What is the difference between volume flow and mass flow?

Coriolis flow meters measure real mass flow, whereas thermal mass flow meters are dependent of the physical properties of the fluid. True mass flow measurement is an important development across industry as it eliminates inaccuracies caused by the physical properties of the fluid, not least being the difference between mass and volumetric flow. Mass is not affected by changing temperature and pressure. This alone makes it an important method of fluid flow measurement.

Volumetric flow remains valid, in terms of accuracy, provided that the process conditions and calibration reference conditions are adhered to. Volumetric measuring devices, such as variable area meters and turbine flow meters, are unable to distinguish temperature or pressure changes.