A simple case of laminar flow passing a plate is shown in Fig. 3.34. The velocity of flow near plate is very small and this results in a stagnant layer. The gas can diffuse through stagnant layer to surface. The mass transport depends fundamentally on reactant concentration, diffusivity and on boundary layer thickness. In terms of experimental parameters it depends on pressure, gas velocity, temperature distribution, reactor geometry and gas properties like viscosity etc.

Fig. 3.35 : Basic model of CVD kinetics