Which fluids does Pipe Flow Expert support?
The Pipe Flow Expert software comes with its own fluid database of common liquids and gases. It also contains some functionality that allows users to calculate new gas data for specific temperature and pressure conditions.
If your pipe system contains a fluid that is not present in the fluid database then you can simply add your fluid and its properties, and this data can then be used by the program.
Pipe Flow Expert allows up to 9 dfifferent fluid zones to be defined across a pipe system and the fluid for each zone can be individually specified. Once a fluid is selected from the fluid database the software will then automatically use the associated properties of the fluid when performing the system flow and pressure drop calculations.
Pipe Flow Expert performs pressure drop calculations using the Darcy-Weisbach equation to calculate friction loss, where the friction factor is calculated using the Colebrook-White equation. The Darcy-Weisbach equation provides very accurate calculation results for incompressible Newtonian fluids, since the density of these fluids can be considered to be constant.
However, since the Darcy-Weisbach equation assumes a constant density and viscosity, the calculations do not automatically take account of any compression or expansion of the fluid that may occur due to tempertaure and pressure changes in the fluid. While it is still common practice for the Darcy-Weisbach equation to be used to calculate the friction losses for compressible fluids (such as gases) within a pipeline system, there are certain modeling constraints that should be understood.
More information on 'Working with compressible fluids' is provided in the Pipe Flow Expert User Guide. In short, if the calculated pressure drop in an individual fluid zone in the system is less than 10% of the pressure at the compressible fluid entry points into the individual fluid zone, then a good accuracy of the results may be expected. If the calculated pressure drop in an individual fluid zone in the system is greater than 10% but less than 40% of the pressure at the compressible fluid entry points into the individual fluid zone then the Darcy-Weisbach equation will give a reasonable accuracy provided that the calculations are repeated using the average density of the individual fluid zone.
It is up to the pipe systems engineer to be familiar with good engineering practice and to use their own judgment in regard to the accuracy tolerance of the calculated flow rate and pressure drop results for a system that contains a compressible fluid.
