Pipe Contraction Research Articles

An exact solution of the lubrication equations for the Oldroyd-B model in a hyperbolic pipe

An exact analytical solution of the lubrication equations for the steady, isothermal, incompressible flow of a viscoelastic Oldroyd-B fluid in a hyperbolic cylindrical contracting pipe is derived. The solution is valid for values of the Deborah number, De, up to order unity (De is defined as the ratio of the longest relaxation time of the polymer to the characteristic residence time of the fluid in the pipe), all values of the ratio of the polymer viscosity to the total viscosity of the fluid, η, and typical values of the contraction ratio, Λ, encountered in experiments and practical applications. It is provided in terms of the streamfunction only and is used in the momentum balance to derive a strongly non-linear ordinary differential equation of second order with unknown a function which corresponds to a modified fluid velocity along the main flow direction. The final equation is solved semi-numerically using a fully spectral (Legendre)-Galerkin approach to resolve the unknown function almost down to machine accuracy. The exact solution for the polymer extra-stresses, which is emphasized is not the full solution of the complete lubrication equations, allows for the derivation of a variety of theoretical expressions for the average pressure-drop along the pipe. In all cases, a decrease in the pressure drop compared to the Newtonian value with increasing De, η and/or Λ is predicted. The differences between the corresponding analytical solution for the planar geometrical configuration are also identified and discussed.

Comparative investigation on high-pressure flow accelerated corrosion at gradual contraction and gradual expansion pipes

In current study, the flow accelerated corrosion behaviors of X65 steel gradual contraction and gradual expansion pipes under high-pressure conditions were comparatively investigated by establishing dynamic in situ electrochemical tests under high CO2 partial pressure conditions in a loop apparatus. The findings indicate that the corrosion rate is reduced along the flowing direction of gradual contraction pipe. Nevertheless, the corrosion rate firstly descends and subsequently ascends along the flowing direction of gradual expansion pipe, and the lowest corrosion rate is presented in inclination segment close to the straight pipe with large diameter. The corrosion rate at the top wall of gradual contraction pipe is symmetrical to that at the bottom wall, while it is asymmetrically distributed at the top wall and the bottom wall of inclination segment in gradual expansion pipe. The distribution of corrosion rate is correlated with the flow fields at gradual contraction and gradual expansion pipes. Furthermore, the special corrosion rate distribution at inclination segment of gradual expansion pipe is ascribed to the formation of secondary flow and vortexes.

Boil-off gas precooling process for subsea low temperature LNG pipelines

Moving liquefied natural gas (LNG) ports offshore and transporting LNG to the coast through submarine pipelines can address the required water depth for LNG tankers and prevent potential safety hazards at ports in crowded waterways. At ultra-low LNG temperatures (−160 °C), pipelines should be precooled by LNG boil-off gas (−120 °C) before normal operation to avoid instantaneous LNG gasification and sharp pipe contraction. In the present study, a transient mathematical model was developed for the precooling process in a subsea multilayered LNG pipeline. Heat conductivity varied with temperature, and the governing equations were solved using the finite difference method. Additionally, the effects of pipe size, insulation layer thickness, and insulation material were investigated. The precooling time decreased significantly with increasing pipe size, and a pipe diameter in the range of 30” to 40” was suitable. In terms of economy and practical applications, the thickness of the insulation layer was suggested to be 30–60 mm. Moreover, compared with glass foam insulating material, rigid polyurethane foam exhibited better thermal performance during the precooling process. These results can assist in determining a safe precooling process for subsea LNG pipelines, providing a suitable green alternative to fossil fuels.

Flow accelerated corrosion of X65 steel gradual contraction pipe in high CO2 partial pressure environments

Flow accelerated corrosion (FAC) behavior of X65 steel gradual contraction pipe in high CO2 partial pressure environments was investigated by in situ dynamic high pressure electrochemical measurements with Ag/AgCl reference electrode in FAC loop and microscopic characterization analysis. The corrosion rates in dynamic high CO2 partial pressure environments are obviously enhanced compared with those in dynamic atmospheric pressure and static high pressure environments. The FAC mechanism at gradual contraction pipe in high pressure environments exhibits significant distinction from that in atmospheric pressure environments. The variation of corrosion rates is associated with the hydrodynamics at gradual contraction pipe. The presence of high CO2 partial pressure under fluid flowing accelerates rupture of corrosion product scales.

An impact of thermal boundary conditions on characteristics of a non-Newtonian fluid flowing through a sudden pipe contraction

An impact of thermal boundary conditions on characteristics of a non-Newtonian fluid flowing through a sudden pipe contraction

Hydrodynamical instability of newtonian flow of downstream on axisymmetric sudden contraction

Measures to reduce energy losses in pipeline transport systems must be implemented already at the design stage. In particular, this also applies to local resistances of pipelines. In the paper, the separation length and separation height downstream of the contraction plane of axisymmetric sudden contraction of the circular pipe of a single-phase Newtonian flow have been investigated. Area ratios 0.250 and 0.321 were considered. After all, measures to reduce energy losses on the axisymmetric sudden contraction must be effective at values of the area ratio not less than 0.250. The separation length and separation height have the extreme dependence with a maximum at the transition of the laminar flow into a turbulent flow one. When the values of the Reynolds number at the laminar flow increase, these sizes increase, and they decrease at the turbulent flow. In the first case, the separation point is shifted downstream from the plane of contraction. The separation length and separation height are proportional to the Reynolds number. This is similar to changing the separation length and separation height of upstream from the plane of contraction. A transition zone be located between 9650 and 40000 and 1200 and 5000 if the Reynolds number is based on smaller pipe diameter and step height correspondingly. The separation length of downstream of the contraction plane are decreased if these sizes are length - smaller pipe diameter ratio, and increase if these sizes are length - step height ratio. The changing of separation height is similar. But the change of the separation length is greater than the change of separation height. There is enough good agreement between the experimental results and the results described in the literature. For taking measures providing decrease in energy losses, the investigation of the separation length and separation height downstream of the contraction plane at different values of area ratio being more than 0.250 is proposed.

Consideration of Airflow Aided Single High-Speed Droplet Generation Method

The water hammer pressure at the high-speed droplet impact has not yet been elucidated, and a reproducible droplet generator is needed to investigate it. We developed a single droplet generation device using airflow with an abrupt contraction pipe. We obtained higher velocity droplets than the smooth convergence tube of the early study. To clarify the reasons, we investigated the details of the droplet acceleration using the fluid analysis software OpenFOAM, especially focusing on the pressure gradient force in the abrupt contraction pipe. Comparing the experimental and simulation results, we found that the pressure gradient force has a small contribution to the droplet acceleration and the drag force is dominant for the motion. After examining various shapes, such as a combination of a smooth convergence with a straight pipe, we found that applying as large a drag force as possible at the beginning of acceleration leads to efficient acceleration.

HYDRODYNAMICAL INSTABILITY OF NEWTONIAN FLOW BEFORE AN AXISYMMETRIC SUDDEN CONTRACTION

The sizes of the vortex region before the axisymmetric sudden contraction of the circular pipe at the Newtonian flow have been investigated. Area ratios 0.250 and 0.500 were considered. The sizes of the vortex region have the extreme dependence with a maximum at the transition of the laminar flow into a turbulent flow one. When the Reynolds number at the laminar flow increase, these sizes also increase, and they decrease at the turbulent flow. In both cases, the sizes of the vortex region are proportional to the Reynolds number. A transition region between laminar flow and turbulent flow lies in the range of the Reynolds number from 3000 to 5300 and 750…1300, determined by the diameter of a bigger pipe of sudden expansion and a step height correspondingly

Profiling of sudden contraction of circular pipe by sharp-edged pipe insert

Measures to reduce energy losses in pipeline transport systems must be implemented already at the design stage. In particular, this also applies to local resistances of pipelines. For symmetrical sudden pipe contraction, one of such measure is profiling using insert. The paper considers a sharp-edged pipe insert, which in comparison with others has larger areas of flow separation. The diameter of the insert was calculated as the arithmetic mean between the diameters forming the sudden pipe contraction. Using the methodology described in the literature, the contraction length ratio as the areas of influence between two symmetrical sudden contractions of a circular pipe during the flow of a single-phase turbulent flow of Newtonian fluid was investigated. The coefficient of mutual influence of these local resistances was determined by formulae for direct-flowing and non-direct-flowing locking devices, which simulated symmetrical and asymmetrical fluid flow after the constriction plane, respectively. The contraction rate from 0.064 to 0.696 inclusive are considered. According to the results of calculations, no mutual influence of two sudden contractions of circular pipe was found. This indicates the unsuitability of using formulae for locking devices in this methodology for determining the contraction length ratio. Therefore, to study this problem on the sudden pipe contraction with different contraction rates, it is proposed to conduct a physical experiment. In a mathematical experiment, you can use formulae to determine the following values: upstream recirculation length and downstream recirculation length; inlet length of cylindrical pipes with turbulized the flow devices; length of the velocity profile stabilization after local resistances.

The effects of pipe length on gas cloud explosion characteristics in the contraction pipe

ABSTRACT To study the influence of pipe length on premixed gas explosion characteristics in a contraction pipe. A Large Eddy Simulation (LES) and Zimont combustion model was used to simulate the propane/air explosion process at different pipe lengths. The results show that the flame propagation velocity in the contraction pipe increases first and then decreases and reaches its peak at the change of pipe diameter. Compared with the diameter pipe, the flame propagation velocity in the first half of the contraction pipe is reduced by adding the contraction structure. Although the flame propagation velocity increases suddenly after the flame passes through the contraction pipe, the flame propagation process is effectively delayed. Compared with the diameter pipe, the total combustion time of the contraction pipe increases by 44.4%, 30%, and 30%, respectively. Under different pipe lengths, the trend of pressure change is to increase first and then decrease, and the longer the pipe, the greater the maximum explosion pressure in the pipe. The existence of the variable diameter structure leads to a significant increase of the peak pressure in the pipe, and the peak pressure in the contraction pipe is, respectively, 8, 4, and 7 times that in the diameter pipe of the same length. Therefore, in actual industrial production, it is necessary to take safety measures such as pressure relief at the change of pipe diameter to avoid accidents.

Non-Newtonian fluid flow through a sudden pipe contraction under non-isothermal conditions

• Simulation of a non-isothermal viscoplastic fluid flow through a sudden contraction. • Investigation of the flow structure with unyielded regions and rigid static zones. • Extension of two-dimensional flow zones in the contraction plane vicinity. • Effect of the governing parameters on the local resistance coefficient. A steady-state laminar flow of a viscoplastic fluid through an axisymmetric sudden pipe contraction under non-isothermal conditions has been studied numerically. Mathematical formulation of the problem is given using stream function – vorticity – temperature variables. Rheological properties of the fluid are described by the Herschel–Bulkley model, which implies an unyielded region formation in the flow. Viscous dissipation effects and temperature dependence of the viscosity are taken into account when simulating the process. An asymptotic time solution of unsteady flow equations is used to obtain a steady-state solution to the initially formulated problem. The finite-difference method based on the alternative directions scheme is applied to solve the problem numerically. Regularization of the rheological equation is performed to provide a through computation of the flow with unyielded regions. A parametric investigation of the flow structure, which includes dead zones and yielded/unyielded regions, is implemented in order to show the impact of main dimensionless parameters.

Effect of viscous dissipation on the flow structure and pressure losses for a viscoplastic fluid flow through a sudden pipe contraction

A viscoplastic fluid flow through an axisymmetric sudden pipe contraction is studied numerically in a laminar regime under non-isothermal conditions. Governing equations are written in terms of stream function – vorticity – temperature variables. A modified Schwedoff -Bingham rheological model is used to describe characteristics of the fluid. The problem is solved by the finite-difference method based on the alternative directions scheme. Simulation of the process involves taking into account viscous dissipation effects and temperature dependence of viscosity. Distributions of flow characteristics and flow structures are shown and compared with those obtained in the case when viscous dissipation is neglected. A local resistance coefficient is calculated and presented as a function of the Brinkman number.

Thermal impacts on pressure transient tests using a coupled wellbore/reservoir analytical model

This work investigates the impact of temperature effect on pressure-transient measurements made at any gauge location along a slanted wellbore completed with a production tubing. The analysis is based on a coupled transient-wellbore/reservoir thermal analytical model, which considers flow of a slightly compressible, single-phase fluid in a homogeneous infinite-acting reservoir system. The analytical model provides temperature- and pressure-transient data for drawdown and buildup tests, accounting for Joule-Thomson, adiabatic fluid-expansion, conduction and convection effects. Regarding pressure transient analysis (PTA), thermal distorted pressure data might lead to the interpretation of false geological heterogeneities, because the transient heat loss during the buildup period provides an increase in the pressure exerted by the wellbore-fluid column and a change in the gauge location due to pipe contraction. Though some of the derived expressions are lengthy, they encompass an intrinsic simplicity in that one can compute pressure- and temperature-transient data on a spreadsheet. Analytical results are compared with those of a commercial thermal wellbore/reservoir simulator showing a good agreement. Thermal impacts on PTA interpretations are demonstrated by showing that a homogenous reservoir can be wrongly interpreted as a double-porosity system. A field case is presented, consisting of a drill stem test conducted in a multi-layered heterogeneous reservoir.

In situ study of flow accelerated corrosion and its mitigation at different locations of a gradual contraction of N80 steel

A gradual pipe contraction may cause severe localized corrosion resulted from the flow acceleration, thus threating the operating safety of pipelines in the oil and gas field. Until now, the quantitative study on the correlation between local corrosion rate and local hydrodynamics at the gradual pipe contraction is still missing.In this work, the flow accelerated corrosion and its mitigation at different locations of a gradual pipe contraction of N80 steel are in situ investigated using computational fluid dynamics simulation and array electrode technique combined with electrochemical impedance spectroscopy. The results show that the distribution of corrosion rate at the gradual pipe contraction is in good accordance with the distribution of hydrodynamics parameters including flow velocity and wall shear stress, i.e., the higher flow velocity or higher wall shear stress is, the higher local corrosion rate is. The presence of an imidazoline derivative inhibitor can greatly mitigate the corrosion at the gradual pipe contraction through hindering the mass transfer process and charge transfer process of corrosion. Furthermore, in the presence of inhibitor the differences in corrosion rate among different locations at the gradual pipe contraction are also effectively reduced, or even disappeared at low flow velocity. Therefore, the addition of the inhibitor is an effective way to mitigate or even eliminate the flow accelerated corrosion at the gradual pipe contraction in the oil and gas field.

Analysis of energy losses in smooth pipes

Pipe is a closed conduit, usually of circular section, which is used for carrying fluids under pressure. The pipe running partially full, in such a case atmospheric pressure exists inside the pipe, also behaves like an open channel. In general, energy or head losses on pipe consisted of major energy losses due to friction and minor energy losses due to sudden enlargement of pipe, sudden contraction of pipe, bend in pipe, an obstruction in pipe, pipe fittings etc. The main purpose from this research is to analyse energy losses in smooth pipes. There are several steps in analysing such as calculating Reynolds Number (Re) in order to determine flow type, calculating friction factor by using several formulas, and calculating roughness value (k) on smooth pipe with different various scenarios. The experimental study was performed at Hydraulics and Fluid Mechanics Laboratory to process the analysis. The results indicated that the flow type is turbulent when Reynolds Number (Re) is more than 4000. The turbulent flow is characterized by random and irregular movement of fluid particles. The other result also shown that roughness value (k) in smooth pipe is inverse proportion to Reynolds Number.

Study of gas-liquid upward annular flow through a contraction

Transient response of two-phase flow is important in many analyses of nuclear reactor accident scenarios. In the present work, we study the response of vertical annular flow to a sudden or gradual pipe contraction. The three component fields of gas-liquid annular flow, namely, the liquid film, the entrained liquid droplets and the gas core, show different behaviour as they pass through an area change section because of their very different inertias. Pressure variation through the contraction is a result of the integrated effect of these responses. In order to throw light on these, pressure profiles along the upstream and downstream sections of the contraction have been measured in air-water flow through a vertical converging pipe section for diameter ratios of 1.5 and 2.0 and for half-cone angles of 8°, 15° and 90°. The gas-droplet field interaction has been studied using computational fluid dynamics simulations while the gas-film flow interaction has been studied using an analytical model for film flow. These studies highlight the role of droplet inertia as the principal contributor to the pressure change in the contraction. A semi-empirical model has been developed for the pressure loss coefficient in the contraction.

Testing of smoothed particle hydrodynamics method for minor loss coefficient in three-dimensional water flow in circular vertical pipe contraction

Smoothed Particle Hydrodynamics method has been developed rapidly as an alternative numerical method to solve the fluid physics problem. This meshless method is able to identify the physical entity of each fluid by interpolating the corresponding physical entity associated with the neighboring particles within the influence domain. Three-dimensional fluid flows on circular vertical pipe contraction were studied by using this method. The numerical model will be simulated by varying the number of fluid particles and the number of kernel particles within the influence domain. The conservation of mass, conservation of energy and the minor loss coefficient will be evaluated. The mass conservation and energy conservation will be reached by considering the appropriate number of initial particles and kernel particles. The results of the minor loss coefficient achieved from the numerical simulation are between 1.992 and 2.836.

Fluid characteristic of liquid nitrogen flowing in HTS cable

For long distance operation of High-temperature superconducting (HTS) cables, evaluations of heat transfer and fluid flow dynamics of liquid nitrogen (LN2) flowing in the HTS cable is important. However, the LN2 flow is complicated when the cable core is housed in a spiral corrugate cryostat-pipe and positioned at an eccentric position to the center of the cryostat-pipe. In this study, the effect of a configuration of a spiral corrugate cryostat-pipe on the pressure drop was evaluated using computer simulation. As a result, it was confirmed that the calculated pressure drop in the spiral corrugate pipe is 17 times larger than that in the straight pipe due to the shrinking and expanding of the LN2 flow at the concave domain. This shrinking and expanding of LN2 flow was assumed to be the flow in a gradual contraction pipe and a gradual expansion pipe respectively, so that the pressure drop was calculated by a theoretical arithmetic analysis. For verification of this calculation, the calculated value was compared with the measured value of a HTS cable system, which was constructed in NEDO project. As a result, these values were agreed well each other and it indicated that the pressure drop in the spiral corrugate pipe could be evaluated by this calculation.

Study on Hydraulic Flow in Stratified Pipe Performed by Numerical Simulation

An idea of introducing an underground floodway inspired by Storm-water Management and Road Tunnel (SMART) in Malaysia is considered attractive to minimize land utilization regarding to the flood problem in Jakarta. This research was aimed to know the flow behavior of this modified tunnel due to sudden transitions, pressure losses and loss coefficients using numerical modeling. The simulation was conducted in the three-dimensional model using FLUENT Software which was divided into three models, i.e., contraction, enlargement, and straight pipe model. The simulation model was followed the geometrical design of SMART which the area ratio between smaller and larger pipe, A1/A2 varied, namely 0.20, 0.50, and 0.80. Standard k-ε and equilibrium wall function were used in straight pipe model, while contraction and enlargement model used k-ε modified and non-equilibrium wall function. The effect of different Reynolds number was also studied in this research. The result of the simulation showed that hydraulic parameters and area ratio of sudden transitions pipe give significant effect towards losses along the pipe. FLUENT simulation result gave good agreement with Darcy-Weisbach formula. The results indicate that loss coefficient decreases with the increase in pipe area ratio. The increase in pressure head loss was incurred by severe separated regions in the vicinity of pipe transition which was proved by typical flow pattern. Variation of Reynolds number also showed a different area of separation flow, yet the flow pattern was somewhat similar.

Study on the Physical Characteristics of Water Supply Steel Pipe according to Temperature Change

‘The facilities standards of water supply’ issued by the Ministry of Environment in 2004 indicates that expansion joints cannot be used in welding water supply steel pipes. However, their reason is not clear and it is difficult to confirm the stability of the steel pipe for a water supply pipeline. The purpose of this study is to determine whether or not an expansion joint is necessary to improve the stability of water supply in steel pipe through a displacement analysis of the pipework. The test results are as follows. Firstly, it was found that expansion and contraction of the water supply steel pipe (D2,400 mm) occur repeatedly in 4 cycles per year, and the maximum expansion and contraction amount of the pipe is 13.03 mm in 1.24 km pipelines. Secondly, the thermal stress caused by expansion and contraction of the steel pipe is 13.7~36.1kgf/cm2 according to the burial depth (0~4 m). The main comparison factors to determine the stability of the steel pipe (STWW 400) were the allowable tensile strength and the fatigue limit, which were computed to be 4,100 kgf/cm2 and 1,840 kgf/cm2, respectively. Finally, the thermal stress of the steel pipe is very small compared to the allowable tensile stress and fatigue stress. Therefore, thermal stress does not affect the stability of the steel pipe, although the expansion and contraction of the steel pipe occurs by temperature changes. In conclusion, the study demonstrated that expansion joints are not required in water supply steel pipelines. Key words: Thermal Stress, Expansion Joint, Expansion Chamber, Stability of the Water Supply Steel Pipe