Boundary-Layer Concept. Laminar Forced Convection

1 BOUNDARY-LAYER CONCEPT. LAMINAR FORCED CONVECTION O 

In Chapters 2 and 3 we have already introduced the concept of penetration depth for an approximate solution of conduction problems (recall Section 2.4.1, and Exs. 2.11 and 3.9). This concept, which we utilized to determine the steady or unsteady penetration depth of heat (or thermal boundary layer) in solids and stagnant fluids, actually applies to all diffusion processes, such as diffusion of momentum, mass, electricity, and neutrons, as well as diffusion (or conduction) of heat It is a convenient tool for an approximate solution of conduction problems and is indispensable for convection problems, which are considerably more complicated than conduction problems. 

For example, in terms of a parabolic profile approximating the temperature distribution in an infinite fin, we obtained in Section 2.4.1 

Clearly, except for a numerical constant depending on the assumed approximate profiles, Eqs. (2.125) and (5.10) for the penetration depths are identical. 

Separately, on dimensional grounds, we have from the first law applied to a system of 8 extent (Fig. 5.4), 

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Sec. 5.1 Boundary-Layer Concept. Laminar Forced Convection O 245... 

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