280 



HYDRAULICS AND ITS APPLICATIONS 



In either case, the coefficient of contraction is unity, and the coefficient 

 of discharge about "98. 



The following values of the latter coefficient are deduced from experi- 

 ments by Freeman 1 on smooth conical nozzles. 



A form known as the ring nozzle is used to a less extent, and consists 

 of a converging nozzle having a circular orifice, which is fitted with a 

 short annular ring of square section (Fig. 126#). This, with a ring 

 -inch square, gives a stream having a vena coutracta of area about '764 

 times that of the orifice. The value of C v is about *97, the coefficient of 

 discharge being about '74. Since the efficiency of a nozzle depends 

 entirely on the value of its coefficient of velocity C v the ring nozzle would 

 appear to have no advantage over the ordinary smooth nozzle, and in 

 practice, with the same pressure head and size of nozzle, throws a jet to 

 a slightly less height. It has been proposed to use a small re-entrant 

 mouthpiece, so as to form a Borda orifice in connection with this nozzle 



(D 



FIG. 127. 



(Fig. 127fo), and to use this as a standard nozzle to experimentally 

 determine the horse-power of a pumping engine, by measuring the 

 pressure inside a nozzle or series of nozzles supplied by the engine. The 

 coefficient of discharge of such a nozzle as shown in Fig. 1276 is given by 

 Freeman as '582. Since, however, the ordinary type of nozzle shown in 

 Fig. 126 a and b may be relied upon to give discharges which are identical 

 within the limits of practical measurement under given pressure con- 



Appendix, Table D. 



