Institute of Modern Physics, Chinese Academy of Sciences is developing a high-precision calibration device for lead-bismuth flowmeters based on the static mass method. In static mass method-based calibration devices, the uncertainty component of the diverter is the main component of the uncertainty of the flowmeter calibration device.

This study aims to predict the system error of a cylinder-driven diverter due to the asymmetry of cylinder forward and reverse strokes in the calibration process of lead-bismuth flowmeters, realize the a priori analysis of class B uncertainty components of a cylinder-driven commutator, and investigate whether the class B uncertainty can accurately reflect the magnitude of the relative system error introduced by the diverter.

Firstly, a two-way coupling calculation method based on computational fluid dynamics (CFD) was developed for the diverter, and the SST k-ω turbulence model and Euler multiphase flow model were employed for calculation. Then, the stroke difference method was employed to obtain the class B uncertainty components for the diverter under different flow conditions and torque drives, and the calibration relative system errors under different timing methods and velocity distributions at the commutator nozzle outlet were calculated. Finally, the operating characteristics of the cylinder-driven diverter were analyzed.

Computation results show that the greater the thrust of the cylinder, the smaller is the type B uncertainty of the diverter. Compared to using the start or end of stroke as the timing moment, the calibration error caused by the diverter is the lowest when the diverter baffle is moved to the midpoint of the stroke as the timing moment, and the error is approximately 1/7?1/30 times those of the other two timing methods. The magnitude of diverter class B uncertainty reflects the envelope value of the relative systematic error caused by the diverter when using different timing moments.