Diagnosis of aerated flow at water line with Coriolis flowmeter using Hilbert transform

A Coriolis mass flowmeter provides highly accurate measurements of single-phase flows, regardless of the flow properties. However, an aerated flow causes significant measurement errors in this flowmeter. In order to diagnose the aerated flow in a waterline by using a Coriolis mass flowmeter, this study focuses on three factors: the amplitudes of two sensor coil signals (hereafter A, B) and the phase difference ΔΦ between them. The study suggests that the fluctuation in the function, which is obtained through the process of phase difference calculations using Hilbert transform, can be used to diagnose the aerated flow at any operating points. Through the experimental investigations, the following facts are established: (1) The RMS of the second order difference in our proposed index increases with the void fraction, and (2) the RMS is approximately 0 in a single-phase flow at any operating points. These results show that this diagnostic index can be used to distinguish a single-phase flow from an aerated flow. In addition, it is also clarified that the flow measurement error that occurs with an increase in the void fraction can be evaluated by using Hilbert transform, regardless of operating points.