412 research outputs found
Experiments in stratified gas-liquid pipe flow
No full textThe growing demand for energy in the future will necessitate the production of natural gas from fields which are located farther offshore, in deep water and in very cold environments. This will confront us with difficulties in ensuring continuous production of the fluids (natural gas, condensate and water) emerging from a natural gas well. Often, all the three phases are transported together through a multiphase flow pipeline to processing facilities onshore. The natural gas production pipelines that carry the wellstream fluids from the subsea wells to the processing facilities are designed using engineering multiphase flow models. It is known that the currently available flow models cannot predict the most important flow parameters such as pressure drop and liquid holdup with sufficient accuracy when the gas production is low. At these conditions, the liquid accumulates in V-sections (lower elbows, low spots) of a pipeline, which are present because the pipeline profile follows the undulations in the seafloor topography. When the flow is low, the existing engineering models show large uncertainty in predicting the shear stresses, particularly at the gas-liquid interface. This uncertainty leads to the inaccurate prediction of, for example, the liquid holdup, which can cause production problems connected with liquid slugs, corrosion and the formation of gas hydrates. In this Thesis, the problem of liquid accumulation in an undulating pipeline is studied both at a more general, macroscopic level in a flowloop that contains a V-shaped section, as well as on a detailed, fundamental level in a straight horizontal pipe. Both configurations, however, have the same flow pattern: stratified gas-liquid flow. The main issues addressed in the V-section setup are the conditions of liquid accumulation and removal in the case of zero net liquid flow with gas flowing over a stagnant liquid pool, as well as the appearance of multiple steady-state solutions in the two-phase models at these conditions. The detailed measurements in the horizontal setup aimed at simultaneously capturing the velocities in both phases in the entire streamwise cross-section of the pipe and the position of the gas-liquid interface. This provided detailed information on waves and turbulence, which are the main phenomena in stratified flow. The occurrence of multiple solutions in stratified flow models was studied by applying a steady state and a transient model to various conditions for which lab experiments exist and by verifying the structural stability of the obtained solutions. It was found that the applied transient model (supplied with the criterion for structural stability) can qualitatively predict the measurements in zero net liquid flow, at conditions where hysteresis occurs and in experiments with a holdup discontinuity. Based on the comparison with available experimental data, it was concluded that hysteresis can only occur in fully laminar flow of both phases, and it is not expected to occur at typical field conditions. However, to achieve a better quantitative agreement with the measurements, the closure relations used in the model need to be improved. Measurements of the gas velocity, liquid holdup and pressure drop in zero net liquid flow were performed in a setup containing a V-shaped section. It was shown that the critical gas velocity (i.e. the minimum gas velocity at which the liquid is removed from the low spot) and pressure gradient increase with increasing inclination angle and with increasing liquid density and viscosity, while the liquid holdup stays approximately the same. The results were compared to the predictions of a mechanistic flow model, which was modified to account for the recirculation in the stagnant liquid layer at critical conditions by employing a theoretical solution for the wall shear stress at laminar flow conditions of the liquid. Good agreement was found between the measurements and the simulations. Stratified two-phase flow of air and water was measured with Particle Image Velocimetry (PIV) in a horizontal transparent pipe, with a laminar, transitional or turbulent liquid, and a smooth or a wavy interface. An advanced experiment was designed and built, which uses two lasers and three cameras to simultaneously measure the liquid velocity, interface shape and gas velocity. The data were time- and phase-averaged to obtain detailed and accurate insight into the turbulent and wavy structures. The cases with a smooth interface were shown to approximately follow the velocity laws valid in single-phase flows. The wavy region of the flowmap (constructed with superficial gas and liquid velocities at the axes) had waves which are asymmetric, with gravitational and capillary forces of similar magnitude. The linear wave theory provided a good approximation of the wave-induced velocity profiles, although the wave non-linearity caused a deviation close to the interface. The separation of wavy and turbulent motion was, however, only partly successful due to the wide range of wavelengths and wave heights in all the wavy cases. The laminar-to-turbulent transition of the liquid phase in stratified gas-liquid flow was also studied. The boundaries of transition were determined in both the smooth and the wavy region of the flowmap. In both regions, the Reynolds number at the start and at the end of transition decreased with increasing gas flowrate. The two occurring wave patterns (labelled `2D small amplitude' and `3D small amplitude' waves) corresponded to the capillary-gravity and the gravity-capillary solutions of linear wave theory. This led us to recast the flowmap of the wavy region into Weber number - Froude number coordinates, which in turn provided a physical interpretation of the interaction between the developing turbulence and the changing wave patterns. Finally, the interfacial characteristics and the velocities were investigated in both phases of stratified flow in two wave patterns: `3D small amplitude' and `2D large amplitude' waves. The 2D LA waves (corresponding to gravity waves) had higher and longer waves, that changed the liquid velocities in almost the entire liquid layer. The 3D SA wave pattern (corresponding to gravity-capillary waves) had smaller and shorter waves whose influence was limited to only a part of the liquid height. The effect of the two wave regimes on gas phase velocities, however, was rather similar. In all cases, waves produced an increase in the Reynolds stresses in the air close to the interface, which was linked to the occurrence of boundary layer separation at the interface. The occurrence of separation correlated well with the wave properties. The results of the current study provide a step forward in understanding stratified gas-liquid flow through straight pipes. The physical explanations and insights of the measured phenomena can be used to develop new correlations for the engineering flow models, which is the type of models that are currently widely applied in the industry. Furthermore, a high-quality experimental database for an elementary two-phase pipe flow configuration has now been established. This database can be used for the improvement and validation of more advanced models for such two-phase flows. In particular, these are Computational Fluid Dynamics (CFD) models of increasing complexity, such as Reynolds-Averaged Navier Stokes (RANS), Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS).Process and Energy, Fluid MechanicsMechanical, Maritime and Materials Engineerin
The Effect of Surfactants on Gas-Liquid Pipe Flows
No full textLiquid loading is a major problem in the natural gas industry, in which gas production is limited by the accumulation of liquids in the well tubing. Liquid loading can be prevented by the injection of surfactants at the bottom of the well. The surfactants cause the liquid in the well to foam, thereby changing the gas-liquid flow in the well. The flow is characterized by the TPC (Tubing Performance Curve), which relates the average pressure gradient in the tubing to the gas flow rate. This work has two main goals: (i) To improve the understanding of the effect of surfactants on gas-liquid flow in pipes, which we characterize by a change in the generalised TPC. The generalised TPC relates the average pressure gradient to the gas and liquid flow rates in the pipe. (ii) To provide subsidies for the development of simple physically-based models for the effect of surfactants on gas-liquid flow. We performed experiments in intermediate-scale pipes (lengths of 12 m to 18 m and diameters of 34 mm, 50 mm, and 80 mm) with air and water at atmospheric conditions, without and with surfactants. Multiple parameters, that also vary between different gas wells in the field, were varied: the gas and liquid flow rates, the pipe diameter, the pipe inclination, the surfactant type and the surfactant concentration. We performed a visualisation of the flow without and with surfactants to obtain qualitative results on the effect of surfactants on the flow morphology, and we related these results to quantitative measurements of the generalised TPC and the liquid holdup. The behaviour of the generalised TPC is to a large extent determined by the transition between annular flow and churn flow. In annular flow without surfactants, at large gas flow rates, the water is present in a film along the pipe wall and in entrained droplets in the gas core; the water always moves upwards, which leads to a relatively regular flow morphology. In the churn flow regime, which occurs at low gas flow rates, the liquid film reverses, as the interfacial friction between the gas and the liquid, which drags the liquid upwards, no longer exceeds the gravitational force on the film. This leads to a complex flow morphology, a large liquid holdup and a large pressure gradient. Surfactants cause the formation of foam through the hydrodynamics of the flow. The foam decreases the density and increases the volume of the film at the wall. This changes the balance between the interfacial friction and the gravitational force, which shifts the transition between churn flow and annular flow to lower gas flow rates. As a result, the generalised TPC is changed by the surfactants, leading to a decrease in the pressure gradient at low gas flow rates. An optimum surfactant concentration exists that results in the largest reduction of the pressure gradient. This concentration increases with increasing film thickness; therefore, it increases with decreasing gas flow rate, increasing liquid flow rate, increasing pipe diameter, and decreasing inclination from horizontal. Qualitatively, these results are unaffected by the type of surfactant that is used. From the results obtained in this work, we qualitatively understand the effect of surfactants on the gas-liquid flow, and we understand why surfactants are able to deliquify gas wells. However, a physically-based model is required to translate the results obtained in this work in a quantitative way to the large-scale gas wells. Such a model requires a characterization of the foaming behaviour of the surfactant-liquid mixture using a small-scale setup. We determined that a small-scale sparging setup, often used in the gas industry, is not suitable, because the hydrodynamics in the sparging setup differ too much from the hydrodynamics of annular flow and churn flow. A small-scale shaking test, in which the hydrodynamics more closely resemble churn flow, shows more potential to characterize the foaming behaviour of the surfactants in the context of gas-liquid flows.Chemical EngineeringApplied Science
‘Amsterdam Castle’: een Amsterdams kasteel in Muiden
No full textSinds 2011 wordt het Muiderslot in de markt gezet als ‘Amsterdam Castle’. Aan het middeleeuwse Muiderslot is de afgelopen eeuwen flink gesleuteld. Ook de wijze waarop het Muiderslot sinds de eerste, negentiende-eeuwse restauratie gepresenteerd wordt aan het publiek is aan voortdurende verandering onderhevig. Sophie van Doornmalen, Tessa Henkes, Benthe van Houtum, Anne Kamphorst, Jacob Knegtel, Hanneke Ronnes, Steff van Seijen en Misty Zonneveld beschrijven de recente transformatie tot ‘Amsterdam Castle’ en de betekenis daarvan voor het historisch erfgoed
By-pass pigging: Experiments and simulations
No full textPipelines are used in many industries as a means of transporting fluids, for example in the oil and gas industry. Pigs are devices that move through such pipelines, for instaoce to cleao the pipeline or to perform internal inspections. They are driven by a pressure difference over the pigs. Since this is a risky operation, there is a strong motivation to control the motion of these pigs. One possibility is to use so-called by-pass pigs. These pigs have a hole through their body such that fluids cao by-pass the device. This lowers the pig velocity. If the by-pass area cao be varied during a pigging operation, it is possible to control the pig velocity. This concept is relatively new aod not yet completely understood. Research is currently carried out at the TU Delft in collaboration with Shell to get abetter understaoding of the behaviour of conventional pigs of by-pass pigs. This MSc thesis is part of that project aod focuses on performing experiroents for pigging operations in a laboratory environment. The relevance is two-fold From one haod, more insight will be obtained in the encountered phenomena From the other hand, the results can be used to validate the numerical pigging model which is currently in development. The experiroents were carried out in a flowloop at the department of Process & Energy at the TU Delft. The flowloop has a length of 65 m aod a diameter of about 52 mm. Air is used as working fluid aod the flowloop has an atroospheric outlet pressure. Duriog the pigging experiroents, the bulk velocity aod pressure in the flowloop were recorded. Three cameras were used for visual observation from which the velocity was deduced. The modular pig design made it possible to quickly chaoge between different pig configurations. It turned out that small variations in this configuration can have large influence on the pig motion. A pre dominant characteristic of the pig motion is the so-called stick-slip motion. This motion is characterized by a quick acceleration and deceleration of the pig as a consequence of a varying friction. A module was added to the numerical pigging model to include the effect of variations in the friction, which forces the siroula tion to give a stick-slip behaviour. Besides this, also an aoalytical approach was taken to obtain first insights into this behaviour. The experiroental results show that the maximum pig velocity cao become significantly larger thao the average pig velocity. The ratio of the maximum velocity over the average velocity increases at lower bulk velocities. The stick-slip models cao give a reasonable good estimation of the maximum pig velocity. Besides this, they predict a similar trend in the pressure fluctuations. To compare the influence of the bulk velocity aod the by-pass area, ao extensive parameter study was carried out. Results of 132 pigging runs with two different types of sealing were included. The by-pass area was varied from O % to 4 % and the bulk velocity was varied in the raoge of 1.5 ml s to 7 ml s . The focus was on the effects of these chaoges on the average pig velocity, the average friction and the staodard deviation of the pressure. It turned out that the friction of the pigs used in the experiroents was not depending on the velocity. The staodard deviation of the pressure, which is a measure of the intensity of the stick-slip behaviour, was different for both types of sealing. However, for a certain configuration no dependence on the pig velocity was found. The average pig velocityitselfis largely dependent on the by-pass area. The results were compared with the numerical pigging model, a commercial package and a steady-state analytical model. Itturned out that the average velocity cao accurately be determined with all these models, even if the pig motion shows a strong stick-slip behaviour.Mechanical, Maritime and Materials EngineeringProcess and EnergyFaculty: Aerospace Engineering, Department: Aerodynamics, Wind Energy & Propulsio
Turbulence Modelling of Two Phase Stratified Channel and Pipe Flows
No full textStratified two phase flow is one of the flow regimes that is of importance in multiphase flow transport through pipelines, such as used for example in the oil and gas industry. Its application also extends to chemical production, energy conversion and food processing. The phenomenon of turbulence further complicates the stratified flow behaviour. Having a simulation tool that accurately predicts the pressure gradient and liquid level in a turbulent channel or pipe flow can lead to better designs of multiphase flow systems. The common RANS turbulence models (such as − and −) artificially produce too much turbulence at the liquid-gas interface. Therefore, these models need to be modified such that turbulent viscosity is sufficiently damped at the interface. To ensure this, in the present study the specific dissipation rate () is imposed at the interface. Here is an appropriate function of the surface roughness factor (), which represents the effect of interface waves. The present work is a follow up to a previous research project where a MATLAB tool was developed for the prediction of stratified flow in channels. The first and main objective of the present thesis is to find and test a model for and to apply that to obtain a modified version of the Standard − (SKW) turbulence model and the Shear Stress Transport (SST) model. MATLAB can be used to find solutions for the channel flow. The simulation results are compared with experimental data. The second objective is to compare the results obtained using the turbulence models in the MATLAB model with predictions using similar models in Fluent. The third objective is to extend this study to a 3D setup of a two phase pipe flow where only the liquid phase is simulated. This is a so-called Segregated Liquid Phase (SLP) simulation. RANS predictions in Fluent are compared with experiments and DNS data. The main conclusions are: . The calculation of has been automated. . The predictions of the flow rates for the experimental case by Fabre et al. are better than those for the experimental case by Akai et al. . MATLAB predictions of the flow rates for the experimental cases are better than those of Fluent. This is because it is difficult to correctly impose an interface condition in Fluent, whereas this is straightforward in MATLAB.Mechanical, Maritime and Materials EngineeringProcess and EnergySustainable Process Energy TechnologyP&E Report Number: 275
Benchmarking of Computational Fluid Dynamics for multiphase flows in pipelines
No full textApplied SciencesKramers Laboratorium voor Fysische Technologi
Measurements of gravity and gravity-capillary waves in horizontal gas-liquid pipe flow using PIV in both phases
No full textAn experimental study was performed in stratified wavy flow of air and water through a horizontal pipe. The velocity fields in both phases were measured simultaneously using PIV and the interfacial shape was resolved using a profile capturing technique. The objective of the study was to investigate the interfacial characteristics and the velocities of the liquid and gas phases in two wave patterns: ‘3D small amplitude’ and ‘2D large amplitude’ waves. The wave patterns were shown to consist of gravity and gravity-capillary waves, respectively, with substantial differences in the wave characteristics and liquid velocities. Contrary to this, the effect of the waves on the gas velocities was rather similar in both wave regimes, with both wave regimes causing an increase in the velocity fluctuations close to the interface. The current measurements also produced a valuable dataset that can be used to further improve the numerical modeling of the stratified flow pattern.Accepted Author ManuscriptFluid Mechanic
Overview of turbulence models for external aerodynamics
No full textAn overview is given on the background of different turbulence models that can be used to compute boundary layers in external aerodynamics, such as for aircraft. The overview includes algebraic models (Cebeci-Smith, Baldwin-Lomax), a half-equation model (Johnson-King), two-equation models ( K-E-K-), and a differential Reynolds-stress model. The models were compared for boundary layer without and with streamwise pressure gradient. The models were also used to study the large-Reynolds number scalings (wall function and defect layer). The comparisson of models and the sealing analysis are described in three seperate journal contributions.Aerospace Engineerin
Computation of the separation of steady and unsteady, incompressible, laminar boundary layers
No full textAerospace Engineerin
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