Transient analysis of a gas manifold system

In the present work, a numerical study has been carried out to predict transient gas flow and pressure behaviour in a gas manifold system. The start‐up and shutdown of the system, varying demands at the consumer ends, malfunctioning of compressors and valves are a few examples of common causes of transience in a gas delivery system. In particular, the sensitivity of oscillations in pressure and mass flux to variation in pipe dimensions, supply pressure and gas flow rate are ascertained under the aforementioned conditions of transience. The present results show that large pipe dimensions, high gas flow rate and high upstream pressure in the branch in which the disturbance is introduced, all cause greater amplitude in mass flux and pressure oscillations in the neighboring branches. The duration of oscillations is also found to be longer. The present study has practical importance in designing as well as in operating, a gas delivery system.     

煤层气集输管道设计影响因素研究

煤层气田的特点是煤层气组分较纯,气田单井产量低,井网分布密集且井口数量众多,井口压力较低。由于煤层气田集输管网压力较低,需建设大量管道,投资费用高。研究煤层气集输管道计算影响因素及其规律对管道参数设计和优化、降低管道总体投资具有重要意义。采用多相流模拟软件OLGA建立了煤层气集输管道水力计算模型,模拟分析了管道流量、管径、含水率、进站压力对管道压降参数的影响,得出管径是集输设计的主要影响参数。敏感性分析结果显示煤层气集输管道设计参数的关键影响因素为管径和流量,且管径的影响最大。研究对于煤层气田的集输管道的计算和设计具有指导意义。     

Modeling Nonsteady‐State Regimes of Dilute Pneumatic Conveying

The nonsteady‐state gas‐particle flows in pipelines are considered. Chaotically moving particles are described as granular gas characterized by granular temperature. This temperature dissipates because of partially inelastic particle collisions with the wall, with each other and also because of the particle viscous friction with gas. The energy losses on a microscale are translated into the pressure losses on a macroscale. The model developed is validated for both steady‐state and nonsteady‐state regimes by comparing calculated pressure losses with experimental data. A detailed numerical study of the nonsteady‐state flows shows that the pipe wall roughness is a major parameter affecting the pressure drop. Flow regimes for different particle elastic properties, particle sizes, and solids loading are studied.     

An experimental study on the choked flow characteristics of CO2 pipelines in various phases

High pressure pipeline transportation has been an established technology for economically transporting large amounts of CO_2. However, there are still issues and associated risks that have to be effectively addressed and adequately understood. It is well known that a strong Joule-Thomson Cooling effect can occur when pressurized CO_2 flows through a choke valve. Thus, to investigate the choking characteristics especially the temperature drop of high pressure CO_2, a new laboratory scale experimental setup(total length of 14.85 m and the inner diameter of 15 mm) was constructed. Steady choked flow and transient choked flow tests were carried out respectively for pressurized CO_2 in various initial phases. The phase transitions and temperature drop characteristics were then studied following the choked flow and the results show that the phase transitions in steady choked flow differs significantly from that in transient choked flow. For transient choked flow of various initial phases, all the flows downstream would transfer from single phase to gas–liquid two-phase flow. Furthermore, the effect of water on transient choked flow of supercritical CO_2 pipeline was investigated, and the phenomena of solid particles deposition was captured which was paramount importance of ensuring the safety operation of CO_2 pipelines when throttling by the choke valves.     

Pipe flow of a dense emulsion: Homogeneous shear‐thinning or shear‐induced migration?

The flow field of a 70% concentrated noncolloidal o/w emulsion in a pipe has been investigated by means of Particle Image Velocimetry in a matched refractive index medium. At steady state and in laminar regime, the shape of axial velocity profiles is not parabolic and exhibits a shear‐thinning behavior of the dense emulsion, with a flow index of 0.5 and a negligible yield stress (less than 1 Pa). However, instead of a square root law, the pressure drop increases linearly with U_m. To explain this apparent inconsistency, two mechanisms of different nature are considered. The first originates from a possible relation between the consistency factor and the drop mean diameter. The second mechanism is shear‐induced migration and leads to the development of a concentration gradient in the pipe cross section. Both mechanisms considered reconcile the experimental data, the apparent local shear‐thinning behavior and the linear evolution of the pressure drop with the flow rate. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Modeling of Two‐Phase Flashing Flow of Multicomponent Mixtures in Large Diameter Pipes

A two‐phase flashing flow model is developed to predict the distributions of pressure, temperature, velocity and evaporation rate in a transfer line, which is a typical example of a two‐phase flow pipe in the petrochemical industry. The model is proposed based on the pressure drop model and the multi‐stage flash model. The results indicate that pressure drop, temperature drop, and change of evaporation rate mainly occur in the transition section and the junction site of the transfer line. The predictions of the model have been tested with reliable field data and the good agreement obtained may lead to a better understanding of the two‐phase flashing flow phenomenon, as well as demonstrating the feasibility of applying the model into the design and optimization of pipelines.     

加氢反应气液两相流管路压降计算

炼油化工装置中,存在很多气液两相流管道,任何两相流的管道,都会比单向流时的流动存在很大偏差,从而影响压降的计算。对气液两相流管道压降计算的方法也经历了不同的阶段。加氢反应系统存在很多气液两相流管道,因此找到合适的计算方法是十分必要的。叙述了不同的两相流管道计算方法,选择计算误差更小的Dukler方法进行实例应用,这种方法现在应用的更多更符合工程实际计算结果。     

流化床管式分布器内流场模拟和布气性能分析

以催化裂化装置（FCCU）再生器的管式气体分布器为研究对象,对流化床管式气体分布器的布气性能进行了分析。首先,对气体分布器分支管内的流场进行数值模拟,计算结果表明沿分支管内气体流动方向,压力逐渐增大,截面流量逐渐减少,沿程喷嘴流量逐渐增大;同时分支管上游入口还存在着明显的偏流现象,从而导致了上游喷嘴的出口流量小于设计流量,下游喷嘴的出口流量高于设计流量,造成流化床内非均匀布气。然后,依据分支管的变质量流动特点,将一般变质量流动的动量方程用于分析分支管内的流动过程,表明分支管的流动过程属于“动量交换控制模型”,具有始端静压低末端静压高的特点,固有压力分布不均匀的特征。这种不均匀的压力分布导致了喷嘴布气不均匀和磨损等系列问题。最后,结合流化床内的压力特点,综合分析气体分布器的分支管压降和喷嘴压降,明确了喷嘴出口流量与分支管压力分布的关系,喷嘴临界压降与设计压降的关系,结论表明分支管的结构改进可以优化和改善分布器的布气性能。     

A new mechanistic model to predict gas–liquid interface shape of gas–liquid flow through pipes with low liquid loading

Devising a new mechanistic method to predict gas–liquid interface shape in horizontal pipes is concerned in this article. An experiment was conducted to find the pressure gradients of air–water flow through a 1‐in. pipe diameter. Comparing results of model with some experimental data available in the literature demonstrates that the model provides quite better predictions than existed models do. This model also predicts flow regime transition from stratified to annular flow better than Apparent Rough Surface and Modified Apparent Rough Surface models for both 1‐ and 2‐in. pipe diameters. The model also leads to reliable predictions of wetted wall fraction experimental data. Although one parameter of new model was evaluated based on air–water flow pressure loss experimental data for 1 in. pipe, it was considerably successful to predict pressure drop, liquid holdup, stratified‐annular transition and wetted wall fraction for other gas–liquid systems and pipe diameters. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1043–1053, 2015     

Prediction of Two‐Phase Frictional Pressure Drop for the Concurrent Gas and Newtonian Liquids Upflow through Packed Beds

Correlations were developed to predict frictional pressure drop for concurrent gas‐liquid upflow through packed beds covering all the three identified flow regimes, i.e. bubble flow, pulse flow and spray flow. The observation that the gas and liquid flow rates have different influences on the two‐phase pressure drop in different flow regimes, was taken into consideration in the development of these correlations. More than 600 experimental pressure drop data from the present study and literature covering a wide range in gas‐liquid systems, flow rates and column packing were used.     

基于OLGA的起伏湿气集输管道水力特性研究

由于多相流动的经济性,气田大部分集输管道都采用气液混输技术。集输管线在通过地形起伏的地区时,气体的压力、温度及流速将随之变化,地形起伏不均是造成气田气液混输管道生产不稳定的一个重要因素。采用多相流模拟软件OLGA建立了湿气集输管道水力计算模型,模拟分析了地形起伏程度、管道输气量、管径、含水率对管道压降的影响。并对不同影响因素下的模拟结果进行分析,该分析结果为地形起伏地区气田集输管道的运行管理和设计提供了理论基础。     

Bifurcation analysis of index infinity DAE parabolic models describing reactors and reacting flows

We show that most steady‐state models of chemical reactors and reacting flows in which convection effects are dominant and diffusion/conduction is neglected in the flow direction but included in the transverse directions, may change from parabolic type with a unique solution to index infinity differential‐algebraic equation (DAE) type with an infinite number of steady‐state solutions depending on the values of the reaction parameters. When a model is of index infinity, standard numerical methods may find only one of the solutions corresponding to latest possible ignition. We present complete bifurcation analysis of these models, a method for finding all solutions, determine the stability and, for some simpler cases, the domain of initial conditions attracted to these states. We also demonstrate that the various steady‐state solutions of the DAE systems are best found by integrating the transient hyperbolic versions of the models with appropriately selected capacitance terms and initial conditions. © 2016 American Institute of Chemical Engineers AIChE J, 63: 295–305, 2017     

START-UP FLOW IN A PIPE FOLLOWING THE SUDDEN IMPOSITION OF A CONSTANT FLOW RATE

The transient flow in a long pipe following the sudden imposition of a constant flow rate is considered. An exact analytical solution of the axisymmetric Navier-Stokes equations in terms of an infinite series of Bessel functions is derived. Time-dependent velocity profiles, as well as time histories of the axial pressure-gradient and the wall-friction, are presented. It is observed that the start-up time required to reach steady state is significantly shorter than if the start-up flow results from a suddenly imposed constant pressure gradient. The “Annular Jet Effect” observed experimentally by Kataoka et al. (1975) is not exhibited by the present solution.     

排气管偏置分离器分离性能的数值模拟

采用雷诺应力模型（Reynolds stress model,RSM）对旋风分离器排气管中置和偏置时的气相流场进行了数值模拟,并用拉格朗日法模拟了分离器内颗粒的运动轨迹。气相流场模拟结果与实验结果吻合得较好。结果表明：排气管偏置后,分离器内沿排气管偏置方向的切向速度有所提高,排气管下部短路流较小,颗粒离心运动更加强烈,提高了分离效率的同时压降变化不大,分离器经济性更好。     

Pressure Drop Models for Gas/Non‐Newtonian Power‐Law Fluids Flow in Horizontal Pipes

Models commonly used in literature are evaluated versus 696 data points to predict the pressure drop of gas/non‐Newtonian power‐law fluids flow in horizontal pipes. Suitable models are recommended. A new correlation is developed by ignoring the pressure drop across the gas slug and adopting the liquid slug holdup of gas/non‐Newtonian fluid flow into the homogeneous model. The theoretical curves can capture the test data trends and the overall agreement of predicted values with experimental data is sufficient to be practically applied in industry.     

Settling and re‐entrainment of wax particles in near‐gelling systems

Under near‐gelling conditions, the precipitated wax particles can settle down due to gravity and form a bed at the bottom of the pipeline. During restart, the settled waxy bed can increase the pressure drop significantly, and the necessity for pigging and/or addition of chemicals has to be determined to re‐entrain settled wax particles. A laboratory‐scale flow loop, first of its kind, has been built and used to understand the settling and re‐entrainment behavior. The experimental results confirmed the settling of precipitated wax in a pipe under quiescent conditions when the oil temperature falls between wax appearance temperature and pour point. During restart, complete re‐entrainment was attained after reaching a critical flow rate. Solid transport models were able to predict reasonably good results in agreement with experiments. This work emphasizes the importance of understanding the behavior of waxy crude oil during production shutdown and design appropriate startup strategies. © 2017 American Institute of Chemical Engineers AIChE J, 64: 765–772, 2018     

Integrated simulations of structural performance,molding process,and warpage for gas‐assisted injection‐molded parts. III. Simulation of cyclic,transient variations in mold wall temperatures

Whether it is feasible to perform an integrated simulation for structural analysis, process simulation, as well as warpage calculation based on a unified CAE model for gas‐assisted injection molding (GAIM) is a great concern. In the present study, numerical algorithms based on the same CAE model used for process simulation regarding filling and packing stages were developed to simulate the cooling phase of GAIM considering the influence of the cooling system. The cycle‐averaged mold cavity surface temperature distribution within a steady cycle is first calculated based on a steady‐state approach to count for overall heat balance using three‐dimensional modified boundary element technique. The part temperature distribution and profiles, as well as the associated transient heat flux on plastic–mold interface, are then computed by a finite difference method in a decoupled manner. Finally, the difference between cycle‐averaged heat flux and transient heat flux is analyzed to obtain the cyclic, transient mold cavity surface temperatures. The analysis results for GAIM plates with semicircular gas channel design are illustrated and discussed. It was found that the difference in cycle‐averaged mold wall temperatures may be as high as 10°C and within a steady cycle, part temperatures may also vary ∼ 15°C. The conversion of gas channel into equivalent circular pipe and further simplified to two‐node elements using a line source approach not only affects the mold wall temperature calculation very slightly, but also reduces the computer time by 95%. This investigation indicates that it is feasible to achieve an integrated process simulation for GAIM under one CAE model, resulting in great computational efficiency for industrial application. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 339–351, 1999     

Dynamic modeling and simulations of the behavior of a fixed‐bed reactor‐exchanger used for CO2 methanation

A multidimensional heterogeneous and dynamic model of a fixed‐bed heat exchanger reactor used for CO₂ methanation has been developed in this work that is based on mass, energy and momentum balances in the gas phase and mass and energy balances for the catalyst phase. The dynamic behavior of this reactor is simulated for transient variations in inlet gas temperature, cooling temperature, gas inlet flow rate, and outlet pressure. Simulation results showed that wrong‐way behaviors can occur for any abrupt temperature changes. Conversely, temperature ramp changes enable to attenuate and even fade the wrong‐way behavior. Traveling hot spots appear only when the change of an operating condition shifts the reactor from an ignited steady state to a non‐ignited one. Inlet gas flow rate variations reveal overshoots and undershoots of the reactor maximum temperature. © 2017 American Institute of Chemical Engineers AIChE J, 64: 468–480, 2018     

段塞流的流量瞬变特性试验研究

An investigation of the characteristics of flowrate transients within slug flow was conducted in a largescale outdoor testing facility.The test section consisted of a 378m long,7.62cm diameter stainless steel pipe. Air and water were used as the test fluids.The response to a change of flowrate o either phase or two phases was measured using a series of pressure transducers and differential pressure transducers.An increase or decrease in gas flowrate caused a pressure overshoot above the value at new steady state or led to a pressure undershoot to form a temporary stratified flow.Pressure waves existed in the pipeline,spreading from the entrance to the exit.The magnitude of pressure overshoot in “up-gas”transient or of pressure undershoot and period of the temporary stratified flow in “Down-gas” transient are related to the change of gas flowrate and the distance away from the entrance.In contrast,the change in liquid flowrate was accommodated by smooth transitions between the corresponding steady states,and only one obvious change was found in the slug frequency.According to experimental results,the pressure overshoot,pressure undershoot and the pressure wave propagation were analyzed,and the phenomena were explained reasonably.Some correlations for the calculation of the pressure overshoot and undershoot were proposed.     

Experimental test of a model for laminar slurry flow with sedimentation

The ability of a flow-sedimentation model to simulate the flow of a slowly-settling suspension being transported in the laminar regime through a pipeline with a constant overall pressure drop imposed on it was assessed using experimental scaled-down pipeline data. Comparison of predicted volumetric flow rate versus time profiles to those observed suggested that the blockage process took place in two steps. Initially, a sediment grew on the lower pipe wall and the flow gradually lessened, as was modelled. As the flow slowed down, ultimately a plug, which enclosed the full cross-section of the pipe, formed and lead to the rapid blockage of the pipe. It was envisioned that the granular properties of the concentrated suspension became dominant during the final blockage process. A deposit velocity criterion was also developed from the flow-sedimentation model and was used to generate a deposit velocity versus pipe diameter plot. Results from the plot indicate that the laminar pipeline flow of a slowly-settling suspension is possible in small diameter pipes.