Transit-time ultrasonic flow metering relies on the flow profile correction factor (FPCF) to improve its measurement capability by converting line-integrated flow velocity into area-integrated flow velocity. It is because the flow velocity is integrated along ultrasonic paths between ultrasonic sensors by sending and receiving pulse signals in the transit-time ultrasonic flow metering. ISO 12242 (liquid flow metering) and ISO 17089 (gas flow metering) specify how to define the FPCF with a transit-time multi-path ultrasonic flow meter. The FPCF is applied to an averaged value of line-integrated flow velocities, not to each line-integrated flow velocity, according to the ISO standards. The present use of FPCF is validated in the fully-developed turbulent pipe flow, which a long straight pipe is installed upstream of the ultrasonic flow meter. However, the present FPCF would not be very accurate in asymmetric pipe flows with various conduit elements, such as elbows.

This study attempts to apply the FPCF to each line-integrated flow velocity in transit-time multi-path ultrasonic flow metering. The FPCF can be applied to each line-integrated flow velocity if the FPCF is based on flow velocity distribution functions, such as those suggested by Salami (1984). The Salami’s flow velocity distribution functions include one symmetric flow, three one-peak flows, and two two-peak flows. The FPCF is calculated by line-integrals along the ultrasonic paths on each flow velocity distribution function. This study is the first attempt to show that the FPCF can be applied to convert the line-integrated flow velocities into the area-integrated flow velocity along each ultrasonic path.

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