The first part of the paper concerns the cases where in spite of the stationary boundary conditions the flow becomes non-stationary due to the substantial inhomogeneity of the moisture production process.

The results of experimental investigations carried out with the use of high-speed film and pressure sensors of small inertia have been presented. It was shown that in the conditions of spontaneous condensation in transonic regions non-stationary periodical shock waves are generated. This results in significant pulsations of parameters, with frequency bętween 300 and 1000 Hz. 

A theory of transient flow of compressible medium with phase changes was developed. Result calculations of such a flow in channels of various geometry, made with the aid of a B3CM-6 computer have been presented. Sets of nonlinear differential equations were solved by means of the grid method.