4.3. General Expression for Effective Diffusivity

Try these first

1. 1.

   What is effective diffusivity (DA3)?

   Hint

   Think about how substances migrate through different materials.

2. 2.

   Define porosity.

   Hint

   It relates to how much space exists within solids.

3. 3.

   What does DA3 represent in diffusion studies?

   • Concentration
   • Effective diffusivity
   • Porosity

   Hint

   Think of it as the rate of movement through porous materials.

4. 4.

   True or False: Higher porosity increases diffusion rates.

   • True
   • False

   Hint

   Relate this to paths available for substances.

5. 5.

   A contaminated site has a porosity of 0.25 and an effective diffusivity of 2.5e-5 m²/s. If the retardation factor is 1.5, calculate the rate of contaminant movement over time.

   Hint

   How does the retardation factor influence the overall migration speed?

6. 6.

   Assuming a linear concentration gradient exists across a distance of 4 meters with a given effective diffusivity of 1.2e-4 m²/s. How long will it take for the substance to cover this distance?

   Hint

   What is the formula for time based on distance and diffusivity?