基于分散相阻碍和Gibbs自由能变化的油包水乳状液蜡分子扩散微观机理及其量化表征

Wax diffusion in water-in-oil emulsion is a complicated mass transfer process involving basic theories of dispersed system, molecular diffusion, heat transfer, phase change and interfacial properties. The research on this issue serves as the basis for the establishment of wax deposition predictive model for water-in-oil emulsion. In this project, three basic scientific problems are put forward focused on the critical role of dispersed water droplets in wax diffusion. From the scientific view，the influences of water volume fraction, droplet size and distribution and interfacial properties on wax diffusion process will be studied experimentally and theoretically. The 3D microstructure model of water-in-oil emulsion will be proposed by focused beam reflectance measurement and particle video microscope. The blockage degree of dispersed droplets on wax diffusion path will be quantified with geometrical analysis method and verified by nuclear magnetic resonance spectrometry. The variation of Gibbs free energy of emulsion system will be calculated according to phase transition thermodynamics and heterogeneous nucleation theories. Compared with differential scanning calorimetry test results, the effects of dispersed phase and oil-water interface characteristics on wax saturation concentration and its mechanism will be explored. Wax diffusion experiments under static condition will be conducted on a new experiment platform and the temperature field variation will be simulated with computational fluid dynamics software to reveal the relation of wax diffusion rate with temperature field and wax concentration field. Based on all these outcomes, a model to calculate the effective diffusion coefficient of wax molecules in water-in-oil emulsion will be put forward. This will provide a sound foundation for the wax deposition prediction in water-in-oil emulsion, and contribute to the safety and economic operation of multiphase flow pipelines.

油包水乳状液的蜡分子扩散是一个复杂传质过程，涉及分散体系、分子扩散、传热、相变和界面性质等诸多基础理论，对它的研究是实现油包水乳状液蜡沉积预测的前提。本项目基于分散相在蜡分子扩散中的关键作用，提炼出基础科学问题，实验研究和理论分析分散相粒径分布、界面性质等因素对蜡分子扩散的影响。本项目通过聚焦光束反射测量技术和可视化手段构建油包水乳状液三维微观结构模型，结合几何分析法和核磁共振技术探索分散相粒径分布对蜡分子扩散路径的阻碍作用；引入相变热力学和非均匀成核理论计算体系Gibbs自由能变化，对比差示扫描量热技术测试结果，揭示分散相和油水界面性质对蜡组分饱和浓度的影响机理；搭建蜡分子静态扩散实验平台，结合计算流体力学软件模拟，阐明蜡分子扩散速率与温度场、蜡分子浓度场的关系，建立油包水乳状液蜡分子扩散系数计算模型，为油包水乳状液蜡沉积预测提供理论基础，为保障多相流管道的安全经济运行作出贡献。

油包水乳状液的蜡分子扩散是一个复杂传质过程，涉及分散体系、分子扩散、传热、相变、界面性质等诸多基础理论，对它的研究是实现油包水乳状液蜡沉积预测的前提。本项目基于分散相在蜡分子扩散中的关键作用，提炼出基础科学问题，实验研究和理论分析分散相粒径分布、界面性质等因素对蜡分子扩散的影响。本项目通过聚焦光束反射测量技术和显微观察法构建了油包水乳状液三维微观结构模型，采用Rosin-Rammler分布模型定量描述了乳状液分散相粒径的累积频率分布。结合几何分析法推导了乳状液蜡分子扩散路径的迂曲度，提出了分散相阻碍作用系数计算公式，并采用核磁共振技术进行了验证，不仅可以体现含水率对扩散路径阻碍作用的影响，还能够量化分散相平均粒径和粒径不均匀性的影响。引入相变热力学和非均匀成核理论计算体系Gibbs自由能变化，与差示扫描量热法测试结果进行对比，根据含水率、比表面积等特征参数对过冷度的影响规律，从结晶完整性、晶粒尺寸分布、成核位置数量变化等角度阐明水相对乳状液过冷度的影响机理。油-水界面可以为蜡分子的非均匀成核提供条件，从而提高了蜡结晶的温度，相同温度下形成的蜡晶量也更多。提出了通过折射率法测试析蜡温度的方法，能够得到可靠的结果，操作简单，并具有较高的稳定性和灵敏性。搭建了蜡分子静态扩散实验平台，开展了不同条件下的蜡分子扩散实验，结合计算流体力学软件模拟，阐明了蜡分子扩散速率与温度场、蜡分子浓度场的关系，温度分布可以从蜡分子浓度梯度、参与扩散总量和热运动等方面影响蜡分子扩散速率；扩散速率的变化会直接影响蜡沉积物导热系数，进而影响温度分布。建立油包水乳状液蜡分子扩散系数计算模型，考虑了扩散过程中蜡分子扩散速率、溶解度和温度梯度随时间的变化，结果比常规方法得到的扩散系数更加接近计算条件下的实际扩散情况。研究成果为油包水乳状液蜡沉积预测提供了理论基础，可以为保障多相流管道的安全经济运行做出贡献。