Add a new method of calculating binary diffusivity
- Chapman-Enskog method
- Changed the usage of exterdiff.m file

Signed-off-by: Peng Dai <kpd337@gmail.com>
Modified the experimental data
- Adjusted the time span of the data

Signed-off-by: Peng Dai <kpd337@gmail.com>
Modified ErgunT
- Plot intrinsic rate vs T and rate vs gas concentration

Signed-off-by: Peng Dai <kpd337@gmail.com>
Regular change

Signed-off-by: Peng Dai <kpd337@gmail.com>