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. 37 the initial pressure as zero. The diameters of the nozzle at the different equidistant sections are as follows : — Section 1 ................ Diameter 1 or unity. „ 2 ................. „ 1-034. ................. „ 3 ................. „ 1-074. „ 4 .........................., 1-124, „ 5 ................. „ 1-188. „ 6 ................. „ 1-276. „ ‘ ................ „ 1-411................ „ 8 ................. „ 1-673. „ 9 ................. „ 4-152. It will be seen that the rate of increase in the diameter of the nozzle is very slow right up to section 8. It is found in practice that if the jet contain any solid matter, abrasion of the deliveiy nozzle takes place chiefiy around the throat or first portion of the latter. It is usual practice to make the d&livery nozzle of cylindrical form at the throat for a length equal to the diameter of the throat, as shown at fig. 19. If the form of the nozzle be such as to cause a very sudden increase in the pressure of the jet at a point near to the throat of the nozzle where the velocity is high, the jet sets up a strong abrading action on, and tends to groove, the nozzle surface at that point. In this respect the form of nozzle shown at fig. 18 is better than that shown at fig. 17. Towards the delivery end of the nozzle the velocity of the jet is small, and wear is reduced to a minimum. In most injectors the delivery nozzle has a plain, conical throughway aperture, as this form of nozzl& lends itself to economical manufacture. A nozzle of this type is illus- trat&d at fig. 20, which also gives corresponding velocity and pressure curves when the entering velocity is taken as 200 ft. and also as 100 ft. per s&cond. It will be seen that with this type of nozzle there is at first a rapid rise and then a slow rise of pressure which will result in the prcduc- tion of eddying motions in the jet between the sections 1