The Steam Injector
A theoretical and practical treatise on the design and operation of injectors and on the flow of fluids through and the design of nozzles.

THE STEAM NOZZLE. 7 CHAPTER II . The Steam Nozzle. As the kinetic energy of steam is the force utilised in an injector for propelling the feed vater into the boiler or vessel being fed, it is necessary that the injector steam inlet nozzle be so designed as to develop under any given conditions tlie greatest kinetic energy per pound of steam discharged therefrom. In the days of the early injectors the properties of steam were not thoroughly understood; engineers treated steam in the same manner as they would trcat water or other inelastic fluid. To obtain the maximum velocity of dis- charge of water from a nozzle, the- latter is made of con- vergent form; so in the early injectors a converging steam Fig. 3. inlet nozzle was employed. In tlie Giffard injector illus- trated at fig. 1 there is a converging steam inlet nozzle a. With this form of steam nozzle, as with. a straight or cylindrical nozzle, the issuing steam is of greater pressure than the medium into which it flows, and expands laterally immediately it leaves the nozzle. Fig. 3 shows a convei'ging steam nozzle with a live steam jet issuing therefrom.* Fig. 4 shows in diagram form tlie fali of pressure in a steam jet issuing from a plain tube, such as indicated at * This figure must be taken as approximate only, as the exact form of the jet depends on conditions which vary with every nozzle. See Rosenhain’s paper referred to on page 9.