Mass Flow Rate

mass flow rate is the mass of a substance which passes per unit of time. Its unit is kilogram per second in SI units, and slug per second or pound per second in US customary units. The common symbol is (ṁ, pronounced "m-dot"), although sometimes μ is used. Sometimes, mass flow rate is termed mass flux or mass current.

Mass flow devices are used for applications requiring high accuracy, precision measurement and control of the flow of gas molecules. There are so many applications that benefit from measuring and controlling mass flow, from bioreactor outgassing to fuel cell membrane testing to natural gas monitoring.

Mass flow rate is important precisely because of the ways it differs from volumetric flow: it is standardized, and will not fluctuate with changes to ambient temperature or pressure.

Mass flow rate depends on the density of the gas that is being flowed. For laminar differential pressure devices, it is important to know the exact composition of the gas being flowed so that precise density corrections can be made.