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.

88 THE STEAM INJECTOR. Generally speaking, the most efficient injector is one whiøh, when delivering- i nto a boiler under a certain pres- sure, passes the greatest ratio by weight of water to steam. If, hcwever, we are oonsidering an injector from the point of view of the temperature of the feed water it can deal witih when the steam is at a certain pressure, the most efficiient injector is one capa/ble of taking the hottest feed water with the steam at thait pressure. If the nunaber of heat units contained in 1 Ib. of the steam entering the injector be known, also the temperatures of the feed or supply water and of the delivery jet, then with tx + Lj denoting the total heat contained in 1 Ib. of the ,steam, ti the temperature of the feed water, t3 the temperature of the delivery, and W the weight in Ibs. of water per Ib. of steam, Gain of heat by feed water = W (^3 - t.,). Loss of heat of 1 Ib. of steam = t1 + lx - t3. Heat equivalent of the kinetic energy of the jet leaving the injector = (W + 1) x V3 2 <7 x 778 where V — velocity of delivery jet in feet per second. If the extre-mely small amount of heat energy repie- sentied by the kinetic energy of the entering feed water be neglected, also the loss of heat due to radiation from the injector, then :— Loss of heat Heat equivalent of kinetic . , „ , by steam = energy of delivery jet + fee<i We have already seen that the heat equivalent of the kinetic energy of the delivery jet is very small, and it can be safely neglected without materially affecting the results. The equation then becomes:-—- tx + Lx - t3 = W (t3 - i.e., AV = .... (xxviii.)