| Fig. 213. |
Taking some of Messrs Heenan and Gilbert’s results for ordinary fans in normal conditions, they have been found to agree fairly with the following approximate rules. Let pc be the compression pressure and q the volume discharged per second per square foot of outlet area of fan. Then the total gauge pressure due to pressure of compression and velocity of discharge is approximately: p = pc + 0.0004q2 in. of water, so that if pc is given, p can be found approximately. The pressure p depends on the circumferential speed v of the fan disk—
| p = 0.00025 v2 in. of water v = 63 √p ft. per sec. |
The discharge per square foot of outlet of fan is—
q = 15 to 18 √p cub. ft. per sec.
The total discharge is
Q = π dt q = 47 to 56 dt √p
For
t = .35d, d = 0.22 to 0.25 √(Q / √p) ft.
t = .45d, d = 0.20 to 0.22 √(Q / √p) ft.
N = 1203 √ p/d.