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.

92 THE STEAM INJECTOR. is feeding a boiler at the same pressure as the steam enter- ing the injeotor, to increa.se the ratio of steam to water above that wliicli gives maximum delivery pressure and temperature-, whilst obtaining a perfect action of the appha.noe. The rate of supply of water to the boiler can theretfore be varied wit-hin fairly wide limits to sult requirements. We have already seen liow vei’y small a portion of the heat energ-y of the steam entering an injector is actually utilised by conversion into kinetic energy in the propulsion of the water jet through the applianoe. It follows, tliere- fore, that a jet apparatus is very inefficient merely for pumping purposes. The actual efticiency of the apparatus- is represented by the ratio of the work done by the steam jet to the amount of heat yielcled by the steam to perform that work ; i.e. : where E = mechanical efficiency, U — work done by steam, ty = sensible heat of steam, Li = latent heat of steam, and t3 = heat units in 1 Ib. ot delivery jet. Now, U is represenrted by the mechanical work performed by the steam in giving the water jet a certain pressure or in delivering it to a certain height—the equivalent of said pressure—and also in raising the water to the jet pump, if the latter is fitted above the water supplv. That is IT — x Z + (W + 1) hp\ , . A (------------1--------—L- J in heat unita, where AV = ratio in pounds of water to steam passing through the apparatus, l — suctiou lift in feet, = head equivalent of delivery’pressure, B delivery pressure in pounds per sq. inch x 2'3. J = Jonle’s equivalent = 778 foot-pounds per B.T.U.