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The Manning formula or Manning's equation is an empirical formula estimating the ... the hydraulic diameter as equivalent pipe diameter. It is the only best and sound ...
is the roughness of the inner surface of the pipe (dimension of length) D is inner pipe diameter; The Swamee–Jain equation is used to solve directly for the Darcy–Weisbach friction factor f for a full-flowing circular pipe. It is an approximation of the implicit Colebrook–White equation. [10]
The hydraulic diameter, D H, is a commonly used term when handling flow in non-circular tubes and channels. Using this term, one can calculate many things in the same way as for a round tube. When the cross-section is uniform along the tube or channel length, it is defined as [1] [2] =, where
, the hydraulic diameter of the pipe (for a pipe of circular section, this equals D; otherwise D H = 4A/P for a pipe of cross-sectional area A and perimeter P) (m); v {\displaystyle \langle v\rangle } , the mean flow velocity , experimentally measured as the volumetric flow rate Q per unit cross-sectional wetted area (m/s);
r = radius of the pipe (for a pipe of circular section, the internal radius of the pipe). v = mean velocity of fluid flowing through the pipe. A = cross sectional area of the pipe. In long pipes, the loss in pressure (assuming the pipe is level) is proportional to the length of pipe involved.
In the case of a non-circular cross-section of a pipe, the same formula can be used to find the entry length with a little modification. A new parameter “hydraulic diameter” relates the flow in non-circular pipe to that of circular pipe flow. This is valid as long as the cross-sectional area shape is not too exaggerated.
[3] The report validated the Gauckler formula and by inference, the Manning formula. Strickler proposed that the Ganguillet-Kutter n-value, used to characterize hydraulic roughness in the Manning formula, could be defined as a function of surface roughness, k S {\displaystyle {k}_{S}} .
where is the density of the fluid, is the average velocity in the pipe, is the friction factor from the Moody chart, is the length of the pipe and is the pipe diameter. The chart plots Darcy–Weisbach friction factor f D {\displaystyle f_{D}} against Reynolds number Re for a variety of relative roughnesses, the ratio of the mean height of ...