扩散限制聚集与粘性指化图案的模拟研究

扩散限制聚集与粘性指化图案的模拟研究顾健德，田安民，鄢国森（四川大学化学系，成都，６１００６４）关键词ＤＬＡ，粘性指化，计算机模拟大自然经常以非常奇妙的方式向人们展示其魅力，吸引人们不断去思考和探索．四川大学图书馆文献阅览室的玻璃顶棚上出现的粘性指化...     

聚丙烯酰胺水溶液的流变性质

粘性指进现象;聚丙烯酰胺水溶液的流变性质     

How to predict viscous fingering in three component flow

In a WAG process (Water Alternate Gas), water and a miscible solvent (gas) are injected into a reservoir containing water and oil. The solvent will finger through the oil, leading to early breakthrough and poor recovery. Compared with a miscible flood, when only solvent is injected, fingering is supressed by the simultaneous injection of water, since this reduces the apparent mobility contrast between the injected and displaced fluids. The fingering in a miscible flood, with only hydrocarbon flowing, can be modelled successfully using a Todd and Longstaff fractional flow. In this paper, we demonstrate how to modify the effective Todd and Longstaff mobility ratio self-consistently to account for fingering in three component systems. The resultant empirical equations of flow are solved exactly in one dimension and are in excellent agreement with the averaged saturation and concentration profiles computed using two dimensional high resolution simulation, for a variety of injected water saturations, in both secondary and tertiary displacements.     

Axisymmetric three-dimensional finger solutions in Mullins-Sekerka equation

In this paper, we study the existence problem of axisymmetricthree-dimensional finger solutions of Mullins–Sekerkaequation. The finger solutions are travelling wave solutionswhose finger-shaped interfaces are moving along a certain directionat a constant speed within a cylindrical domain. The existenceof at least one axisymmetric three-dimensional finger solutionis obtained through a fixed-point argument of the Hilbert transformation.     

Fingering patterns on an expanding miscible drop in a rotating Hele‐Shaw cell

We perform a detailed numerical study for the evolution of an expanding miscible drop in a rotating Hele‐Shaw cell. Two mathematical formulations applied to model the coating layer expansion during practical spin‐coating process, such as thinning of the layer by cell pressing and drop spreading outward due to injection, are investigated. Including miscible interfacial stresses, we focus on the investigation of dynamical and morphological influences of two different stabilizing parameters: the gap width parameter for the pressing cell and the injecting strength. In the case of a pressing cell, the fingering features of the expanding miscible drop, such as the critical radius, are distinct from those ones in the experiments of spin coating due to the different distributions of the inherent radial velocity. On the other hand, the global interfacial evolutions of an expanding drop with an additional injection bear remarkable resemblances to their immiscible counterparts. The better agreement for an injecting model suggests its appropriateness when we simulate the emerging fingering instabilities in the spin‐coating process. Moreover, we investigate the effects of Coriolis force at higher miscible Bond numbers. Coriolis force affects significantly the onset of fingering instability and the tilting angles of fingers. These stable effects are in line with the results from the previous studies for miscible and immiscible flow fields. Copyright © 2007 John Wiley & Sons, Ltd.     

黏性指进的实验与模拟

利用简易装置观察了黏性指进现象,使用照相机拍摄多种黏性指进分形图形,测量了分形维数,并采用数值模拟中的随机模拟演示了黏性指进图形.     

聚合物流体渗流机理研究

聚合物流体在多孔介质中渗流的研究是近年来有重大进展的领域。本文介绍从力学与物理方法进行渗流机理研究的思路、主要结果和当前活跃的研究课题。流体的非牛顿性对复杂边界条件下均匀流体力学效应的影响已得到了较好的定量处理;揭示了拉伸流粘弹特性对渗流影响的机理,其定量描述则尚有待努力。进而讨论了石油工程中十分重要的非均一流体渗流的新进展,包括大分子效应与粘性指进效应及其分形描述。对于上述物理效应的综合考虑将使聚合物渗流力学研究进入新的阶段。      

用聚丙烯酰胺水溶液驱替油溶液的粘性指进现象的研究(Ⅰ)

流度比;驱油溶液;用聚丙烯酰胺水溶液驱替油溶液的粘性指进现象的研究(Ⅰ)     

Displacement of yield-stress fluids in a fracture

We consider a displacement of several yield-stress fluids in a Hele-Shaw cell. The topic is relevant to the development of a model for the flow of multiple phases inside a narrow fracture with application to hydraulically fracturing a hydrocarbon-bearing underground formation. Existing models for fracturing flows include only pure power-law models without yield stress, and the present work is aimed at filling this gap. The fluids are assumed to be immiscible and incompressible. We consider fluid advection in a plane channel in the presence of density gradients. Gravity is taken into account, so that there can be slumping and gravitational convection. We use the lubrication approximation so that governing equations are reduced to a 2D width-averaged system formed by the quasi-linear elliptic equation for pressure and transport equations for volume concentrations of fluids. The numerical solution is obtained using a finite-difference method. The pressure equation is solved using an iterative algorithm and the Multigrid method, while the transport equations are solved using a second-order TVD flux-limiting scheme with the superbee limiter. This numerical model is validated against three different sets of experiments: (i) gravitational slumping of fluids in a closed Hele-Shaw cell, (ii) viscous fingering of fluids with a high viscosity contrast due to the Saffman–Taylor (S–T) instability in a Hele-Shaw cell at microgravity conditions, (iii) displacement of Bingham fluids in a Hele-Shaw cell with the development of fingers due to the S–T instability. Good agreement is observed between simulations and laboratory data. The model is then used to investigate the joint effect of fingering and slumping. Numerical simulations show that the slumping rate of yield-stress fluid is significantly less pronounced than that of a Newtonian fluid with the same density and viscosity. If a low-viscosity Newtonian fluid is injected after a yield-stress one, the S–T instability at the interface leads to the development of fingers. As a result, fingers penetrating into a fluid with a finite yield stress locally decrease the pressure gradient and unyielded zones develop as a consequence.     

Understanding the importance of the viscosity contrast between the sample solvent plug and the mobile phase and its potential consequence in two-dimensional high-performance liquid chromatography

The effect of solvent viscosity mismatch on elution performance in reversed-phase HPLC was studied using moment analysis. Two conditions were tested: (1) the mobile phase viscosity was less than the injection plug viscosity, and (2) the mobile phase viscosity was greater than the injection plug viscosity. Under the first condition, retention time and elution performance decreased as the viscosity contrast between the mobile phase and injection plug increased. The effect on performance was more marked as the injection volume increased. A decrease in performance of 12% for compounds with retention factors up to 2.8 was apparent even when the viscosity contrast was only 0.165 cP. In the second set of conditions, elution performance was actually observed to increase, by as much as 25% for a 40 μL injection, as the viscosity contrast between the mobile phase and the solute plug increased. No change in the retention factor was observed. This behaviour was attributed to the shape of an injection plug as it enters into the column, whereby a low viscosity plug permeates away from the wall when the column contains a higher viscosity mobile phase, and vice a versa for a high viscosity plug entering a low viscosity mobile phase. At no stage was either a band splitting or shoulders observed with viscosity contrasts up to 1.283 cP, as could have been expected.