Movement of Concentration Pulse — Lesson 3

This lesson covers the concept of flow through porous media, focusing on miscible displacement, where a fluid is injected into a porous medium already containing a fluid. The lesson explains how mixing occurs in a capillary, discussing Taylor dispersion and how non-uniform velocity profiles contribute to mixing. The lesson also explores the impact of diffusivity on the broadening of the fluid and the role of the Taylor dispersion coefficient in stretching the fluid. The lesson concludes by introducing the concept of a step change in concentration and how it affects the concentration profile. For instance, if a step change in concentration is introduced at the inlet of a capillary, the concentration profile at the outlet will be diffused rather than a firm step change.

Video Highlights

00:44 - Understanding mixing in a capillary and Taylor dispersion
03:18 - Role of Taylor dispersion coefficient in fluid stretching
23:17 - Introduction to step change in concentration
29:38 - Effect of step change on concentration profile

Key Takeaways

- Miscible displacement involves injecting a fluid into a porous medium already containing a fluid, leading to mixing.
- Taylor dispersion, caused by non-uniform velocity profiles, contributes to the mixing process.
- The diffusion coefficient or diffusivity impacts the broadening of the fluid. Higher diffusivity leads to faster broadening.
- The Taylor dispersion coefficient plays a crucial role in stretching the fluid. Higher average velocity or larger capillary radius leads to more stretching.
- Introducing a step change in concentration at the inlet of a capillary results in a diffused concentration profile at the outlet due to mixing.