60 DIRECT-CURRENT DYNAMCS AND MOTORS. 
.". Power loss by eddy currents: 
We = 000027 XK 13.33? x 21,537 + .000068 x 13.337 X 2,400 
= 104 + 29 = 138 watts. 
Cooling surface (Fig. 19): 
S. = (444 — 114)zX 2(25 + 114) = 7560 square inches; 
Total energy loss in armature: 
3,780 + 3,650 + 133 = 7,563 watts; 
.’. Specific cooling surface, by (33): : 
s = 7,560 + 7,563 = 1.0 square inch per watt. 
The average rise of temperature corresponding to s = 1, 
from Table 21, is 373° C. 
Circumferential current density, by (34): 
 , CORA BRE = 
= 6.283 XM KO 394 amperes per square inch. 
Average temperature increase corresponding to c = 394, 
from Table 22, for high-speed dynamo, 50° C. 
Mean of the two averages: 3(374 + 50) = 44° C. 
The actual rise of the temperature in this armature, which is 
that of an existing machine, is about 45° C, 
