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.

NOZZLE DIMENSIONS. 95 Proceecling from the test figures given, we obtain the qiiantity of water delivered per pound of steam, the formula for which is as follows: — TTTT ti X1 Li “* tn / • • • \ W = 1 11 8 . . . (xxvin.) - t., ' The velocity of the incoming feed water is found by taking into account the actuail head of water (whether posi- tive, zero, or negative) and the head due to the difference between atmospheric pressure and the pressure within the injeotor. With the above results we obtain the theoretical velocity at the delivery nozzle throat. We tlien proceed upon the following lines: — Since from our experimental results we find that 1 Ib. of steam delivered B pounds of water to the boiler, C then to feed C pounds of water per second will require — B pounds of steam per second. The specific volume v of the ateam at the steam nozzle throat is— v = x., u., + (1 — a?2) er . . . (xxxiii.) w x2 u2 approximately . . , (xxxiv.) where x.> = the steam dryness fraction at the nozzle throat, u2 = the specific volume of 1 Ib. of steam at the pressure at the throat, and o- is the specific volume of 1 Ib. of water. Fro ni the above the throat area of the steam nozzle is given as follows :— x C (,, ,, + (1-^)T) _ . B x V, where Vt = the velocity of the steam at the nozzle throat, which is readily obtainable from the maximum velocity, equation (xvii.) as follows :— V throat = /2 g x 144 vx. J n + 1 711 This value is uaually about 1,500 ft. per second, and need not be specially calculated for approximate results.