Metrological studies of a reference installation for reproducing the mass flow of humid air

The relevance of the development and metrological studies of reference installations when working in a humid gas medium is considered. The concept of creating a reference installation for reproducing the mass flow of humid air is outlined. An algorithm for the operation of a reference installation has been developed, which provides for the generation of water vapour as a component of the gas flow. Based on the algorithm and operation features of a reference installation, a list of the considered type A uncertainties, which relate to the estimation of the air volume measured by a reference meter, duration of the control volume reproduction, mass of generated water vapour during the period of reproduction of the volume, and relative humidity of the ambient air, was formulated. Type B uncertainties are considered, which are determined by metrological characteristics of the used measuring equipment: reference gas meter, chronometer, hygrometer, manometer, thermometer, and instruments for measuring the mass of generated moisture. Algorithms for evaluating the standard uncertainty by using the standard reference data are given: pressure and density of saturated water vapours, and air density under standard conditions. The formula and algorithm for its metrological evaluation based on the uncertainty theory for determining the compressibility coefficient of the ambient air used during the operation of the installation, taking into account its relative humidity, are also presented. The expressions for evaluating the combined and extended uncertainties of the developed installation are given. The developed model relates to the mass measurement of wet gas and allows assessing the influence of operating conditions of the installation on the indications of the mass flow measuring equipment of various operating principles, for example, thermo-anemometric, ultrasonic. The developed metrological model can be used to estimate metrological characteristics of reference installations operating in different types of gaseous medium, including natural gas.