Flow rate measurement of gaseous nitrogen *

* in the manufacturing process for semi-conductors

BACKGROUND

Flow rate measurement of ultra pure nitrogen on the production line for semi-conductors. Ultra pure nitrogen is used to remove impurities following the silicon etching process performed on high frequency integrated circuits intended for telephone applications.

DESCRIPTION OF THE APPLICATION

The measurements must be performed with a maximum pressure of 7 bars, at a maximum gross flow rate of 5m3/hr. To adapt quickly to the gas network to be measured, “Swagelock” quick-fit connections are used. This measurement must have a minimum loss of pressure and present no risk whatsoever in terms of contamination of the gas.

EQUIPMENT USED

Minisonic P converter Pipe-spool measurement
Convertisseur Portable MINISONIC P Manchette de mesure
This is a portable measuring device. Custom-made for the client, it consists of a stainless steel body with an inner diameter of ¾”, in which 500KHz probes are inserted.

RESULTS

Fitting in reflex configuration enables the acoustic path to be increased whilst minimising the straight lengths, which means that greater accuracy can be achieved, complying with the specifications of the customer (see COFRAC results below).

Results of the COFRAC calibration tests performed at CETIAT

Qmr (kg/s) ρ (kg/m3)  Qvr (dm3/h) Qvd (dm3/h) % error Upstream absolute pressure (Pa)
 2,049e-3  7,036  1048,4  1047  -0,1  597251
 2,066e-3  7,033  1057,5  1056  -0,1  597123
 3,933e-3  7,027  2015  2011  -0,2  596623
 3,961e-3  7,025  2030  2036   0,3  596349
 6,867e-3  7,010  3527  3533   0,2  595108
 6,926e-3  7,015  3554  3546  -0,2  595688
 9,630e-3  6,997  4955  4978   0,5  593988
 9,678e-3  7,001  4977  4974  -0,1  594588

Key:
Qmr: reference mass flow
p: density
Qvr: reference volumetric flow
Qvd: flow meter volumetric flow

ADVANTAGES

The mechanical study, Ultraflux’s expertise in hydraulics and the care taken in producing the sleeve ensured that there was virtually no loss of pressure.