(a) Taking the mean values of ζ given above for pipes of 1 to 4 ft. diameter we get
| d = 5√ (32ζ/gπ2) 5√ (Q2/i) = 0.2216 5√ (Q2/i) for new pipes = 0.2541 5√ (Q2/i) for incrusted pipes; |
(8)
equations which are interesting as showing that when the value of ζ is doubled the diameter of pipe for a given discharge is only increased by 13%.
(b) A second method is to obtain a rough value of d by assuming ζ = α. This value is
d′ = 5√ (32Q2 / gπ2i) 5√ α = 0.6319 5√ (Q2/i) 5√ α.
Then a very approximate value of ζ is
ζ′ = α (1 + 1/12d′);
and a revised value of d, not sensibly differing from the exact value, is