Enthalpy thickness

A quantity defined by the identity

where h, h₁, h_w are the current value of the enthalpy and its values in the external flow and at the wall in a given cross section of the boundary layer. Remaining symbols as in displacement thickness.
Comment. If the quantities h and h₁ are taken as the corresponding stagnation enthalpies, the quantity defined by this identity is called the "stagnation enthalpy loss thickness" (Δ₀**).