THEOKY OF TURBINE DESIGN 555 



to be p% Ibs, per square foot, the total unbalanced pressure over this 

 portion, in the direction of the suction tube is equal to 



^rP [ ( SJ - S >< H + P5? - H + Pff >< ) 



x 3,0,0 + x 6>040 



= '7854 { 752 + 2,105 + 3,680 + 6,960 + 13,210 } 

 = 21,000 Ibs. 



AKT. 146. THE OUTWARD RADIAL FLOW PRESSURE TURBINE. 



The general details of design of the outward flow turbine are 

 exactly the same as for the inward flow type, and the same symbols and 

 equations apply throughout. 



Now, however, n = -is less than unity, so that in equation (16), 

 **a 



p. 539, 



/ 3 2 co8ec 2 y-/ 2 2 cosec 2 /3 



_-i , 



W ~2g\ n*J ~ 



the term jp- M --- ^ ) is negative, while, strictly speaking, the second 



term of the equation ceases to apply, since the flow now takes place 

 through a series of diverging channels, and eddy formation is in con- 

 sequence set up. 



Centrifugal force now aids the flow through the turbine, and an 



2 ( - I \ 

 increase in speed, by increasing the term _ \ w 2 _ / , decreases the 



29 



inlet pressure, and causes an increased flow through the wheel. This 

 turbine is in consequence difficult to govern satisfactorily. To reduce 



this effect as far as possible the term ^ lJ should be small. This 

 necessitates n or being made as nearly unity as practicable, and 



r 3 



necessitates a bucket depth as small as is compatible with easy curves 

 connecting inlet and outlet lips. In general 7*3 is made from 1'20 to 

 1*25 times r 2 . 



Owing to the high peripheral velocity at exit, it is now impractic- 

 able to design the exit angles so as to make the velocity of whirl at exit 

 equal to zero. The losses due to rejection of kinetic energy are thus in 

 general higher with this than with the inward flow type. 



