Description

The BS sonic nozzles are designed to provide constant flows of clean and dry gas within a range of 1 Nml/min to 20 L/min. There are 2 kind of sonic nozzles (ISO 6145‐6 technology):

‐ The “calibrated sonic nozzle” is used for supporting reference stream. In this case the manufacturing tolerance is about 2%. In addition, the real flow is measured with a traceable volumeter with an accuracy of 0.2%.

‐ The “non calibrated” is used for supporting leak stream at working pressure. In this case the manufacturing tolerance is about +/‐ 10 %.

Functioning principle

The BS sonic nozzle is an one way device, with divergent orifice protected by a stainless filter.

A gas stream through a nozzle is called “sonic”, when the fluid flow speed reaches its own sonic speed at the minimal cross section.

This speed is reached when the ratio between the input absolute pressure P1 to the output absolute pressure P2 correspond to the expression :P1/P2≥2

The mass flow Qm for a nozzle working at a sonic range is given by :  

Where Kgaz is a physic constant for a specified nozzle and used gas, T is the absolute temperature at the minimal cross section.

The mass flows ratio of different gases flowing through the same nozzle, with the same pressure and temperature, is defined by the ratio of the Kgaz constants.

The mass flow for sonic nozzle is not influenced by the outlet pressure P2 . This characteristics provide various and numerous applications in the field of stream control and gas mixing. The calibration is performed with Nitrogen at a fixed pressure (various gases, different from N2, can be requested for the calibration).