Pipe Flow Expert will detect sonic flow situations when the Specific Heat Ratio of the gas is defined, and the Compressible Gas Flow Calculation Engine is used to solve the system.

The specific heat ratio is used to calculate the sonic velocity for a particular gas at a given temperature and pressure condition and the software will check whether sonic flow will occur anywhere within the pipe network once the solution has been calculated. If sonic flow does occur, Pipe Flow Expert will show a warning message stating that it cannot solve this system.

The compressible flow equations assume isothermal flow, which means the fluid temperature is assumed to remain at the defined temperature. If large changes in pressure in the system cause the temperature of the gas to change significantly then the user would need to account for this, possibly by introducing different fluid zones in to the system where the gas properties are defined for different temperature conditions.