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.

28 THE STEAM INJECTOR. CHAPTER III . The Combining Nozzle. Tue nozzle into which the steam and water issue after they have entered the injector is called the combining or mixing nozzle, foi’ in it the steam and water combine or mix, with the result that the steam. is condensed and a water jet alone pases through the nozzle exit. It is impossible to treat of the combining nozzle with anything like mathematical pre- cision, for there are so many different quantities to be con- sidered in relation thereto, and none of them. has a fixed value. In the design of this nozzle, particular regard must be given to the following considerations : — (1) The length of the nozzle must be such as to ensure the complete condensation of the steam jet, so that water alone passes through the nozzle exit. (6) Its walls must converge at a rate corresponding with the rate of increase of density of the jet passing through the nozzle; that is to say, the jet must fill, and only fill, the nozzle at all points in its length. (c) The inlet end of the nozzle must provide a guiding and supporting wall for the water as it enters the injector, and during the impact of the steam thereon. (The question of the overflow and water Control arrange- ments of the combining nozzle are dealt with in Chapters IV. and V.) In the consideration of the above points, the following should be borne in mind. In the first place, the volume of 1 Ib. of steam varies with the pressure of the steam, as does also the temperature. Secondly, the rate at which steam of a certain temperature can be condensed depends upon the temperature of the water by which condensation is being effected. Thus it would appear that a special length and shape of nozzle is necessary to suit different steam pressures and temperatures, and also different feed-