The Pipe Flow Expert software now contains a Compressible Isothermal Flow Calculation Engine (from version 7 and later).


In a gas system, as pressure loss occurs along a pipe, the gas density will decrease and the volume of the gas will expand. As the volume of gas increases, the velocity of the gas in the pipe will increase. Although the volume of gas and velocity in the pipe changes, the mass flow (weight of flow) in the pipe will remain constant.


Gas flow rates are therefore often referred to in terms of mass flow (weight of flow) or standard volume (which is the volume of gas at standard conditions, normally atmospheric pressure and some common temperature reference, since this standard volume also define a constant mass flow).


Pipe Flow Expert provides a choice of standard volume units for gas flow rate which include:


  • SCCM (Standard Cubic Centimeters per Minute), 
  • SLM (Standard Liters per Minute), 
  • SCMH (Standard Cubic Meters per Hour)
  • MMSCMH (Million Standard Cubic Meter per Hour)
  • MMSCMD (Million Standard Cubic Meter per Day)
  • SCFM (Standard Cubic Feet per Minute)
  • SCFH (Standard Cubic Feet per Hour)
  • SCFD (Standard Cubic Feet per Day)
  • MMSCFH (Million Standard Cubic Feet per Hour)
  • MMSCFD (Million Standard Cubic Feet per Day)


Each of the standard volume units for gas flow relate to the gas at a standard condition, however there are a number of slightly different standard reference conditions that are used worldwide depending on country and location. Pipe Flow Expert provides a choice of standard reference conditions to be used when referring to the standard volume flow rate of gas and these include:


  • 0°C, 100.000 kPa.a
  • 0°C, 101.325 kPa.a
  • 15°C, 101.325 kPa.a
  • 20°C, 101.325 kPa.a
  • 25°C, 101.225 kPa.a
  • 60°F, 14.696 psi.a
  • 68°F, 14.696 psi.a


Mass flow can also be used to refer to an amount of gas flow and the units for mass flow include:


  • Kgs/sec
  • Kgs/min 
  • Kgs/hour 
  • Lb/sec
  • Lb/min
  • Lb/hour