Envco – Environmental Equipment

One side determines the flow of water through pipes and ducts of circular cross section and constructed in a variety of materials, i.e., metal pipes, concrete ducts. coated pipes etc. The other side deals with the flow in large open channels of any cross section, rectangular, round, etc.

Pipes, Ducts & Sewers
This side of the calculator solves the rational formula for the flow of fluids in pipes, incorporating coefficients of friction in accordance with the Colebrook-White equation and pipe roughness factors.

The rational formula as applied to water flow is
P = 3.25 x 107 Q2 f L / D5

where:-
P = pressure loss bar
D = bore of pipe, mm.
Q = flow, litre/s
f = coefficient of friction

L = length of pipe, m.

The Colebrook-White equation is :-

1 / Öf = - 4 log (Ks/3.7d + 1.255/RÖf)

where:-
Ks = absolute roughness of pipe in mm. (This approximates to the dimensions of the particles or granularity of the material causing roughness.)
R = Reynolds Number. (A dimensionless number related to viscosity and the boundary layer).

The variable coefficient of friction is built into the calculator and needs no separate determination and a Pipe Material scale makes appropriate allowances for roughness.

The Rational formula combined with the Colebrook-White equation for the coefficient of friction on which this model is based takes account of pipe roughness, viscosity, and Reynolds Number and has been practically universally adopted as the most logical and accurate for problems of fluid flow in pipelines. The answers have been checked against over 100 well authenticated practical tests on actual pipelines from small metal tubes to long concrete tunnels up to 6 m dia., and give an accuracy appreciably better than the usual Hazen-Williams formula. The pressure loss obtained is for pipes in new condition and allowance should be made for deterioration with age due to corrosion or incrustation according to experience with the type of water being handled. This will result in an increased pressure loss or a reduction in the flow.

Scales are provided, coloured green, for determination of velocity.

Flow in Ducts Running Partly Full
The flow through any pipe, duct or open channel running only partly full can be read off directly against the Proportional Depth scale on the top quadrant. Thus if the depth of water in the pipe is only one quarter of the diameter, the flow is read off immediately opposite .25 on this scale.

It will be seen that paradoxically there is a slight increase in the flow with a pipe only say 95% full, this being due to the appreciable reduction in the length of the wetted perimeter causing a corresponding reduction in the frictional losses as the water leaves the top of the pipe.

With partly full pipes the flow is determined by the slope. Thus if the slope is 1 in 600 it will be appreciated that there is a loss of pressure head of 1m in every 600m of length. To determine the flow therefore the pressure loss is set at 1m and the length at 600m

Open Channels
To deal with open channels of non-circular section the other side of the calculator is arranged to solve the Manning Formula which is:

Q = A1.66 S0.5 / n P.66
where:
Q = flow in m3/s
A = area of channel in m2
n = Kutters 'n'
P = wetted perimeter of channel in metres.
S = slope of channel
It is necessary to obtain the area of the channel occupied by the water and also the corresponding length of the wetted perimeter and to use these values in the calculation.

The Manning Formula will also deal with the flow in circular channels running partly full but it will give low values for the smaller pipes and steeper slopes and it is preferable to use the other side of the calculator

Ordering Information
34259 Water Flow Calculator