Calculating Diffusion Speed from Gas to Vacuum: How Do You Do It?

[zhaoxh]

Hi everyone,
I'd like to ask you a question. How to calculate the diffusion speed from a bulk of gas with density of n to vacuum? Thank you!

 

[edgepflow]

I would start with Fick's Law.

 

[Dickfore]

What is diffusion speed?

 

[zhaoxh]

What is diffusion speed?

actually, I want to consider the follow case. Consider that a bullet crosses a bulk of gas (desity=n), how to calculate the density evolution (with time) within the channel after the bullet goes through the gas.