The equations governing the flow of a fluid and the associated heat transfer are based on the conservation principles for mass, momentum, and energy. These equations are first presented for a compressible, viscous, Newtonian fluid, and then particularized for simpler cases. It is assumed that the reader has some background in this field. Thus, a complete derivation of the gov­ erning equations is not included. The reader is referred to Schlichting (1979) for the derivation. For the general case of three-dimensional motion, the flow field is specified by the velocity vector

V = ui + vj + wk

where u, v, w are the three orthogonal components, by the pressure p, density p, and temperature T, all conceived as functions of the space coor­ dinates and time t. For the determination of these six quantities, there exist six equations: the continuity equation (conservation of mass), the three equations of motion (conservation of momentum), the energy equation (conservation of energy), and the thermodynamic equation of state p = p(p, T).