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

AbstractThe present study is a report on the asymmetry of dispersed oil phase in vertical upward oil-water two phase flow. The multi-channel signals of the rotating electric field conductance sensor with eight electrodes are collected in a 20-mm inner diameter pipe, and typical images of low pattern are captured using a high speed camera. With the multi-channel rotating electric field conductance signals collected at pipe cross section, multi-scale time asymmetry (MSA) and an algorithm of multi-scale first-order difference scatter plot are employed to uncover the fluid dynamics of oil-water two phase flow. The results indicate that MSA can characterise the non-linear behaviours of oil-water two phase flow. Besides, the MSA analysis also beneficial for understanding the underlying inhomogeneous distribution of the flow pattern in different directions at pipe cross section.

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Application of Thermal Sensors for Determination of Mass Flow Rate and Velocity of Flow in Pipes of Hermetic Systems

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.826.117 ◽

2019 ◽

Vol 826 ◽

pp. 117-124

Author(s):

Yurii Baidak ◽

Iryna Vereitina

Keyword(s):

Temperature Distribution ◽

Mass Flow Rate ◽

Cross Section ◽

Correction Factor ◽

Mass Flow ◽

Flow Rate ◽

Thermal Sensors ◽

Pipe Surface ◽

Pipe Cross Section

The paper relates to the field of measuring technologies and deals with the enhancement of thermoconvective method when it is applied for the experimental determination of such hydrodynamics indicators as mass flow rate and velocity of flow by their indirect parameters - capacity of the heater and the temperatures obtained from two thermal sensors, provided that they are located on the hermetic piping system surface. The issue of determination of correction factor on heterogeneity of liquid temperature distribution in the pipe cross section depending on pipe diameter and fluid movement velocity was clarified. According to the results of numerical calculations, the dependencies of temperature gradient on the pipe surface and the correction factor on the heterogeneity of the temperature distribution along the pipe cross-section under the heater in the function of the velocity of flow in pipes of different diameters are plotted. These dependencies specify the thermal method of studying the fluid flow in the pipes, simplify the experiment conduction, are useful in processing of the obtained results and can be applied in measuring engineering.

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Experimental study of particle-driven secondary flow in turbulent pipe flows

Journal of Fluid Mechanics ◽

10.1017/jfm.2012.104 ◽

2012 ◽

Vol 709 ◽

pp. 1-36 ◽

Cited By ~ 12

Author(s):

R. J. Belt ◽

A. C. L. M. Daalmans ◽

L. M. Portela

Keyword(s):

Turbulent Flow ◽

Secondary Flow ◽

Stress Tensor ◽

Reynolds Stress ◽

Cross Section ◽

Circular Pipe ◽

Horizontal Pipe ◽

Pipe Cross Section ◽

Reynolds Stress Tensor ◽

Pipe Flows

AbstractIn fully developed single-phase turbulent flow in straight pipes, it is known that mean motions can occur in the plane of the pipe cross-section, when the cross-section is non-circular, or when the wall roughness is non-uniform around the circumference of a circular pipe. This phenomenon is known as secondary flow of the second kind and is associated with the anisotropy in the Reynolds stress tensor in the pipe cross-section. In this work, we show, using careful laser Doppler anemometry experiments, that secondary flow of the second kind can also be promoted by a non-uniform non-axisymmetric particle-forcing, in a fully developed turbulent flow in a smooth circular pipe. In order to isolate the particle-forcing from other phenomena, and to prevent the occurrence of mean particle-forcing in the pipe cross-section, which could promote a different type of secondary flow (secondary flow of the first kind), we consider a simplified well-defined situation: a non-uniform distribution of particles, kept at fixed positions in the ‘bottom’ part of the pipe, mimicking, in a way, the particle or droplet distribution in horizontal pipe flows. Our results show that the particles modify the turbulence through ‘direct’ effects (associated with the wake of the particles) and ‘indirect’ effects (associated with the global balance of momentum and the turbulence dynamics). The resulting anisotropy in the Reynolds stress tensor is shown to promote four secondary flow cells in the pipe cross-section. We show that the secondary flow is determined by the projection of the Reynolds stress tensor onto the pipe cross-section. In particular, we show that the direction of the secondary flow is dictated by the gradients of the normal Reynolds stresses in the pipe cross-section, $\partial {\tau }_{rr} / \partial r$ and $\partial {\tau }_{\theta \theta } / \partial \theta $. Finally, a scaling law is proposed, showing that the particle-driven secondary flow scales with the root of the mean particle-forcing in the axial direction, allowing us to estimate the magnitude of the secondary flow.

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Pipe Ovalization Prediction for the Pipe-Laying Ocean System

Volume 8: Seismic Engineering ◽

10.1115/pvp2018-84785 ◽

2018 ◽

Author(s):

Matěj Bartecký ◽

Radim Halama

Keyword(s):

Plastic Deformation ◽

Cross Section ◽

Process Simulation ◽

Model Calibration ◽

Material Model ◽

Pure Bending ◽

Pipe Cross Section ◽

Technical Practice ◽

Chaboche Model ◽

Insight Into

This contribution brings a new insight into pipe cross section ovalisation due to plastic deformation during pipe-lying process to the seabed. Firstly, the influence of material model calibration on ovalization prediction is presented on pure bending case including the Prager model, the Chaboche model and the modified Abdel-Karim–Ohno model. The mechanism responsible for cross section ovalisation was identified as the phenomenon of the accumulation of plastic deformation, the so-called ratcheting. The next part of this contribution presents main results of the pipe-laying process simulation. The pipe cross-section behavior during passing the considered pipe-laying system is studied in detail. A macro based solution makes possible to do a parametric study and to easily apply the offshore standard DNV-OS-F101 in technical practice.

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Effect of Pipe Inclination on Solids Distribution in Partially Stratified Slurry Flow

Volume 5: Multiphase Flow ◽

10.1115/ajkfluids2019-5397 ◽

2019 ◽

Author(s):

Václav Matoušek ◽

Jan Krupička ◽

Jiří Konfršt ◽

Pavel Vlasák

Keyword(s):

Uniform Distribution ◽

Cross Section ◽

Inclination Angle ◽

Concentration Profile ◽

Stratified Flow ◽

Concentration Profiles ◽

Horizontal Pipe ◽

Pipe Cross Section ◽

Test Loop ◽

Pipe Inclination

Abstract Partially stratified flows like flows of sand-water slurries exhibit non-uniform distribution of solids (expressed as a vertical profile of local volumetric concentration) in a pipe cross section. The solids distribution in such flows is sensitive to pipe inclination. The more stratified the flow is the more sensitive its concentration profile is to the pipe slope. In general, the distribution tends to become more uniform (less stratified) if the inclination angle increases from zero (horizontal pipe) to positive values (ascending pipe) up to 90 degree (vertical pipe). In a pipe inclined to negative angles (descending pipe) the development is different. The flow tends to stratify more if it changes from horizontal flow to descending flow down to the angle of about −35 degree. If the angle further decreases towards −90 degree, then the flow becomes less stratified reaching uniform distribution at the vertical position. This also means that the same flow exhibits a very different degree of stratification in ascending and descending pipes inclined to the same (mild) slope say between ±10 and ±40 degree. The rather complex development of the solids distribution with the variation of the inclination of pipe is insufficiently documented experimentally and described theoretically in predictive models for a concentration profile in partially stratified flow. In order to extend the existing limited data set with experimental data for partially stratified flow of medium sand slurry, we have carried out a laboratory experiment with the slurry of narrow graded fraction of sand with the mean grain size of 0.55 mm in our test loop with an invert U-tube inclinable to arbitrary angle between 0 and 90 degree. A pipe of the loop has an internal diameter of 100 mm. Both legs of the U-tube have a measuring section over which differential pressures are measured. Radiometric devices mounted to both measuring sections sense concentration profiles across a pipe cross section. Furthermore, the discharge of slurry is measured in the test loop. In the paper, experimental results are presented for various inclination angles with a small step between 0 and ±45 degree and a development in the shape of the concentration profiles with the changing inclination angle is analyzed. For the analysis, it is critical to distinguish between suspended load and contact load in the flow as the two loads tend to react differently to the flow inclination. The measured concentration profiles and pressure drops are compared with predictions by the layered model adapted for taking the flow inclination into account.

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Analysis of Thermal Stratification and Fatigue Stress for Pressurizer Surge Line

18th International Conference on Nuclear Engineering: Volume 5 ◽

10.1115/icone18-29366 ◽

2010 ◽

Author(s):

Xiaofei Yu ◽

Yixiong Zhang

Keyword(s):

Cross Section ◽

Thermal Stratification ◽

Thermal Stresses ◽

Structural Integrity ◽

Bending Moments ◽

One Dimensional ◽

Pipe System ◽

Pipe Cross Section ◽

Fatigue Stress ◽

Surge Line

Thermal stratification of pressurizer surge line induced by the inside fluid brings on global bending moments, local thermal stresses, unexpected displacements and support loadings of the pipe system. In order to confirm the structural integrity of pressurizer surge line affected by thermal stratification, this paper theoretically establishes thermal stratified transient and studies the calculation method of thermal stratified stress. A costly three-dimensional computation is simplified into a combined 1D/2D technique. This technique uses a pipe cross-section for computation of local thermal stresses and represents the whole surge line with one-dimensional pipe elements. The 2D pipe cross-section model is used to compute elastic thermal stresses in plane strain condition. Symmetry allows half the cross-section to be considered. The one-dimensional pipe elements model gives the global bending moments including effects of usual thermal expansion and thermal stratification of each model nodes. This combined 1D/2D technique has been developed and implemented to analyze the thermal stratification and fatigue stress of pressurize surge line in this paper, using computer codes SYSTUS and ROCOCO. According to the mechanical analysis results of stratification, the maximum stress and cumulative usage factor are obtained. The stress and fatigue intensity of the surge line tallies with the correlative criterion.

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Experimental Observations of Flow Instability in a Helical Coil (Data Bank Contribution)

Journal of Fluids Engineering ◽

10.1115/1.2910157 ◽

1993 ◽

Vol 115 (3) ◽

pp. 436-443 ◽

Cited By ~ 37

Author(s):

D. R. Webster ◽

J. A. C. Humphrey

Keyword(s):

Cross Section ◽

Flow Instability ◽

Time Integration ◽

Circular Cross Section ◽

Frequency Doubling ◽

Outer Wall ◽

Data Bank ◽

Curvature Radius ◽

Number Range ◽

Pipe Cross Section

Experimental observations were made for the nominally fully developed flow through a helically coiled pipe of circular cross-section with a curvature radius to pipe radius ratio Rc/a = 18.2. Laser-Doppler measurements of the instantaneous streamwise velocity, uθ, and the cross-stream circumferential velocity, uφ, components were obtained along the midplane of the pipe cross-section. The Reynolds number range explored was 3800 < Re < 10500 (890 < De < 2460) and spans the laminar and turbulent flow regimes. Time integration of the velocity records has yielded previously unavailable mean and rms velocity profiles. In the range 5060 < Re < 6330, the time records of the velocity components reveal periodic flow oscillations with St ≈ 0.25 in the inner half of the pipe cross-section while the flow near the outer wall remains steady. A frequency doubling (St ≈ 0.5) is also observed at some midplane locations. This low frequency unsteadiness is distinct from the shear-induced turbulent fluctuations produced with increasing Re first at the outer wall and later at the inner wall of the coiled pipe. Simple considerations suggest that the midplane jet in the recirculating cross-stream flow is the source of instability.

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Spontaneous Liquid-Liquid Slug Flow in Microchannels

Fluids Engineering ◽

10.1115/imece2006-15529 ◽

2006 ◽

Author(s):

Joseph E. Hernandez ◽

Jeffrey S. Allen

Keyword(s):

Cross Section ◽

Cross Sections ◽

Slug Flow ◽

Liquid Surface ◽

The Self ◽

Viscous Resistance ◽

Liquid Slug ◽

Interfacial Tensions ◽

Liquid Surfaces

Spontaneous liquid-liquid slug (bislug) flow in microchannels has been observed for both circular and square cross sections. Flow is induced via an imbalance in interfacial tensions and curvatures between the two gas-liquid surfaces and the liquid-liquid surface. Bislug flow in square cross-section microchannels is generally much quicker than bislug flow in circular capillaries for a variety of reasons; including the self-wetting nature of the microchannel and the decrease in viscous resistance in the corners.

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Development of a CFD-Based Coal Pipe Design Tool

ASME 2005 Power Conference ◽

10.1115/pwr2005-50130 ◽

2005 ◽

Author(s):

Gengxun Huang ◽

Kenneth M. Bryden

Keyword(s):

Power Plant ◽

Cross Section ◽

Small Region ◽

Design Tool ◽

Plant Performance ◽

Design Stage ◽

Radius Of Curvature ◽

Outlet Cross Section ◽

Curved Pipe ◽

Pipe Cross Section

In a coal-fired power plant, pulverized coal, using air as a transport medium, is pneumatically transported toward different burner nozzles by splitting the large pipe into small pipes through bifurcators or trifurcators. The combustion efficiency of the burner is dependent on matching the air and coal in these pipes. Increasingly tight emission standards also make the balance of air and coal a very critical factor for the success of the power plant. Coal roping occurs when the gas-solid flow passes through a curved pipe. The momentum of the particles carries them to the outside of the wall, concentrating in a small region. Therefore, the particle concentration in this small region is much higher than the other part of the pipe cross-section. Coal roping upstream of a coal distributor (bifurcator) can create a significant imbalance in coal loading in the split between the two branches. This can significantly impact plant performance and increase NOx production. Previous research [2] has shown that coal rope characteristics depend on many parameters; the geometry (i.e., elbow radius of curvature-to-pipe diameter ratio, pipe orientation, orifice opening, and the locations of orifices) of the coal pipe, which is determined at the design stage, will strongly affect the coal distribution in the outlet of coal pipes. This characteristic of coal roping indicates that optimizing the pipe geometry may be helpful in getting a more uniform coal distribution at the pipe’s outlet cross-section and minimizing the problems caused by imbalance between burners. In this paper, we present the CFD-based coal pipeline design tool to achieve the evenly distributed coal particle distribution across the pipe cross-section.

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