CHAPTER V.
THE DYNAMICS OF STEAM.
24. The Steam-jet.
(a) CONDITIONS OF FLOW.-With a current of steam or gas, as with any other moving body, velocity can be produced only
A! R E BRID H
by the action of force and the expenditure of energy: the force accelerates the mass, the energy is stored in the current in kinetic form. The conditions of perfect flow, under which all the work done in or upon the steam on account of the drop in pressure is changed into kinetic energy of the for- ward-moving jet, are illustrated in Fig. 44. The apparatus consists of the vessel A, the nozzle B, and the tube D; B has the FIG. 44. Conditions of throat or orifice C, then expands or flares to D. In A the pressure is p₁, in D it is p₂; and in entering and passing through the nozzle, the steam loses pressure and gains velocity. It is assumed that no work is lost in overcoming friction, or through any secondary action in the jet. F
Jet-formation. (b) WORK EXPENDED IN ACCELERATION.-Imagine a section- plane across the vessel at EF: steam passing this plane may be thought of as continually pushed forward by the steam behind it; and the work which it receives-and in steady flow would transmit simply and directly to the steam ahead of it, without change-is, per pound, U₁=144p,v=144p₁(x,u,+w₁). (112)
133
.
