Applicability of hybrid ultrasonic flow meter for wide-range flow-rate under distorted velocity profile conditions

Abstract

In transit-time ultrasonic flow meters (TOF), the flow rate is derived from the transit time of an ultrasonic pulse between two ultrasonic transducers. To convert the transit time into flow rate, a profile factor (PF) is required. Because the PF strongly depends on the velocity profile, a precise calibration of the PF is essential to the accuracy of the TOF. Hence, a field calibration, referred to as on-site calibration, is desirable. In this study, a hybrid ultrasonic flow meter that helps calibrate the TOF using ultrasonic Doppler velocimetry (UDV) is proposed for on-site calibration by integrating the velocity profiles over the cross-sectional area of a pipe. Thus, a new system of hybrid ultrasonic flow meter was developed. The maximum flow rate measured using a conventional UDV is significantly lower than that measured using the TOF. Therefore, a system was developed to measure higher velocities and flow rates. The system is novel in that the transit time and velocity profile can be simultaneously measured using a de-aliasing method. To evaluate the influence of the velocity profile on the PF, experiments were conducted under a wide range of flow-rate conditions, which otherwise cannot be implemented using the conventional UDV. To evaluate the influence of the velocity profile in the pipe, an obstacle plate was placed at 8D upstream the test section. Radially arranged measuring lines were employed. The experimental results show that increasing the number of measuring lines did not improve the accuracy of the TOF. On the other hand, the flow rate could be accurately obtained using the proposed UDV by measuring the velocity profile even under distorted flow conditions. Furthermore, the calibration of the PF based on the flow rate obtained using the proposed UDV was found to be feasible.