∴ d = αv2/gi + √ {(αv2/gi) (αv2/gi + 1/6)}.
(6)
For practical purposes, the approximate equations
| d = 2αv2/gi + 1/12 = 0.00031 v2/i + .083 for new pipes = 0.00062 v2/i + .083 for incrusted pipes |
(6a)
are sufficiently accurate.
Problem 5. Given the virtual slope and the discharge, to find the diameter of the pipe and velocity of flow. This case, which often occurs in designing, is the one which is least easy of direct solution. From equations (2) and (3) we get—
d5 = 32ζQ2 / gπ2i.
(7)
If now the value of ζ in (1) is introduced, the equation becomes very cumbrous. Various approximate methods of meeting the difficulty may be used.