Primary standard for the calibration of refrigerant leak flow rates

Abstract

Leak detection is widely used nowadays in various fields such as the automotive and refrigeration industries. The leak tightness of installations charged with refrigerants must be controlled periodically by refrigerant gas detectors, qualified by refrigerant leaks called reference leaks or 'calibrated' leaks. To this day, those refrigerant leaks are not traceable to the SI units under their operating conditions. Therefore, a project involving the LNE, the CEP and the ADEME was initiated in order to develop a national standard for calibrating refrigerant reference leaks.The method consists in measuring the accumulation of gas due to the refrigerant leak inside a closed volume at atmospheric pressure. The leak flow rate is deduced from the concentration variation, measured with a photo-acoustic spectrometer, the pressure and temperature in the accumulation volume and the capacity of the accumulation volume. The uncertainty budget thus takes into account the measurement uncertainties of these quantities. The main components of the uncertainty are due to the accumulation volume capacity and the measurement of concentration. The relative expanded uncertainty of leak flow rates between 1 g yr −1 and 50 g yr −1 is around 2%, depending on the value of the leak.

Monte Carlo Method Applied to Gravimetric Leak Calibration

“…The leak value is simply given by the change in mass during a given time interval. At any given time, the mass 𝑀 of the leak is given by equation (1).…”

“…The leak tightness of installations charged with more than 3 kg of refrigerants must be controlled periodically by leak detectors with a detection limit of 5 g•yr -1 and qualified by means of traceable reference leaks. LNE developed in 2008 a national standard for calibrating refrigerant leaks, based on the measurement of the concentration of the gas emitted by the leak in a volume by means of a photo-acoustic spectrometer [1]. If this reference is suitable for calibrating reference leaks with adapted uncertainties, it requires an important investment in terms of cost and its implementation is time consuming.…”

Leak rate metrology for the society and industry

“…Other type of primary method consists in measuring the concentration rise of the tracer gas emitted by the refrigerant leak inside a known volume. The rise of the refrigerant gas concentration is then measured by an photo-acoustic spectrometer [30].…”

Perspectives of atmospheric reference leaks calibration by gravimetric method

“…The primary leak standards working at the atmospheric pressure can be divided into those being sensitive [1] and being insensitive [2][3][4][5][6][7][8] to a detected gas species. The problem of the first group is that they can work only with a limited number of gases, the problem of the second group is that they measure depleted amount of gas, i.e.…”