1. 大学物理（热学） Mean Free Path Diffusion, Thermal conductivity, and Viscosity

2. Equilibrium distribution
ni  the number of molecules of
dn is the number of molecules
vy vy + dvy in
near v

3. Meaning of dn/N
among N molecules, how many are near v
probability that one molecule is near v
proportional to dvx ...

4. The probability should be normalized
Isotropic assumption
The solution is
The probability should be normalized
Normalization is not necessary but conventional.

5. each normalized a a 12

6. Known
while

7. For unit volume
Maxwell velocity distribution

8. Maxwell speed distribution
Most probable speed
For one molecule, what speed is most possible?
Among N molecules, what is the speed most molecules have in unit interval?

9. Maxwellian can be written as

10. The average speed

16. Transport phenomena
Heat transfer :
conduction convection thermal radiation
diffusion
viscosity
thermal conductivity
Conduction
Fourier’s law

17. Diffusion
Fick’s law
Viscosity 6

18. Microscopic theory of transport coefficients

19. For mass transport,

20. Similarly

21. Hydrogen under STP
r = 1.12×10−10m

22. Experimental results: