【作者】 刘夷平；

【导师】 王经；

【作者基本信息】 上海交通大学 ， 工程热物理， 2008， 博士

【摘要】 油气混输技术以其高效率、低成本、环境适应性强等特点受到石油工业的广泛重视。工程上的油气混输系统,由于受流量、介质物性、管道形式以及倾斜角度等因素影响,截面含气率发生变化,导致管内出现各种流型。如何预测段塞流的出现,是油气混输工程的关键技术之一,也是两相流科学的重要理论问题之一。随着气液两相体积流量的变化,气液界面呈现出不同的状态和特性,特别是当流型发生转换时,气液界面特性对于预测流型转换的临界条件有较大的影响。一方面,液相表面的波动使得气液两相间出现粗糙的界面,另一方面,从管道轴向方向观察,液层不再是平整的表面,而是随着气相速度的增加发生弯曲变形。因此,本文对水平油气两相流流型转换及其相界面特性进行了以下五个方面的研究1.自行搭建了管径25.4 mm油气两相流实验装置,对水平油气两相流流型及其转换特性,特别是层状流向段塞流的转换影响因素进行了实验研究。实验中观察到光滑分层流、波状分层流、泡状流、段塞流和环状流。根据实验数据绘制了流型图,并确定了流型转换边界。2.在前人研究工作基础上,应用一维波模型和段塞稳定性模型,对油气两相流出现段塞流时的各相临界表观速度和临界液层高度进行了理论预测。计算结果表明,两种模型分别适用于不同的流速区域,在较低的气相流速下,一维波模型的预测结果比较理想,但是不适用于较高的气相流速区域。利用段塞稳定性模型可以较好地获得高流速下分层流向段塞流的流型转换条件。因此,本文结合这两种模型对发生流型转换时的临界参数进行了分析。3.根据各种流型的相分布特征,使用简化的两流体模型预测流型转换以及相应的临界参数。计算结果突出了摩擦因子本构关系在两流体模型中的重要性,本构关系的准确性影响流型转换和理论模型的预测效果。根据实验结果,对气液界面剪切应力进行了不确定度分析,结果表明气壁剪切应力预测的不确定度在整个界面剪切应力不确定度中所占比重较小。以气壁摩擦因子为基准,通过动量平衡法间接得到界面剪切应力或界面摩擦因子。特别在流型转换的预测中,动量平衡法相对于一般经验关系式得到的结果更为准确。4.对圆管内充分发展气液波状分层流进行了数值模拟。使用两层湍流模型对稳态轴向动量方程进行了数值求解。在双极坐标系内,利用有限体积法对控制方程离散求解。借鉴单相管流的处理方法,将气液界面视为粗糙平面,并引入等效砂砾粗糙度的概念来考虑气液两相的相互作用。对比分析表明,该计算方法不仅相对于一般光滑界面模型提高了预测的准确度,而且证明了气液界面摩擦本构关系对于流型转换和理论分析的重要性。5.低持液率气液两相流常见于天然气输运工程。在气速较低区域,气液界面粗糙度不均匀分布,导致气相区域出现二次流。二次流的形成是气液界面下凹的主要原因;在较高的表观气速区域,界面形状、界面粗糙度和液滴的携带/沉积机理有关。据此,在两流体模型的基础上,建立了有关界面曲度和界面摩擦因子的本构关系式。计算结果和实验数据进行的对比分析表明,应用新的关系式有效地改善了持液率和压力梯度的理论预测效果。更多还原

【Abstract】 Oil-gas mixing transportation technology plays an important role with its characteristics of high efficiency, low cost and wide applicability in oil industry. The system of the oil-gas transportation, which is affected by the flux, the fluid physical properties, the geometry of the pipeline, the inclination angle and so on, makes the change of the void fraction, and shows different kinds of flow pattern. As a typical two-phase flow problem, the nature of horizontal oil-gas transient flow in pipes is studied from a flow pattern perspective.By detailed analysis and using a methodology developed specifically for this study, the observed flow patterns were classified into stratified smooth, stratified wavy, bubbly, slug, and annular flow regimes. The physical mechanisms that govern the transition between stratified and slug flow were identified and discussed. Based on the experimental data obtained in this study and on comparison with published flow regime maps, a flow regime map was presented to predict the prevailing flow regime for oil-gas flows in small diameter horizontal pipe at near-atmospheric conditions. The boundaries of the regimes were represented by transition bands.A theoretical approach which is based on one-dimensional wave model combined with slug stability model was presented to predict transition from the stratified patterns to slug flow. Data confirming the validity of the approach were generated from a self-built 25.4 mm diameter horizontal oil-gas pipeline in SJTU. The experimental data obtained in a 50 mm diameter horizontal oil-gas pipeline in Zhejiang Univ. were also analyzed. The comparison showed that these two models are applicable for different ranges of gas flows respectively. At low gas velocities, one-dimensional wave model works well, but is not suitable for high gas flows in which slug stability model provides better prediction of the critical liquid heights and the critical superficial velocities for the transition to a slug flow.Based on the observed disposition of the phases in each flow regime, simplified two-fluid models were used to predict flow regime transition or critical parameters such as superficial velocities and liquid holdup. Results clearly showed that the interactions between the phases at the interface have considerable effects on the velocity profiles within the phases such that, in general, the conventional definitions of the friction factors are invalidated. The measured liquid holdup and pressure gradients were used to obtain the interfacial friction factors for corresponding flow regime. A framework for the correlation of the deduced interfacial shear stress was presented from the experimental measurement. The uncertainty analysis was used to show that the measured liquid holdup and the calculated gas-wall shear stress by Blasius equation did not significantly influence the overall results, while the existing correlations might lead to large uncertainties, irrespective of accuracy of the experimental data or the appropriateness of the correlating technique.To evaluate the interactions between the phases at the interface, a numerical modeling of fully developed stratified wavy gas-liquid pipe flow in circular cross-section pipe was presented. Two-dimensional, steady-state axial momentum equations were solved with a two-layer turbulence model. The governing equations were discretized using a finite volume method on a bipolar coordinate system. Given longitudinal velocity profiles in the gas and assuming a logarithmic law above the waves, the simulations validated the concept of interfacial roughness to account for gas-liquid interactions.The region finally investigated was that of flows with relatively low liquid loading. Such flows are typically experienced in gas-condensate lines in oil industry. At low gas velocities, the interface curvature is dominated by the secondary flows, which is attributed to the non-uniformity of the interfacial roughness experienced by the flow of the turbulent gas-phase, at high gas velocities, the process of entrainment and deposition is the dominant contributor to the liquid phase transfer to the upper part of the pipe wall. A two-fluid model was employed for low liquid loading flows. New correlations were proposed for the interfacial curvature and the interfacial friction factor. The effect of droplet entrainment on the interfacial friction factor was also accounted for. The predictions of liquid holdup and pressure gradient from the new correlations matched well with the reported experimental data.更多还原