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.

24 THE STEAM JNJECTOR. Application of Formula (xv.).—To calculate the quan- tity of steam discharged per second into the atmosphere from a boiler under an absolute pressure of 100 Ibs. per square incli through an orifice of 2 square inches cross- sectional area. As the exhaust or counter-pressure is less than "58 of the boiler pressar©, there will be a maximum weight flow through the orifice. 100 x 2 70 = 2’86 pounds per second. By the aid of formulæ (xiv.) and (xv.), the area of an orifice for discharging a known quantity of steam in a given time can be calculated. If the condition for maximum weight flow does not exist, then to calculate the weight of steam discharged in a given time, the following approximate formula must be used: — A x V V2 (xvi.) where W denotes weight in pounds of steam discharged per second, A area of orifice or of nozzle throat in square feet, V the velocity of the steam in feet per second as it passes the nozzle throat, and v2 the volume in cubic feet of 1 Ib. of steam at the pressure in the exhaust space or space into whicli the steam is flowing.* The dryness fraction is negle ctecl. Application of Formula, (xvi.).—To calculate the weight of steam discharged per seconcl through an orifice of l square- foot cross-sectional arr a, when the initial pressure is 100 Ibs. per square inch absolute, and the final or exhaust pressure is 80 Ibs. per square incli absolute. We first calcu- late the velocity of discharge. Using formula (xi.), we get V = 279 J 100 x 4-33 = 944 ft. per second ; The value v2 should be multiplied by the dryness fraction for æreater accuracy.