DIRECT-CURRENT DYNAMOS AND MOTORS. 57 
The flux density, B,, in the armature, is the flux divided 
by the armature cross-section. The flux in the present 
case is: : 
_ 6 X 10° X 1 X 125 
336 X 1800 
and the cross-section of the armature: 
2B, Xx .9L, = 1.8 X 1$ X 94 = 31 square inches. 
Hence we have: 
B,= —_— = 40,000 lines per square inch; 
and, the hysteresis factor, from Table 19, n = .0067. 
From (29) we therefore obtain the power absorhed by 
hysteresis: | 
Wy, = .0067 xX 30 X 190 = 38 watts. 
The eddy current factor for a flux density of 40,000 lines 
per square inch, if the sheet iron used is .020 inch thick, 
is € = .000027, according to Table 20, consequently the 
power absorbed by eddy currents, from (32): 
w. = .000027 x 30° x 190 = 5 watts. 
The approximate cooling surface of the armature, from (7), 
is: 
d 
= 1,240,000 lines, see (21), 
S, =5% x X 9F + (53)? : = 167 + 26 = 193 sq. in. 
Dividing S, by the total power loss in the armature, the 
specific cooling surface is obtained, see (33): 
_ 193 7 
24+ 38+5 
The average temperature increase corresponding to this 
value, according to Table 21, is about 40° C. 
By formula (34) the circumferential current density of the 
given armature is: 
¢ — __336 x 42 
~ 6.2838 x 5$ x 1 
Ss 
.75 square inch per watt. 
= 390 amperes per inch. 
