Our Pipe Flow Expert software uses the Darcy-Weisbach formula for calculating the pressure drop in each pipe, where the friction factor is calculated using the Colebrook-White equation. This method assumes that the density of the fluid remains constant and does not change as it flows through the pipes in the system.

The Darcy-Weisbach method provides accurate results as follows :-

For incompressible systems:

Pipe Flow Expert results will always be appropriate since the Darcy-Weisbach method provides very accurate results for non-compressible fluids (including most process fluids).

For compressible gas systems the following conditions apply:

If the calculated pressure drop is less than 10% of the inlet pressure, then a reasonable accuracy will be obtained if the specified fluid density is based upon either the inlet or the outlet conditions.

If the calculated pressure drop is greater than 10% of the inlet pressure, but less than 40% of inlet pressure, then reasonable accuracy will be achieved if the specified gas density is based on the gas condition at the average of the inlet and outlet pressures. i.e. if the gas density is specified as it would be at the average pressure condition in the pipe.

In Summary

The Darcy-Weisbach method provides satisfactory results for compressible fluids when the pressure drop through the pipe system is less than 40% of the inlet pressures and the average density of the gas is used to define the system fluid.

[ Return to Pipe Flow Expert FAQs ]