دانلود رایگان مقاله تجزیه و تحلیل سرعت سنجی ذرات جریان دو فاز مخلوط نشدنی در میکرومدل ها

Abstract

We perform micro-PIV measurements in micromodels using very simple optical equipment combined with efficient image acquisition and processing. The pore-scale velocity distributions are obtained for single-phase flow in porous media with a typical pore size of 5–40 µ m at a resolution of View the MathML source vector grid. Because the application of micro-PIV in micromodels is not standard, extensive effort is invested into validation of the experimental technique. The micro-PIV measurements are in very good agreement with numerical simulations of single-phase flows, for which the modeling is well established once the detailed pore geometry is specified and therefore serves as a reference. The experimental setup is then used with confidence to investigate the dynamics of immiscible two-phase flow in micromodels that represent natural complex porous media (e.g., sandstone). For unstable immiscible two-phase flow experiments, micro-PIV measurements indicate that the flow is highly oscillatory long before the arrival of the invading interface. The dynamics are accompanied with abrupt changes of velocity magnitude and flow direction, and interfacial jumps. Following the passage of the front, dissipative events, such as eddies within the aqueous phase, are observed in the micro-PIV results. These observations of complex interface dynamics at the pore scale motivate further measurement of multiphase fluid movement at the sub-pore scale and requisite modeling.

5. Conclusion

We developed and thoroughly validated a micro-PIV system that allows for a better understanding and characterization of the microdynamics of complex flows. The detailed temporal and spatial distributions of the pore-scale velocity field are obtained using simple equipment compared with conventional micro-PIV systems. Thus, these measurements are easily reproducible in any lab. Micro-PIV measurements are performed in micromodels with pore throat sizes less than 10 microns and with a vector resolution of roughly 1μm, for the first time. The experimental measurements are in very good agreement with numerical simulations of steady single-phase flow for which the numerical models are well established. Thereafter, micro-PIV is used with confidence to investigate immiscible twophase flow properties in porous media with high accuracy. Our first efforts show that we are able to analyze the velocities for unstable immiscible two-phase flows. The micro-PIV measurements during a drainage experiment have already shown unusual behaviors. In particular, for an unfavorable mobility ratio we find that the flow patterns are highly perturbed compared to single-phase flow. Moreover, the flow patterns within the wetting displaced fluid are perturbed before the actual passage of the interface by local and macroscopic effects. In addition, for the first time we were able to quantify the velocity of dissipative recirculations during two-phase flow. These results are potentially important for accurate numerical representation of processes such as CO2 injection into saline aquifers and mixing of CO2 with the resident brine. The observation of these dissipative events opens new lines of research and deserves further experiments and modeling to understand fully their behavior and to characterize their consequences at the different scales. With this experimental device, we can now provide reliable data to validate numerical two-phase flow simulations that are still in development.