Gas bubbles effect on the vibration parameters of the Coriolis flowmeter measuring tubes

In developing a methodology for measuring the mass flow rates of liquid-gas flows by Coriolis mass flowmeters (CMF), an attempt is made to estimate the effect of the presence of gas bubbles on the observed parameters of the vibrations of the CMF measuring tube. The finite-element model CMF with a straight tube, created in MATLAB package, is presented. The fluid flow is described in the 1D-approximation, the presence of a gas bubble is modeled by a local change in the flux density at the bubble location at a given time (the size of the bubble depends on the size of the finite element). Bending vibrations of the tube are carried out by means of an external harmonic force applied at the center of the tube. The drive frequency is set equal to the modal frequency of the filled tube. A series of numerical experiments has been performed, in which the gas volume fraction (GVF) and the fluid velocity varied. The dependence of the phase shift between the flowmeter arms oscillations caused by the Coriolis effect on these factors has been revealed. The error in determining the mass flow due to the bubbles presence is estimated. A series of experiments has been conducted with an industrial DU15 flowmeter to observe bubble effects. The results of the experiments are compared with the predictions of numerical calculations and their qualitative agreement is found.