The skin-friction thermal factor and the recovery factor from continuum flow to free molecule flow

A thermal factor and a recovery factor were introduced into an analysis of forced convection's skin friction temperature, and their changes were analyzed as dependent on the main parameters that control the forced convection. In the case of a continuum flow, it is shown that the skin friction thermal factor's limiting value for high Mach numbers is 0.94, in keeping with the recovery factor based on skin friction temperature. The fact that the skin friction thermal factor is a flow invariant in a free molecular stream, independent of Mach number, has permitted the determination of a uniform dependence for the skin friction thermal factor in continuum-to-free molecule flow transitions by introducing a normalized thermal factor that is a function of the Knudsen number.