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 DELIVERY NOZZLE. 41 velocity and density of the water as it passes the throat; that is, a“vVd.........................(xxvL) where A = area in square feet, Q = quantity of delivery water in pounds per second, V = velocity of water in feet per second, and 1) = density of water in pounds per cubic foot at the delivery temperature. The actual weight of water passing through the delivery nozzle is, of course, made up by the total weights of steam and water entering the injector. The water velocity at the delivery nozzle throat may for the purpose of the above calculation be taken as 25 per cent greater than that with whicli a jet would issue from the boiler being fed. From the foregoing the following general conclusions may be drawn as to the design of a delive-ry nozzle: — (2) The nozzle should not be too short, or the quick change of cross-sectional area required to obtain the neces- sary reduction in the velocity of the jet will set up eddying motions, and so impair the power of the jet. In other words, there should not be a vei'y abrupt rise in the pressure curve. (3) The form of nozzle should provide for a fairly regular rate of conversion of velocity into pressure so as to produce stability in the jet. In other words, the pressure curve should not have any clecided humps upon it. (4) The nozzle surface should be as sniooth as possible, so as not to produce eddying motions in the jet, and to offer a minimum of resistance to its flow. Table IV. gives the approximate cleliveries of different sizes of live steam injector when fitted non-lifting, with the feed water temperature about 60 deg. Fah. An increase in the said temperature, as also the fixing of an injector above the level of the feed water, causes a diminu- tion in the delivery.