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.

PRINCIPLES Oir THE INJECTOR 85 The total heat in 1 Ib. of the steam entering tlie injector above what is contained in the dølivery jet is 1,035 B.T.U. (1,210 — 175). The amount of heat energy actually con- verted into work in the injector we find to be 4’7 B.T.U., so thatthere a.re 1,030 units still to be accounted for. The raising of the temperature of 13 Ibs. of water from 97 deg. Fah. to 175deg. Fah. absorbs 1,014 units, lea ving 16 units* as the amount of heat radiated from the injector. We have here neglected the heat energy equivalent of the kinietic energy of the entering feed water, as this is very small, but in the calculations which follow it is considered. The importaiit point to be noticecl is the very small por- tion of the heat energy supplied to the injector which is effeotively utilised as a propulsive force. The reasons for this can be conjecturecL In the first place some of the heat energy of the steam is abstracted therefrom during expansion within the- steam nozzle by the cold feed water around that nozzle. Secondly, the impact of the steam upon the slowly-moving water will cause violent eddying motion®, which will re-convert some of the kinetic energy of the steam jet into heat energy. Thirdly, there is the friction of the jet upon the wadis of the nozzles through whioh it travels, and also the reluctance of the steam and water to quickly unite with one another. A very small portion only of the total heat energy of the steam is actually lost by radiation; the injector miay be considered as a. perf eet applianæ from a thermal standpoint, for praotiøally the wliole of the heat energy supplied is utilised and returned in the delivery jet. It now remains for us to show how the above calcula- tions, based upon actual tests, øompare with those obtained from a theoretical consideration of the action of the appliance. The pressure of the steam working tlie injector is 95 Ibs. per square inch absolute, and the pressure within the injector 5 Ibs. per square inch absolute. In expanding from 95 Ibs. to 5 Ibs. pressure per square inch absolute It is impossible to give this amount with auy great accuracy, as a tempera- ture reading only | deg. incorrect makes a difference in this figure of practioally 10 degrees.