Definition(s)
Mach Number
Actual fluid velocity divided by the velocity at which sound waves propagate through the fluid at the associated temperature.
Source: API STD 521, Pressure-relieving and Depressuring Systems, Sixth Edition, January 2014. Global Standards
Mach Number
Ratio of a fluid’s velocity, measured relative to some obstacle or geometric figure, divided by the speed at which sound waves propagate through the fluid.
Source: API STD 521, Pressure-relieving and Depressuring Systems, Fifth Edition, January 2007 (Addendum May 2008). Global Standards