Investigating flow measurement using flush mounted ultrasonic transducers

Accurate and reliable measurements of fluid flow are significant in fields such as oil and gas, water supply, aerospace, chemical and pharmaceutics. Demand for high-accuracy flow measurement has recently expanded into the measurement of greenhouse gases emitted from smoke or flare stacks to facilitate better management and reduction of emissions for a sustainable society.

Ultrasonic transit-time (TT) flow measurement is well-established, and has been used by many flow meter manufacturers. In an ultrasonic flow meter, two contra-propagating ultrasonic waves are transmitted and received through the same path by a pair of ultrasonic transducers where one is placed upstream of the other. Measuring these two opposing TTs provides a quantitative measurement of the path-averaged (PA) flow velocities along the ultrasonic path.

By using multiple pairs of transducers and configurations of paths, together with suitable correction factors or numerical integration algorithms, one can calculate the area-averaged (AA) flow velocity and flow rate down a pipe.

In practice, four sources of error significantly reduce the accuracy of the conventional ultrasonic TT flow meters. First, the transducers have to be mounted via an inclined hole in a meter body and the cavities that the transducers sit in cause local vortices and turbulence, undermining the accuracy of the flow measurement. Second, the TTs measured by the transducers is significantly influenced by the dynamic performance of the transducers. Any inconsistency or variations in the performance due to the fluctuation of operating conditions will further reduce the measurement accuracy. Third, if the actual velocity profile of the flow is different from the profile used in the calibration process, significant errors will be introduced when calculating the AA flow velocity based on the measured PA flow velocities. Finally, the ultrasonic path is refracted when propagating through a fluid flow
due to the non-uniform velocity profile. But the ultrasonic path is considered as a straight line in conventional flow meters, introducing additional measurement errors.

New flow metering technology will be investigated to increase the accuracy of ultrasonic flowmeters. Transducers able to efficiently operate when mounted flush with an inner wall of a pipe will be created and tested. That could eliminate the measurement error caused by the disturbance of the transducer installation. The new ultrasonic transducers will simultaneously measure the ultrasonic signals travelling via different paths, so more flow information can be obtained. Moreover, the difference in the TTs of the ultrasonic signals transmitted and received by the same pair of transducers is not influenced by the transducer performance, and thus will significantly improve the measurement accuracy of the average flow velocities along the ultrasonic path (the PA). As much more information can be extracted via FUTs, accurate reconstruction of the actual flow velocity profile using refraction tomographic technology will be conducted, which can greatly reduce the errors in the calculation of the AA flow velocity in a pipe.

This fellowship follows the research in the EU project (Steerable Air-Coupled Ultrasonic Technology for Flow Measurement and NDE Applications) and the EPSRC project (High Frequency Flexural Ultrasonic Transducers), where I have developed a group of novel flexural ultrasonic transducers.

This research focuses on minimising the sources of error which conventional flow meters experience and will lead to a new generation of high-accuracy ultrasonic flow metering technology.

The fundamental research has commercial value, and will generate research outputs and social and economic impact.