Key words: Boundary layer, laminar flow, heat transfer, Richardson number, diffusion, friction coefficient.

Abstract: The laminar boundary layer is frequently found in nature and in industry. For example: aerodynamic, hydrodynamic, in meteorology and in oceanography. Such as: it causes many problems in aerodynamic such as a jet engine. A numerical study of the boundary layer developing along a horizontal plate is carried out . The aim of this work is to study the effect of Richardson number on thermal and mass behavior of laminar boundary layer, when the flow is subjected to thermal and solutal diffusions.