Comments on Location of Detached Shock Waves Ahead of Plane Bodies

(12) These properties are exactly those of an ideal gas. Define further a quantity a corresponding to the entropy by da = ds/z(s). If now Eqs. (10) and (11) are substituted into Tds = dh — vdp, one obtains da = \R(dr/r) - R(dp/p) Because of Eq. (12), a is separable as in case of the entropy of an ideal gas. In fact, a medium defined by Eq. (3) has all the mathematical properties of an ideal gas as discussed in reference 1, Section 4, if T is substituted by r, s by a, cp/R by X, cv/R by X — 1, and K by k. It seems, therefore, appropriate to call it an ideal vapor or a perfect vapor, following Leib.4 If, in addition, Eq. (4) is true, then the medium can in most cases be treated as a polytropic gas and may be called a polytropic vapor. In this case, Eq. (10) can be integrated explicitly to give h = \pv, corresponding to h = cpT for a polytropic gas. The integration constant has been set equal to zero. Traupel2 mentions that the equivalence breaks down if heat conduction is present. This situation can be saved sometimes, at least formally, if the gradients of T and of h can be considered as parallel. It is then possible to define an enthalpy difrusivity which relates the heat flux to grad. h as the thermal conductivity is related to grad. T. This diffusivity, unlike the conductivity, is, however, not a unique function of state unless the state path