Sonic Nozzle Features:
A sonic nozzle works is a gas flow limiting device which works according to the principle of critical flow or choked flow. When a gas is accelerated to sonic velocity through the nozzle, its mass flow-rate becomes independent of variations in downstream conditions.
Working Principle:
Fluid flows through the nozzle from the high pressure chamber to the low
pressure region. The pressure at intake is called stagnation pressure and the pressure at exit is called back pressure. When we start to reduce the back pressure, the flow velocity and mass flow rate also starts to increase. But this will only happen up to a certain limit. At that limit, the flow velocity will be equal to the velocity of sound. Beyond this limit, no changes will occur in flow velocity and mass flowrate. This is known as the choked condition and uniform mass flowrate is maintained.
Advantages: Differential pressure measurement not required Flow rate is not affected by downstream flow disturbances Mass flowrate varies linearly with inlet pressure Minimal upstream piping required.
Differential pressure measurement not required 
