## Can Pipe Flow Expert handle fluids with different density and viscosity properties?

Yes. For liquid systems, the Pipe Flow Expert software uses the Colebrook-White equation to calculate friction factors and these are then used in the Darcy-Weisbach formula to calculate the pressure drop in a pipe. These formula provide the most accurate results possible for non-compressible Newtonian fluids. For gas systems, the Pipe Flow Expert software uses the Colebrook-White equation to calculate friction factors and these are then used in a chosen compressible flow equation such as the General Fundamental Flow equation, Complete Isothermal Flow equation, AGA equation, Weymouth equation, or Panhandle equation.

**Non-Compressible Fluids**

The Darcy-Weisbach equation assumes a constant fluid density and viscosity, as occurs in a system with a non-compressible fluid (generally a liquid). Pipe Flow Expert can be used for all systems with non-compressible Newtonian fluids, whether low pressure or high pressure, and whether the pipe sizes are large or small.

**Compressible Fluids**

For compressible fluids (generally gases), Pipe Flow Expert now contains a specialist compressible gas flow calculation engine, which allows a choice of compressible flow equation to be used when solving the pipe network. The software automatically takes account of density changes within the gas throughout the network.

For further detailed information on calculations for compressible fluids (gases) see http://www.pipeflow.com/software-technical-support/compressible-flow-calculation

**Compressible Fluids (using non-compressible calculation equation)**

Pipe Flow Expert can also calculate for compressible fluids (gases) using the non-compressible Darcy-Weisbach equation. Engineers sometime uses this for low pressure, low velocity gas systems, however we recommend always using the Compressible Flow Calculation Engine when working with gas systems. The results obtained from the Darcy-Weisbach equation provide industry accepted accuracy if the pressure loss is less than 10% of the starting pressure and the density and viscosity of the gas at the starting pressure condition are used in the calculations. If the pressure drop is greater than 10% of the starting pressure (in absolute terms) but the pressure drop is less than 40% of the starting pressure (in absolute terms) then industry accepted accuracy is obtained if the density and viscosity of the gas at the average pressure condition within the pipe is used in the calculation.

As stated, Pipe Flow Expert now contains a Compressible Gas Flow Calculation Engine and we would strongly recommend using this for calculating gas systems (this is now the default calculation engine for gas systems) rather than using the non-compressible calculation engine which is based on the Darcy-Weisbach equation (mainly used for non-compressible liquid systems).

**Fluid Zones**

Pipe Flow Expert uses the concept of "fluid zones" to allow construction of systems where different sections - fluid zones - have different fluid properties (different density and viscosity data) that are used for the calculations within that section of the network.

Fluid zones allow calculations on system which contain different fluids. The software does not automatically calculate the properties for mixed fluids, however the fluid zones allow the user to define different sections of their network with different fluid properties. For example, the user could define a system where two different oils mix and then continue on within the system. The user would define three fluid zones, one for each of the original oils and then a third one for the mixed oil. Each fluid zone would specify the density and viscosity of the fluid in the system at that point. The Pipe Flow Expert software calculations run on mass flow and therefore the program is able to handle the different fluid properties to correctly calculate a result that ensures the mass flow in and out of any node is the same (as required by the conservation of energy principle).

Fluid zones also allows the user to split up a gas network such that the fluid properties for a particular section of the gas network represent the approximate average density and viscosity of the gas for that section, which ensures an acceptable accuracy in the pressure drop calculation for a compressible fluid (provided that the pressure drop is less than 40% of the absolute start pressure within that section).

**Slurries**

We do not offer an special calculation method for slurries and therefore we do not normally recommend the software for slurry applications, however, if you know the density and viscosity of the slurry, and the fluid velocity is sufficiently high, such that it keeps any solids in suspension (so that the fluid can be considered Newtonian) then the Darcy-Weisbach formula can be used to calculate the flow rates and pressure drops in the piping system, and in this case the software would provide a good modeling solution.

**Gases**

Pipe Flow Expert is used to calculate the flow and pressure drop results for gas systems but the users must ensure that the system falls within the criteria that are detailed here http://www.pipeflow.com/software-technical-support/compressible-flow-calculation

There is also a section in the Pipe Flow Expert User Guide about working with compressible fluids.