1.diffusion of gas：Gas moves in another medium due to concentration gradient. Medium can be another gas (diffusion in this case is called interdiffusion) or a condensable substance.
2.D diffusion coefficient; diffusivity：The ratio of the absolute mass flow rate per unit area to the normal concentration gradient per unit area is obtained.China PVD Plating Machine Suppliers
3.viscous flow：The average free path of gas molecule is much smaller than the minimum cross-section size of the duct. Therefore, the flow depends on the viscosity of the gas, which can be laminar or stagnant.
4.η viscous factor：The ratio of tangential force to velocity gradient per unit area in the direction of airflow velocity gradient.
5.sorption：The trapping of gas or vapor (adsorbate) by solid or liquid (adsorbent).
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