I need to find what is multiscale Chapmann enskog, How it is used. what is basic difference between simple and multiscale expansion and how it related the macroscopic information with microscopic level…

Hi adnan,
You can find the details of Chapman-Enskog expansion or multi-scale expansion in this book:

“Lattice gas cellular automata and lattice Boltzmann models : An introduction”
Dieter A. Wolf-Gladrow

Or you can download Dr. Latt’s thesis (recommended; clearer and simpler notation).

Good luck!