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. 23 The above results have been verified by experiment. It is found in the case of the flow of dry saturated steam through a nozzle that if the initial pressure (/>1) of the steam be maintained constant whilst the counter-pressure (ja) is varied, the weight of steam discharged in a given time remains practically constant until the counter-pressure rises to 0’58 of the initial pressure. There is always a certain section of the steam nozzle at or about its throat at which the steam pressure remains at 0’58 of the initial or boiler pressure until the counter-pressure exceeds this amount. If reference be made to ligs. 4 and 6, it will be søen how reluctant the pressure at the nozzle throat is to be influenced by varying counter-pressures. If the valnes of — given in equation (xiii.) be substitnted in equation (xii.), the weight of steam discharged per second, under conditions of maximum weight flow, is given as follows : — W = V (~T~i?2y x —- x 144^^ vL ' n + 1' v n + 1 = A (—7—?)'<■ i / 2 <j x —-— x I 44 x P-2 . (xiv.) V 7 J n 4. 1 *>1 where AV denotes pounds of steam discharged per second, A area of nozzle throat in square feet, n the co-efficient of expansion, pi the initial or boiler pressure in pounds per square inch absolute, and v2 the volume in cubic feet of 1 Ib. of steam at pressure pL. A simple approximat© formula for obtaining the weight of steam discharged per second through an orifice under maximum weight flow conditions is: — W - 11^2 (Napier)* .... (xv.) where W = weight of steam discharged in pounds per second, p = absolute pressure of boiler steam in pounds per square inch, and A = area of nozzle throat in square inch.es. * A more correct approximation is W = -01654 A x p*»»»®.