Design of a Flowrate Measurement System for Low-Pressure Gases

Design of a flow meter to be used in a low-pressure environment is hereafter presented. The need of this activity comes from the lack of commercial flow meters operating at low pressures due to the unusual working environment, where outgassing and sublimation phenomena becomes relevant for many materials and rarefied atmosphere changes dramatically the heat and mass exchange phenomena. In our case, the need of a low pressure compatible measurement system comes from the need of measuring the flow rate of a rotary vane pump working under an environmental pressure between 10 and 6 mbar, simulating the condition of the Martian atmosphere at the surface. The pump will be the key component of a particle analyzer that should be part of the ExoMars 2020 ESA-Roscosmos mission. The designed measurement system is based on the deformation of a control volume, a stainless-steel bellow, which has been designed on the basis of the expected flow rate. The measurement system has been calibrated at ambient condition and testing in low-pressure has been performed in order to validate the measurement method and derive the flow rate performances within the expected working conditions.