Improved critical flow factors and representative equations for four calibration gases

The critical flow nozzle is widely used to calibrate flowmeters in gas Row measurement. Its use requires the critical how factor, C*, a parameter depe ndent upon the thermophysical properties of the gas at the nozzle throat, a nd the upstream temperature and pressure. This paper presents C* values for four calibration gases (air, argon, nitrogen and methane), calculated from the most recent reference quality equations of state, over a wider range o f temperature and pressure than previously available, 200-600 K and up to 2 0 MPa. In addition, a new empirical equation has been developed to represen t the calculated values accurately, thus eliminating the need for complex c alculations or interpolations from tables. (C) 1999 Elsevier Science Ltd. A ll rights reserved.