General comments on the solution of boundary layer equations

4 General comments on the solution of boundary layer equations 

The equations (3.109), (3.117) or (3.118) and (3.120) for the velocity, thermal and concentration boundary layers show some noticeable similarities. On the left hand side they contain convective terms , which describe the momentum, heat or mass exchange by convection, whilst on the right hand side a diffusive term for the momentum, heat and mass exchange exists. In addition to this the energy equation for multicomponent mixtures (3.118) and the component continuity equation (3.25) also contain terms for the influence of chemical reactions. The remaining expressions for pressure drop in the momentum equation and mass transport in the energy equation for multicomponent mixtures cannot be compared with each other because they describe two completely different physical phenomena. 

The equations are the basis for many technical applications. However, before we investigate particular solutions, it would be sensible to make some general remarks on the solution of these equations. 

To this effect, the equations will once again be brought into a dimensionless form. As we are only interested in discussing the characteristic features of the solution, and not as in the derivation of the boundary layer equations, where an estimation of the magnitude of the individual terms in a particular equation was required, all the quantities in the equations will be made dimensionless in the 

Chemical reactions will not play any role in this discussion. The considerations here will be restricted to pure substances or binary mixtures which have components of approximately the same specific heat capacity. The energy equation (3.119) then agrees with that for pure substances (3.117). After introduction of the dimensionless quantities the continuity equation is 

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