voomaht, kus voolava keskkonna vookogus on väljendatud massina, quantity equal to the mass dm of substance crossing a given surface during a time interval with infinitesimal duration dt, divided by this duration, thus qm = dm / dt, flow rate in which the quantity of fluid is expressed as mass, mass of the gas passing through the critical flow nozzle per unit time, mass of fluid which passes per unit time, mass of fluid passing through the primary device per unit time