## Can Pipe Flow Wizard Software handle compressible fluids?

The Pipe Flow Wizard software uses the Darcy-Weisbach formula to calculate flow and pressure losses in pipes. This formula can be used for pressure loss calculations of any Newtonian fluid where the viscosity and density is known.

When calculating a pressure loss for gases the reference density at 0.000 barg is used with the ideal gas law to calculate the density of the gas for the entry condition.

The Darcy-Weisbach formula can be used for calculating pressure losses involving compressible fluids, but some cautions are appropriate:

1) The effect of temperature changes is not modelled.

2) If the calculated pressure drop in the system is less than 10% of the pressure at the compressible fluid entry points, then a reasonable accuracy of the results may be expected.

3) Where the pressure loss in any section of a pipe is higher than 10% of the highest pressure in absolute pressure units (e.g. if 10 psi gage was the highest/start pressure then this is actually 24.696 psi absolute and thus a pressure drop of 2.4 psi would be less than 10% of start condition in absolute pressure) but less than 40% of the highest pressure in that section, the calculated results could use the averaged density of the fluid in the pipe in order to generate an industry accepted accuracy, however at present Pipe Flow Wizard uses the calculated density at the start condition, and therefore for pressure drops of greater than 10% of the absolute start pressure we recommend considering the pipe as a series of sections and the outlet pressure from one section should be used as the entry pressure for the next section.

4) The Pipe Flow Wizard software does not detect sonic flow situations.

It would be up to the user to determine the LOWEST temperature that can occur in the pipe (due to lowering of the gas pressure and the increase in velocity) so that an appropriate sonic velocity limit can be manually calculated. The MAXIMUM velocity in the pipe would then need to be checked to ensure that the design is not approaching a 'Choked Flow' condition.

The Pipe Flow Wizard software (for single pipes only) allows users to enter either normal or compressed volumes and the software automatically calculates the density of the compressed gas from the uncompressed gas density data using the ideal gas law.

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