4.2.2. Internal Porosity and Complications in Diffusion

Try these first

1. 1.

   What is the effective diffusivity and why is it important?

   Hint

   Think about how solids affect diffusion.

2. 2.

   Explain what porosity means in the context of diffusion.

   Hint

   Consider how space in materials helps fluid movement.

3. 3.

   What does effective diffusivity refer to?

   • Speed of diffusion in vacuum
   • Diffusion through porous materials
   • Rate of flow in liquids

   Hint

   Think about how solids change the path of diffusion.

4. 4.

   True or False: The local equilibrium assumption implies that diffusion and adsorption rates are different.

   • True
   • False

   Hint

   Are diffusion and adsorption happening at the same speed?

5. 5.

   Given a scenario of a pollutant spreading in a sandy soil with high porosity, calculate the expected time for diffusion considering effective diffusivity. Assume DA3 = 0.045 m²/s.

   Hint

   Consider time = distance² / (2 * DA3) for estimating.

6. 6.

   In a site with significant heavy metal adsorption onto soil particles, evaluate how this might change diffusion rates compared to a clean sandy substrate.

   Hint

   Examine how adsorption directly affects the movement of contaminants.