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. 9 obvious that it is not acting in the most efficient manner, for to fulfil the latter condition all the energy imparted to the feed water should be in a direction parallel with the axis of the steam nozzle. It will b& understood that for maximum efficiency, eddy motion in the steam jet should be a minimum. In 1869 it was proposed to make the injector steam inlet nozzle diverge towards its mouth or exit, so that the steam would expand within the nozzle down to the pressure of the medium into which it is flowing. The jet issuing from the nozzle is then of cylindrical form. The expansion of the steam within the limits of the nozzle ensures that the jet shall have maximum velocity as it leaves the same (for the lower the steam pressure at the nozzle mouth with a given initial pressure the greater the velocity of discharge), and also that eddies in the jet shall be reduced to a minimum. Fig. 5 shows an injector steam inlet nozzle with a diverg- ing mouth piece, and a steam jet issuing therefrom. In live steam injectors, the angle of divergence of the steam nozzle is generally between 5 deg. and 15deg. If the angle of divergence be too great, eddies form in the jet and produce loss in velocity, whilst if it be too small the nozzle has to be of excessive length to provide for a proper degree of expansion of the steam issuing there- through. Eddies commence to form in the steam jet if the angle of divergence exceeds 6 deg. In Rosenliain’s experi- ments* to determine the most efficient form of nozzle for developing the greatest kinetic energy pei’ poimd of steam * Proc. Inst. C.E., vol. cxl., page 199.