measurement was repeated. It was found generally that the water holdups and hence, the velocity ratios were increased after the addition of the polymer particularly in water-dominated flow regions. The velocity ratios also increased with the increase in the mixture velocities at these same flow regions. Finally, water was found to flow faster for separated flow at 0.4m/s while for the dispersed flow regions at higher mixture velocities, the dispersed phase was in general the faster flowing phase.

Flow structure and pressure gradient of extra heavy crude oil-water two-phase flow

The flow structure and pressure gradient of extra heavy crude oil (viscosity=11232.8mPa·s at 50°C) and water two-phase flow were studied in a horizontal flow loop with 25.8mm inner diameter and overall length of 30.8m. With the help of high-speed photography, local sampling and pressure gradient testing, six different flow patterns were identified. A new flow pattern—discrete water-in-oil emulsion and water annular flow (Ew/o&w dispersion-annular flow)—was found at high water fractions and high mixture velocities. The size distribution of water droplets in Ew/o flow and the periodic characteristics of Ew/o&w intermittent flow were analyzed in detail. Relative pressure gradient was introduced to characterize the oil-water two-phase flow. The pressure gradients of water dominated flow are two orders of magnitude lower than that of oil dominated flow. The water fraction and temperature have little effect on the pressure gradient of water dominated flow, particularly in annular flow. The water dominated flow should be given priority to when it comes to the transportation of extra heavy crude oil and water. The results establish a theoretical basis for water-lubricated transport of extra heavy crude oil.

A comprehensive deposition velocity model for slurry transport in horizontal pipelines

Transportation of solids in form of slurries has become one of the most important unit operations in industries across several disciplines. In fact, the need is more pronounced in industries that are very important for human survival such as food processing, pharmaceuticals and energy (coal, oil and gas). A lot of work has been done in the past 30 years in understanding the factors affecting the deposition velocity of solids in slurries. Experimental observation and theoretical predictions pointed to mixture velocity and solid/fluid properties especially rheology of the resulting slurry to be the most important factors that dramatically affect particle motion and patterning. This paper presents a critical deposition velocity model and a “stability flow map” for complex rheology slurries. The critical deposition model utilizes a more robust generalized two-parameter rheology model to account for any given slurry rheology. The “stability flow map” demarcates the different flow patterns that may be observed at different mixture velocities and rheologies. On this map, the homogeneous slurries are predicted at low rheology and high mixture velocity, whereas heterogeneous slurries (with a concentration gradient) predicted at high rheology (yield stress effects). Sensitivity analysis was conducted on critical Reynolds number, particle density, carrier fluid density, generalized flow behavior index and pipe diameter. It was observed that increase in shear thinning behavior, particle density, pipe diameter and particle diameter led to a decrease in the laminar region and an increased unstable region. The model showed good performance when tested on glass and stainless steel beads test data available in open literature. Preliminary simulation with this map may help engineers select flowline size and carrier fluid rheology for a given type of solid particle.

Effect of Water-Soluble Drag-Reducing Polymer on Flow Patterns and Pressure Gradients of Oil/Water Flow in Horizontal and Upward-Inclined Pipes

Summary Experimental investigations of flow patterns and pressure gradients of oil/water flow with and without drag-reducing polymer (DRP) were carried out in horizontal and upward-inclined acrylic pipe of 30.6-mm inner diameter (ID). The oil/water flow conditions of 0.1- to 1.6-m/s mixture velocities and 0.05–0.9 input oil-volume fractions were used, and 2,000 ppm master solution of the water-soluble DRP was prepared and injected at controlled flow rates to provide 40 ppm of the DRP in the water phase at the test section. The flow patterns at the water-continuous flows were affected by the DRP, whereas there were no tangible effects of the DRP at the oil-continuous flow regions. The upward inclinations shifted the boundaries between stratified flows and dual continuous flows, and the boundaries between dual continuous flows and water-continuous flows to lower mixture velocities. This means that the inclinations increased the rate of dispersions. The frictional pressure gradients for both with and without DRP slightly decreased with inclinations especially at low mixture velocities, whereas the significant increases in the total pressure gradients with the inclinations were more pronounced at low mixture velocities. The inclinations did not have a major effect on the drag reductions by the DRP at the high mixture velocities and low-input oil-volume fractions where the highest drag reductions recorded were 64% at 0° inclination and 62% at both + 5° and +10° inclinations. However, the inclinations increased the drag reductions as the input oil-volume fractions were increased before phase-inversion points.

Experimental investigation of two-phase water–oil flow pressure drop in inclined pipes

In this experimental work the effect of inclination on the pressure gradient in two phase oil–water flow is investigated. The experiments were performed in a 6m long, 20mm inner diameter and inclinable acrylic pipe using oil (3mPas viscosity and 830kg/m3 density) and water (1mPas viscosity and 990kg/m3 density) as test fluids. Pressure gradients between inlet and outlet of flow in pipe were measured for inclination angles of 0°, ±5°, ±15°, ±30° and ±45° with respect to the horizontal plane. The experimental results were compared with Homogeneous and Two-Fluid models. It was observed that in high mixture velocities, where dispersed flow prevails, there is a peak pressure gradient which is related to phase inversion. It was also found that, phase inversion appears at higher inlet water cut values in inclinations of −30° and −45° compared with other inclinations. However the two-fluid model and homogeneous model both over-predicted the pressure drop, but two-fluid model predicted the pressure drop with less average deviation. Several correlations for effective mixture viscosity in a homogeneous model were considered and the results were compared with experimental results. Acceptable agreement was seen between the computed and measured data.The experimental two-phase friction factors were compared with the friction factors for single phase flow of oil and water, at the same velocities as the two phase mixture and it was found that the experimental friction factors were less than the predicted friction factors of single phase flow.

Effect of low interfacial tension on flow patterns, pressure gradients and holdups of medium-viscosity oil/water flow in horizontal pipe

In most cited literatures, low-viscosity oils (1–10cP) or high-viscosity oils (greater than 100cP), which formed interfacial tension (IFT) of not less than 20mN/m with water were used in determining the characteristics of oil–water flows and very few studies used medium-viscosity and low-forming IFT oils. Therefore, this experimental study was carried out to investigate the flow characteristics such as pressure gradients, flow patterns and holdups/velocity ratios of medium viscosity oil/water flow with low IFT in horizontal pipe of 30.6mm-ID. The medium viscosity oil is a mineral oil with viscosity and density of about 24cP and 872kgm−3 respectively at 25°C. Measurement of the flow characteristics covered the range of mixture velocities from 0.1 to 1.5m/s and input oil volume fractions from 0.1 to 0.9. Pressure gradients were found to increase with increase in mixture velocities and input oil fractions. Phase inversions were observed at mixture velocity as low as 0.6m/s where there were sharp increase in the pressure gradients and the phase inversion points occurred between 0.55 and 0.6 input oil fractions for the whole range of flow conditions. In addition, all the flow patterns identified using visual observation and high speed video camera can be grouped into three categories – stratified, dual continuous and dispersed flow. In terms of mixture velocity, the stratified flow was observed up to 0.2m/s, the dual continuous flow was between 0.2 and 0.5m/s and the dispersed flow was observed from 0.6m/s and above. The velocity ratios were found to increase with increase in mixture velocity except at high input oil fractions where oil was the continuous phase. It was also observed that water was the faster flowing phase at low and medium mixture velocities while the reverse was the case at high mixture velocity. Lastly, the results of the study were compared with existing results from previous works which used medium-viscosity but high-forming IFT oils.

Pressure drop and gas holdup in air–water flow in 180° return bends

Gas–liquid flows in curved tubes are found in a number of applications, such as heat exchangers and transport pipes. The present work deals with air–water flow in 180° tube bends (curvatures of 6.1, 8.7, and 12.2) that connect two 5-m long 26-mm ID horizontal tubes. The bend lies in the vertical position and the two-phase flow can be set as upward or downward. The straight and curved segments of test section were made from borosilicate glass to enable visual access to the two-phase flow. The behavior of the static pressure upstream and downstream of the bend was measured for a wide range of flow conditions, covering the stratified, intermittent and annular flow patterns. The pressure drop and gas holdup change associated with the bend were measured for both upward and downward flows, enabling the calculation of the frictional, accelarational and gravitational components of the total pressure drop in the bend. The distribution of the phases in the bend was investigated with a high-speed camera, revealing several two-phase phenomena responsible for large variations in gas holdup between the inlet and outlet of the bend for both upward and downward flows. An assessment of the prediction methods currently available in the literature showed that correlations for gas holdup in straight tubes give inaccurate predictions of the average gas holdup in the bend for both flow orientations. Frictional pressure drop correlations for gas–liquid flows in return bends also failed to describe with reasonable accuracy the behavior of the experimental data at low gas superficial velocities for both flow orientations. The performance of the correlations improved at high mixture velocities.

A Study of Pressure Gradient Characteristics of Oil-Water Dispersed Flow in Horizontal Pipe

The behavior of oil/water dispersed flow is one of the oil/water two phase flow phenomena encountered in pipeline operations commonly. Due to the different operation conditions, kinds of flow patterns (O/W and W/O) can be observed, as well as the phase inversion point. Pressure gradient characteristics of the three flows vary greatly. Pressure gradients at phase inversion point are higher than those under other conditions which pose great harm to pipeline operations. Three oil samples of different viscosities were used in this study. Mixture flowrate, oil content and mixture temperature data were obtained for oil-water tests. Data analysis shows that pressure gradients exist 3 different stages as oil content changed (O/W stage, phase inversion stage and W/O stage). Pressure gradient characteristics behave differently during the 3 stages. The viscosity of the continuous phase is the dominant factor affecting pressure gradients and droplet size and number also play a role. High mixture velocity will promote pressure gradients. Mixture velocity also affects the viscosity of the working fluid. High velocity lowers apparent viscosity and decreases pressure gradients. The increment rate of pressure gradients can slow down with the increase of mixture velocity. Mixture temperature mainly affects the viscosity of the continuous phase and creats tiny effect on the dispersed phase. High temperature lowers the viscosity of the continuous phase and decreases the pressure gradients.

Investigation on heavy crude-water two phase flow and related flow characteristics

In this paper, heavy crude oil–water flows are studied in a horizontal stainless steel test section with 25.4 mm ID and overall length of 50 m. Crude oil (viscosity = 628.1 mPa s, interfacial tension with water = 10.33 mN/m at 60 °C) and water, collected from an oilfield, were used as test fluids. Visual observations, local sampling and pressure drop measurements were used to identify the flow patterns and their transitions. It was found that in all conditions studied there was a water-in-oil emulsion present. At low mixture velocities and water fractions this occupied the whole pipe cross section. As the velocity or the volume fraction increased water appeared to segregate. At high water fractions and mixture velocities annular flow appeared with the water-in-oil emulsion in the core surrounded by a water layer. The results were compared with those from a model oil with the same viscosity. At low water fractions there was a similarity between the patterns observed with the two oil systems characterized by water segregation from an oil continuous dispersion with increasing water fraction or mixture velocity. However, at high water fractions an oil-in-water dispersion formed with the model oil that was not seen with the crude oil. Pressure drop was generally higher for the crude oil system compared to the model one, while in both cases it decreased when water started to segregate and form layers in contact with the pipe wall. The differences between the two oil systems are attributed to the natural surfactants present in the heavy crude oil (such as asphaltenes and resins), which tend to accumulate on the water/oil interface, retard film drainage and maintain the stability of water drops in oil.

Heat transfer in well-characterised Taylor flow

The flow and heat transfer behaviours of gas–liquid, non-boiling, Taylor flow in the vertical upward direction were studied experimentally using a 2.00 mm diameter channel. Nitrogen and water at atmospheric pressure were employed as the working fluids. Three circular T-junction mixers with different diameters were used to generate gas bubbles and liquid slugs of different lengths (1–220 d) with controlled mixture velocities (0.11< U TP <0.53 m s −1, 200< Re TP <1100) and homogeneous void fractions (0.03< β<0.90). High-speed visualization of adiabatic flow and heat transfer rate determination for constant wall heat flux conditions were performed. The heat transfer enhancement brought about by Taylor flow is found to be larger with shorter slugs and higher mixture velocities. An enhancement up to 3.2-fold over the liquid-only flow was observed. Based on the experimental data, a correlation between the apparent slug Nusselt number ( Nu L⁎ ) with a Graetz number, where the characteristic length is that of the slug, is proposed.

Experimental studies on phase inversion in a small diameter horizontal pipe

The present work describes phase inversion during kerosene–water flow through a 0.012 m diameter horizontal pipe. The phenomenon has been identified using three techniques namely the optical probe technique, pressure drop measurements and an isokinetic sampling technique. Since repeated experiments have reveled dispersed flow to occur at high mixture velocities (>1 m/s), the studies have been conducted for mixer velocity ranging from 1 m/s to 2.5 m/s. The observations have shown that the transition from oil-in-water to water-in-oil dispersion occurs via an emulsified homogenous mixture at high mixture velocities while several different flow patterns mark the transition at lower flow rates of the two phases.

Comparison of Particle Image Velocimetry and Laser Doppler Anemometry measurement methods applied to the oil–water flow in horizontal pipe

In this work, a comparison of Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA) measurement methods was made applied to oil–water two-phase flow in a horizontal pipe. The experiments were conducted in a 15 m long, 56 mm diameter stainless steel pipe using Exxsol D60 oil (density 790 kg/m 3 and viscosity 1.64 mPa s) and water (density 996 kg/m 3 and viscosity 1.0 mPa s) as test fluids. The experiments were performed at different mixture velocities and water cuts. Mixture velocity and water cut vary up to 1.06 m/s and 0.75, respectively. The instantaneous local velocities were measured using PIV and LDA, and based on the instantaneous local velocities mean velocities and turbulence profiles are estimated. The measurements are performed in the vertical plane through the pipe center. A double-pulsed Nd:yttrium aluminium garnet (YAG) laser and a high-speed camera with 1260×1024 px resolution (1.3 Mpx) were used for the PIV measurements. The LDA set-up is a two-colour backscatter system with 3 W Argon-Ion Laser. The time averaged cross-sectional distributions of oil and water phases were measured with a traversable gamma densitometer. The measured mean axial velocity and turbulence profiles using PIV were observed to compare favourably well with LDA measurements. Nevertheless, the PIV measurements are more sensitive for optical disturbances in the dispersed region close to the oil–water interface. Hence, this region cannot be confidently analyzed using PIV, whereas LDA offers full-field measurements even at higher mixture velocities.

Effect of drag reducing polymers on oil–water flow in a horizontal pipe

Measurements of drag-reduction are presented for oil–water flowing in a horizontal 0.0254 m pipe. Different oil–water configurations were observed. The injection of water soluble polymer solution (PDRA) in some cases produced drag reduction of about 65% with concentration of only 10–15 ppm. The results showed a significant reduction in pressure gradient due to PDRA especially at high mixture velocity which was accompanied by a clear change in the flow pattern. Phase inversion point in dispersed flow regime occurred at a water fraction range of (0.33–0.35) indicated by its pressure drop peak which was disappeared by injecting only 5 ppm (weight basis) of PDRA. Effect of PDRA concentration and molecular weight on flow patterns and pressure drops are presented in this study. Influence of salt content in the water phase on the performance of PDRA is also examined in this paper.