214 



HYDRAULICS AND ITS APPLICATIONS 



Other experiments have been carried out by Cole 1 and by Morrow, 2 

 from whieh, together with those already quoted, it may be concluded that 

 in gaugi rig the discharge of a pipe by means of a Pitot tube (p. 218), the 

 mean <jf observations at a radius varying from '69 a in small, to "75 a in 

 largo pipes, will give the mean velocity directly, while the mean of 



observations at the 

 centre of the pipe 

 when multiplied by a 

 constant varying from 

 79 to -86, with an 

 average value of '84, 

 will also give the 

 mean velocity with a 

 fair degree of accuracy. 

 Experiments by R. 

 Threlfall, 3 on the flow 

 of air through gas 

 pipes from 6 to 36 

 inches diameter, in- 

 dicate that here the 

 radius of the circle of 

 mean velocity is about 

 G'775 of the pipe 

 radius, though in one 

 case of a gas main, 

 15f inches diameter, 

 the radius of mean 

 velocity was about *9 



.tf* 



4-93\Cms. Velocity at Axis* 

 7-40 Cms. Velocity at A*is*IO 17 Cms.perSec 



2 -3 -4 -5 -6 7 -8 -9 

 Radius m terms of outside radius of Pipe, 



R. 



FIG. 98. 



of the pipe radius. 



The ratio of mean 

 to maximum velocity 



in these experiments was very constant over a wide range of velocities 

 22 /.a to 41 f.s. and had the mean value 0'873. 



Eecent experiments by Michael Longridge 4 on air flow through a 

 16-inch pipe at velocities ranging from 77 to 210 feet per second showed 

 that the ratio of mean to maximum velocity varied by less than 1J per 



1 " Trans. Am. Soc. C. E.," 1902, vol. 47, pp. 63 27G. 



2 Proc. Roy. Soc.," 1905, vol. 76, p. 205. 



3 " Proceedings Institute Mechanical Engineers," 1904. 



* " Engineer's Report of Brit. Engine and Boiler Insurance Co., Ltd., for 1910," p. 92. 



