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.

80 THE STEAM INJECTOR. CHAPTEB, VII. Principles of the Injector. In Chapter I. we briefly outlinecl the general principles of the injector, and in succeeding chapters considered th© constructional details of the apparatus. W© will now examine the working of an injector more in> detail. Let us consider, as an example, a jet of dry saturated steam from a boiler under a pressure of 75 Ibs. per squarø inch. aibsolute issuiiig into a region at a pressure of 3 Ibs. per square inch absolute. From formulæ (vi. and vii.) we obtain the velocity (V) of discharge of the steam, —the dryness fraction—-being unity. 3J4 + ♦> - & x- = 11______ (Formula vii.) To 1015 602-6 = -8424 V - J2~g J (^ + "^ L, - (Formula vi.) = x/61-4 x^778 (307'5 +’898Vl41;6-~84 x 1015) W 3250 ft. per second approximately. Now let us assume that the jet of steam. (moving with a velocity of 3,250 ft. per second) enters a nozzle cooled exter- nally, so that the steam is condensed.* The vater jet produoed will have th© same velocity as the steam jet (i.e., 3,250 ft. per second), but its cross-sectionai area will be very con sidera bly less thian that of the steam jet. * If a steam jet is condensed by external cooling means, a transverse or lateral contraction of the jet takes plaee, but the velocity of the jet is not in any way affeeted.