How the Sonic Nozzle Calibration Device Works

1. Gas Flow through the Nozzle:

   • The device works by forcing gas through a precisely designed sonic nozzle. A sonic nozzle is a flow restriction with a specific shape and dimensions that, when operated at a particular pressure, causes the gas to reach sonic speed (Mach 1) at the nozzle throat.

2. Choked Flow Condition:

   • When the gas flows through the nozzle at this sonic condition, the mass flow rate becomes a function of the pressure upstream of the nozzle and the nozzle’s geometry, which is precisely known and can be calculated.

3. Measurement of Flow:

   • The pressure and temperature of the gas upstream of the nozzle are carefully monitored and controlled.
   • Since the flow rate through the nozzle is determined by the upstream pressure (and temperature), it provides a very accurate and known reference flow that can be used to compare against the reading of the gas flow meter being calibrated.

4. Calibration:

   • The gas flow meter is placed downstream of the sonic nozzle, and its readings are compared to the flow rate established by the nozzle.
   • Adjustments or calibration of the meter are made based on the deviation between the meter reading and the known flow rate.

5. Accuracy:

   • The sonic nozzle provides very precise flow measurements, often with accuracy better than 0.5%. This high level of accuracy makes it an ideal tool for calibrating highly sensitive and precise gas flow meters, such as those used in laboratory environments, calibration facilities, and process industries.