373
OF ENGINEERING FOBMULÆ.
Ventilation of Tunnels—continued.
(D. K. Clark, ‘ Min, Inst. Civ. Eng.,’ vul. xliv.)
Ä = Head of pressure in inches of water.
= 5'20 lbs. per square foot per inch.
V = Velocity of current in feet per second.
P — Perimeter of tunnel in feet.
A = Sectional area of tunnel in square feet.
HP = Horse-power.
L = Length of tunnel in feet.
x V2PL „„ V3P1? VAI ,
Å . HP = ------------- — -------; for
633000 A 67,000,000 106
„ V3PL
lation with brattices, HP = -___„ ■ •
10,000,000
Radiation of Heat.
(Anderson, ‘ Min. Inst. Civ. Eng.,’ vol. xlviii.)
T — Temperature of air surrounding pipes.
t = Difference of temperature of air and that of pipes.
m = Coefficient of radiation.
u = Total units emitted per square foot by radiation and
convection.
U = m X l-00427T(1-00427' — 1) + -2853 X J1-233.
U - 0-2853 X t1’233
m = --------—---------------•
1 -00427t (1 • 00427‘ — 1)
(1) m = 270'9 for a single coil of 2-in. galvanized pipe.
(2) =252-9 for the same, with a vertical sheet of Iron
between the coils.
(3) = 211-0 The same as No. 1, blackleaded.
(4) = 235 • 3 The same as No. 2, blackleaded.
(5) =231‘8 The same as No. 1, with a similar coil.
(6) = 121 • 7 for a coil of 4-in. cast-iron pipes.
(7) -123-0 Coil of 2-in. cast-iron pipe, blackleaded.
(8) = 108*8 Same as No. 7.
(9) — 272’3 2-in. wrought-iron tubes connecting two cast-
iron steam-chests.
* Actual; 2} times this horse-power should be provided.