Pipe Flow Expert is a software application for designing and analyzing complex pipe networks where the flows and pressures must be balanced to solve the system. It can handle both non-compressible and compressible fluid flow.

This document relates to verification of the Pipe Flow Expert software for calculating flow rates and pressure drops for compressible gas systems.

Fluid Properties for the pressure condition at the start of each pipe are calculated from the user defined fluid data using the Ideal Gas Law plus any specified Compressibility Factor Z to establish the density of the gas. 

Ideal Gases are considered to be perfectly elastic. Ideal gases follow Boyle’s Law & Charles’s Law thus the gas density at various points in the system can be calculated using these equations. 

Real Gases behave according to a modified version of the ideal gas law. The modifying factor is known as the Gas Compressibility Factor Z. Where natural gas pressures are higher than 115 psi.a (800 kPa.a) the gas compressibility factor may not be close to 1.00, so it can be advisable to use a gas compressibility factor based on the pressure in the pipe. 

There are different methods that can be used to calculate a gas compressibility factor for a specific pressure condition. The California Natural Gas Association (CNGA) method provides such a calculation for natural gas. The Pipe Flow Expert software includes the option to automatically use the CNGA method to determine the natural gas compressibility for the average conditions in each pipe. The CNGA factor is then applied when calculating the gas flow rate using a specific Isothermal Flow Equation that allows for gas compressibility. The CNGA compressibility factor is only applicable to natural gas and is not applicable to other gases such as air etc.

The General Fundamental Isothermal Flow Equation (sometimes known as just the General Flow equation or the Fundamental Flow equation) provides perhaps the most universal method for calculating isothermal flow rates, however it relies on the inclusion of an accurate friction factor. The Pipe Flow Expert software provides such a friction factor by calculating this using the Colebrook-White equation. For complex interconnected pipe systems this equation provides perhaps the best overall calculation result, however this approach is only made possible by the advanced software algorithms and the power of computer calculation.

In addition to this general flow equation, Pipe Flow Expert provides the functionality to allow calculations based on alternative equations such as:

The Complete Isothermal Flow Equation (as defined in Crane Technical Paper 410)

The AGA Isothermal Flow Equation, 

The Weymouth Isothermal Flow Equation

The Panhandle A Isothermal Flow Equation,

The Panhandle B Isothermal Flow Equation.

The IGT Isothermal Flow Equation.

Each of these equations can be used to calculate isothermal flow rates in pipes. Most of these equations use a Pipeline Efficiency factor (instead of a friction factor) and a Compressibility factor. The software allows the user to specify these factors and these are then used in the calculations.

Flow and Pressure Loss Calculations produced by the Pipe Flow Expert software can be verified by comparison against published results from a number of well-known sources. The information in this document provides a general description of a Published Problem, the Reference Source, the Published Results Data, the Pipe Flow Expert Results Data and a commentary on the results obtained.

The Pipe Flow Expert Results Data compares very well with the published results data for each of the cases that are listed. 

We have clients in a variety of industries including aerospace, chemical processing, education, food and beverage, general engineering, mining, petrochemical, pharmaceutical, power generation, water and wastewater processing

Pipe Flow Expert is currently used by engineers in over 75 countries worldwide.