Severe slugging, which could induce large-amplitude pressure and flow rate fluctuations, is a major and expensive problem in multiphase transportation systems of offshore oil production system. To avoid such problem i...
Severe slugging, which could induce large-amplitude pressure and flow rate fluctuations, is a major and expensive problem in multiphase transportation systems of offshore oil production system. To avoid such problem is a basic requirement for flow assurance management. This study is an experimental and numerical investigation of severe slugging in a relatively long pipeline-riser system. A series of experiments on two-phase, air-water flow in a flexible Sshaped riser were carried out. The experimental system has a 114m long horizontal pipeline connected to a 19m long pipe which is inclined to −2degree from horizontal, followed by a 15.3m high riser operating at atmospheric end pressure. Four types of flow patterns were found and characterized by the pressure fluctuations at the bottom of the riser. A flow patter map for the prediction of severe slugging was developed based on the experimental results. The detailed characteristics of severe slugging such as pressure fluctuations, liquid holdup, under different gas-liquid superficial velocities were provided. A transient model to predict the flow behavior in the pipeline-S-shaped riser system was developed based on an existing model (OLGA). The modified model, which was tested against new experimental results obtained in this study, showed that the four types of flow patterns observed in the experiment were predicted with acceptable discrepancies. The flow pattern map was obtained using present model, as well as the detailed characteristics of severe slugging. In addition, the reasons for the difference between experimental and numerical results were analysed in this article. The motive of the numerical studies was to identify the areas that could not be reproduced by the present model and to give some suggestions for future models.
An Eulerian-Lagrangian numerical simulation is performed to study aeolian sand transport in a wind tunnel. The evolutions of three parameters, sand mass flux, decay rate of sand mass flux profile and sand particle mea...
An Eulerian-Lagrangian numerical simulation is performed to study aeolian sand transport in a wind tunnel. The evolutions of three parameters, sand mass flux, decay rate of sand mass flux profile and sand particle mean horizontal velocity with time, are investigated. The results show that: Sand mass flux takes more time to reach the saturated state than the last two parameters. First, we prove the evolution with time in the simulation is similar to the evolution in the length direction in a wind tunnel and then the experimental data from unsaturated wind tunnel can be used in the quantitative comparison with simulated saturated results. Second, detailed comparison is carried out. The tendency of sand mass flux is consistent with the experimental data. Decay rate of sand mass flux profile and sand particle mean horizontal velocity fit the experimental data well especially for cases of small free stream wind velocity, and the deviation is getting larger with the increasing of free stream wind velocity.
An improved meshless numerical method (MPS-MAFL) is utilized to simulate single Taylor bubble rising in liquid LBE to study its hydrodynamic characteristics. The computational region is a circular tube in which the li...
An improved meshless numerical method (MPS-MAFL) is utilized to simulate single Taylor bubble rising in liquid LBE to study its hydrodynamic characteristics. The computational region is a circular tube in which the liquid is described using discretized particles by un-uniform grid scheme. The gas-liquid interface was approximately treated as a free surface boundary and nonslip conditions are applied on tube wall. Several simulation results and corresponding analysis including Taylor bubble propagation procedure, pressure distribution, velocity profile around bubble nose and in the wake region as well as in the falling film are presented. Some experimental results and CFD numerical simulations from other previous researchers are compared with the present study as validation. The simulation results agree well with both theoretical analysis and experimental results, which demonstrate the reasonable selection of model as well as the accuracy and reliability of moving particle method.
Cerebral aneurysm, a local enlargement of an artery caused by weakness in the wall of a cerebral artery, has the high death rate and disability rate, and is a threat to public health. The forming mechanism of aneurysm...
Cerebral aneurysm, a local enlargement of an artery caused by weakness in the wall of a cerebral artery, has the high death rate and disability rate, and is a threat to public health. The forming mechanism of aneurysm is complex, which motivated many researchers to conduct studies in this field. The results indicated that increasing heart frequency can aggravate the oscillation of wall shear stress, and push The growth points of aneurysm along the aneurysm wall, thereby significantly affecting bthe growth and rupture mechanism of aneurysm. In addition, it is found that the curvature of the vessel is the key to induce the secondary vortex in the aneurysm; the secondary vortex increases the magnitude of WSS near the dome of aneurysm, which can cause the rupture of aneurysm dome. there is a linear relationship between the velocity of blood flow and the square root of hear frequency.
The objective of the present work is to investigate the air-water two-phase flow patterns in pipeline-riser system with an S-shaped flexible riser. The test loop with 50 mm ID consists of a horizontal pipeline with 11...
The objective of the present work is to investigate the air-water two-phase flow patterns in pipeline-riser system with an S-shaped flexible riser. The test loop with 50 mm ID consists of a horizontal pipeline with 114 m in length, a downward inclined section with 16 m in length, and an S-shaped flexible riser with 24 m in height when downward section inclined at −2° with respective to the horizontal. The inclination angle of the downward section varied from −2° to −5°. The liquid superficial velocity ranged from 0.03 to 1.5 m/s, and the gas superficial velocity from 0.4 to 6.0 m/s. Identification and characterization of flow regimes were attained by pressure at riser-base and liquid holdup at riser top. Severe slugging I, severe slugging II, transition flow and stable flows are observed to exist. flow pattern maps for each declination are presented and the transition criteria are proposed. It's found that as higher liquid and gas velocity is required for the transition of the flow in the pipeline from stratified to intermittent with increasing the declination angle, severe slugging was observed to occur over a wilder range of flow conditions. The effect of riser geometry and separator pressure on the occurrence of the flow patterns was also examined. It shows that the S-bend tends to suppress the initiation of severe slugging.
Through constructing micro-scale model, the kinetic of micelles in surfactant solution and the corresponding rheological properties are studied numerically by Brownian dynamics simulation. Rigid osculating multibead r...
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Through constructing micro-scale model, the kinetic of micelles in surfactant solution and the corresponding rheological properties are studied numerically by Brownian dynamics simulation. Rigid osculating multibead rods which can be connected at the endcaps are used to represent micelles. By analysis of potential and frictional effect, the force and kinetic of micelles in shear flow field are studied. The simulated results indicate that flexible micelles elongate along the cylindrical axis with addition of bending potential. As the persistence length increases, the characteristic zero-shear viscosity increases.
This article proceeds a new method which can continuously prepare emulsion by using a venturi tube, to achieve the goal of emulsify diesel oil, methane and water. The diesel oil comes in at the entrance of the venturi...
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This article proceeds a new method which can continuously prepare emulsion by using a venturi tube, to achieve the goal of emulsify diesel oil, methane and water. The diesel oil comes in at the entrance of the venturi tube. The solution of methane and water comes in at the throat of venturi tube and mixes with diesel oil to form emulsion. The preparation system is designed and the structure parameter of the venturi tube is calculated. Then FLUENT is used to do a series of numerical simulation of the flow in the venturi tube under different parameters of spread angle and ratio of length to diameter, thus deciding the best parameters which are 8 degree and 1.25. The basic data for the design of experimental system is provided.
Electrospinning has been proved to be a versatile and effective method for manufacturing micro-scale to nano-scale fibers continuously. In this article, CdS/ZnO core/shell nanofibers were prepared successfully by the ...
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ISBN:
(纸本)9781118205976
Electrospinning has been proved to be a versatile and effective method for manufacturing micro-scale to nano-scale fibers continuously. In this article, CdS/ZnO core/shell nanofibers were prepared successfully by the typical single-nozzle electrospinning, with subsequent simple thermal decomposition. The SEM and TEM results indicated that core-shell fibers with a diameter of 200-350 nm and shell thickness of 50nm were obtained when PVP/zinc acetate/cadmium acetate/thiocarbamide composite nanofibers were calcined at 480°C for 4h. The EDS analysis results showed that the core fiber is CdS and the shell layer is ZnO. Hydrogen evolution measurements from photocatalytic water splitting using the ZnO/CdS core-shell nanofibers as photocatalyst were carried out. The ZnO/CdS core-shell nanofibers demonstrate a much higher ability for H 2 evolution than that of sole CdS or ZnO. The highest H2 evolution rate was up to 354 μmolh-1 g-1.
Turbulent drag reducing characteristics of CTAC/NaSal aqueous solution (CTAC had same mass concentration with NaSal.) were investigated in a two-dimensional channel of 30 mm height and 375 mm width, which was made of ...
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Turbulent drag reducing characteristics of CTAC/NaSal aqueous solution (CTAC had same mass concentration with NaSal.) were investigated in a two-dimensional channel of 30 mm height and 375 mm width, which was made of transparent acrylic resin. The measured drag reduction data were scaled up by using Hoyt's scaling method and were compared with other reported drag reduction data for different channel sizes. It could be concluded that both the critical temperature and critical Reynolds number at which turbulent drag reduction of surfactant solution occurred increased with concentration. There was a maximum drag-reduction about 60% for the measured CTAC/NaSal solutions. The Hoyt's scale-up method correlated well the experimental data for different channel heights when the SIS (shearing induced structure) was established very well in surfactant solutions.
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