|
CALCULATING FLOWS
Pressure drop due to friction can be determined for practical use purposes using the flow nomogram. The nomogran is based on the Colebrook White formula for water at 10°C using a hydraulic roughness factor K of 0.003mm.
The pressure drop at a given flow rate can be determined as follows:
1. Obtain the internal bore diameter of the pipe to be used by referring to the dimensions tables.
2. Mark this diameter on Scale A.
3. Mark the required flow rate on Scale B.
4. Draw a straight line connecting the points on Scales A and B and extend the line to cross Scales C and D.
5. The velocity of flow in metres per second is determined from the intersection with Scale C.
6. The frictional head loss in metres per 100 metres of pipe can then be read off Scale D.
Fittings
The calculation of pressure drop in fittings is more complex, but calculations can be made for equivalent lengths of straight pipe using the formula E=F¥D where:
E = is the equivalent pipe length (metres)
F = is the fittings constant (See below)
D = is the fitting internal diameter
To calculate the total pressure drop in the system, the equivalent straight pipe lenghts for fittings is then added to the total straight pipe length to obtain the total drop.
Fittings Constant
|
FITTING |
F |
|
90° Elbow |
0.030 |
|
45° Elbow |
0.015 |
|
90° Tee - Straight Through |
0.020 |
|
90° Tee - Side Branch |
0.075 |
|
90° Long Radius Bend (4D) |
0.020 |
|
45° Long Radius Band |
0.010 |
|
Reducer (d/D = 3/4) |
0.007 |
FLOW NOMOGRAM
Back to previous page
|