This paper describes the growth mechanism and the characteristics of ZnSe epilayers by Metal-Organic Chemical Vapour Deposition (MOCVD) at atmospheric pressure. Gas flow patterns

entrance effects and boundary layers within reactors have been investigated.The experimental techniques employed are TiO

2

smoke trace and it’s photogrammetry. The results are analysed in terms of accepted simplified theories of gas flow dynamics involving a group of dimensionless number-Re

Ra and Gr/Re

2

. The de-pendance of the stagnant layer thickness (δ) on the distance along substrate holder (

x

)

the gas velocity (

U

∞

) and the temperature (

T

) was experimentally observed.It tallys with the Berkman’s typical expression for the boundary layer thickness.The growth rate (

G

) has been studied as a function of distance along (

x

) and across (

z

) the susceptor. It is independent of the temperature between 450-530℃ for Diethylzinc (DEZ)and 280-390℃ for Dimethylzinc (DMZ) respectively. This shows that the deposition is controlled by the diffusion of reactants across the stagnant layer.