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.

THE STEAM NOZZLE. 25 v2 = 5’35 (from “Steam Tables”); • w _ 1 x 944 öW — 176'4 Ibs. per second.' If the valne of given in equation (xiii.), be substituted in equation (x), the velocity of the steam at the nozzle throat under maximum weight flow conditions is obtained as foliows : — Vthroat ~ J 2 9 x । x 1^4 x • (xvii.) It is perhaps hardly necessary to point out that whilst the velocity of the steam at the nozzle throat does not vary with variations in the pressure at the nozzle exit until the condition for maximum weight flow ceases to exist, the velocity of the steam at the nozzle exit varies with every variation in the pressure at the said exit, as will be reaclily appreciated from the velocity formulæ already given. Design of Steam Nozzles. To determine theoretically the relationship between the areas of nozzle throat and mouth for correct expansion from any one pressure to a lower pressure, the conditions of the steam jet as to velocity, density, and dryness at the said points should be compared. If A denotes area, V velocity, v volume, the suffixes vi and t nozzle mouth and throat respectively, and x the dryness fraction of the steam, then the following will be an approximate formula for calculating the said ratio of areas: — Am = x l’m x X'n vi xt (xviii.) Application of Formula (xviii.).——To calculate tlie ratio of areas of the throat and mouth of a diverging nozzle in order to expand dry saturatecl steam of 100 Ibs. pressure per square inch absolute down to 1 Ib. absolute pressure.