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XXV. Fluid Discharges as affected by Resistance to Flow. 

 By Wm. John Walker, B.Sc, Ph.D., Lecturer in 

 Engineering, College of Technology, Manchester*. 



TYPICAL instances of fluid discbarges, greater than 

 appear to be possible from theoretical considerations 

 of non-viscous flow, are those of the Venturi meter for low 

 heads, and also, under certain conditions, the discharge of 

 steam through nozzles. The latter case is explained by 

 H. W. Oallendar's " supercooling theory " f . The following 

 analysis shows, however, that the discharge of a viscous 

 fluid may actually be greater, under otherwise similar con- 

 ditions, than that of a non-viscous one. This result appears 

 to be paradoxical in the extreme, and it is with the greatest 

 diffidence that the writer advances it here. His excuse lies 

 in the fact that the deduction is the result of the inclusion 

 of a resistance expression which holds in certain cases of 

 fluid motion. 



The Venturi meter, used principally in water-flow measure- 

 ment, consists essentially of a converging circular tube, the 

 pressures at the entrance and exit of which are measured, 

 the difference between these serving as the measure of dis- 

 charge. The theoretical formula for non-viscous flow is 



, area at entrance 



where m— : -. — , 



area at exit 



v — velocity of fluid in feet per second, 



and h = pressure difference in feet of water. 



In practice this is written 



where C is known as the " meter coefficient." Naturally 

 this is less than unity, having values from '96 to '99. At 

 low velocities, however, values as high as 1*36 J and as low 



* Communicated by the Author. 



\ " On the Steady Flow of Steam through a Nozzle or Throttle," 

 Proc. I. M. E. p. 53 et seq., Jan. 1915. 



X Coker, Canadian Soc. C.E. March 1902. See also Gibson, Proc. 

 I. C.E. p. 392. 



