Modeling of the Flow Comparator as Calibration Device for High Pressure Natural Gas Flow Metering in Modelica

摘要

The German national metrological institute, Physikalisch-Technische Bundesanstalt, is developing a new concept for volumetric primary standard to calibrate high pressure gas flow meters. The TUHH is supporting these R&D activities with its competence to elaborate computational models for detailed analysis of complex electromechanical systems including fluid flow aspects. The new primary standard is called Flow Comparator and uses an actively driven piston prover to measure the gas flow rate using the time the piston needs to displace a defined enclosed volume of gas in a cylinder. In Modelica a computational model is developed to investigate the Flow Comparator's dynamic behaviour and interaction with the other components in the loop. Furthermore, it allows to gather detailed information about pressure and temperature development at arbitrary chosen locations in the system with high time resolution. The validation of the developed model shows good compliance with measured piston velocity and differential pressure at the piston. The model is used to optimize the frequency inverter's control voltage trajectory to increase the available measuring time.