依时性流体圆管法非稳态阶段流变测试的可靠性研究

Reliability of rheology tests using circular tube has not been proved considering deviation of measurement caused by unsteady flow of the testing fluid in the tube. In this research, changing rules and essential reasons of measurement deviation caused by the transient flow of testing fluid in circular tube will be investigated. Based on the expected achievements, we aimed to enrich the fundamental theory and enhance the applicability of measuring method using circular tube. .Considering velocity distribution of testing fluid, mathematical models of incompressible flow of time-dependent rheological fluid in circular tube will be established by combining constitutive equation and momentum equation. Based on the measuring principle of circular tube, measuring deviation caused by unsteady velocity distribution will be discussed, and a simplified momentum equation will be proposed. .Considering the compressibility of testing fluid, one-dimensional numerical model for compressible flow will be proposed using the simplified momentum equation and continuity equation for discussing the deviation caused by fluid compressibility. Considering the volume void caused by volume shrinkage as a result of gelled structure formation of the testing fluids, a boundary condition expressed as dynamic pressure interface will be introduced to the numerical model. Based on the numerical model, measuring deviation caused by the volume void of fluid will be discussed. From the discussion, a quantitative relationship among tube pressure, shear stress on the inner surface of tube and pressure wave will be proposed. .Further study will be carried out taking gelled crude oil as an example. Rheological properties of gelled crude oil will be tested using rheometer. Compressibility and volume void ratio will be calculated in self-developed instruments. Based on the parameters’ magnitude of these properties of gelled crude oil, influence order of the factors that leads to the deviation will be determined. Finally, a reliable measuring and calculating method for the rheological properties of gelled crude oil in a circular tube will be proposed.

因非稳态流动产生的偏差导致圆管法测试依时性流体流变性的可靠度存疑。本课题拟开展非稳态流动对圆管法流变测试结果的影响规律与机理研究，以期完善圆管法流变测试的理论基础、拓展其适用范围。.考虑圆管径向速度分布，结合流体本构方程与动量方程，建立依时性流体的不可压缩非稳态圆管流动模型；结合圆管法流变测算准则，分析非稳态速度场引起的圆管法流变测量偏差，合理简化，构建一维动量方程。引入流体的可压缩性，结合简化动量方程与连续性方程，建立依时性流体可压缩一维圆管流动模型，探索压缩性引起的圆管法测量偏差。考虑体积收缩所致裂隙，引入动态压力界面边界，建立含裂隙流体非稳态一维圆管流动模型，分析裂隙度对依时性流体圆管法测试结果的影响，量化圆管压力与壁面剪切力的关系。以凝胶态原油为研究对象，获取其流变性、压缩性与裂隙度等参数量级，分析圆管法测试原油流变性时各影响因素的主次关系，形成圆管法测算原油管流特性的可靠方法。

圆管法是重要的流变测试手段之一。由于初始非稳态流动的影响，基于圆管法测试获取的依时性流体初始流变数据结果可靠性存疑。本课题从圆管非稳态速度分布、流体可压缩性等角度讨论了圆管初始非稳态流动对流变测试结果的影响机制。.开展了牛顿流体与Cross触变流体、Burgers粘弹性流体、粘弹-触变流体等依时性流体的非稳态不可压缩圆管流动研究，讨论了非稳态速度场对各类流体圆管法流变测试结果的影响规律。结果显示，各类流体在圆管内的非稳态速度场均会对圆管法流变测试结果产生影响，粘弹性特征流体还会出现初始震荡现象，随着测试时间的延长，速度场充分发展，该影响逐渐消失；流体表观流动性越差、圆管管径越小，圆管速度场充分发展时间越短，且控制速度入口边界条件下充分发展时间短于控制压力入口边界条件。.以胶凝原油为例开展依时性流体压缩性研究，发现其表现出显著的依时性体积压缩特征。构建了一维圆管可压缩流动模型，并耦合动态压力界面，建立了含空隙依时性流体一维圆管非稳态流动模型，研究发现流体可压缩性越大、内部空隙率越高，胶凝原油非稳态圆管流动过程中压力传播速度越慢，圆管轴向流动差异越明显。.通过胶凝原油圆管非稳态流动实验测试发现，圆管入口压力越低，圆管轴向流动一致性越强，即当利用圆管法获取胶凝原油管道临界启动工况下的数据时，圆管法的测试结果具有可靠性。.通过论证非稳态速度场和流体可压缩性对依时性原油圆管非稳态流动力学特性的影响，合理简化，建立了适用于工业依时性原油管道非稳态流动与传热的数学模型，实现了热含蜡原油管道安全停输临界状态下的再启动热力、水力计算。