Effects of Velocity Profiles on Measuring Accuracy of Transit-Time Ultrasonic Flowmeter

Abstract

Ultrasonic wave carries the information for flowing velocity when it is propagating in flowing fluids. Flowrate can be obtained by measuring the propagation time of ultrasonic wave. The principle of transit-time ultrasonic flowmeters used today was based on that the velocity is uniform along the propagation path of the ultrasonic wave. However, it is well known that the velocity profiles in a pipe are not uniform both in laminar flow and turbulent flow. Emphasis on the effects of velocity profiles across the pipe on the propagation time of ultrasonic wave, theoretical flowrate correction factors considering the real velocity profile were proposed for laminar and turbulent flow to obtain higher accuracy. Experiment data of ultrasonic flowmeter and weighting method are compared to verify the proposed theoretical correction factors. The average relative error of proposed correction factor is determined to be 0.976% for laminar flow and 0.25% for turbulent flow.

Liquid Flow Measurement Using Silicone Polymer Wedge Clamp-On Ultrasonic Transducers

“…The small DC voltage offset from the amplifier was removed so the signal always oscillates about the zero voltage point. The mass flow rate measured by CUTs can then be calculated using Equations (6), (8) to (10).…”

“…where Re is the Reynolds number;  is the liquid density (kg/m 3 );  is the dynamic viscosity (Pa• s). It can be seen that the ultrasonic wave travels through the flow with varying local velocities which the transducers measure as a line-average velocity [8]. This average however fails to account for the actual velocity distribution across the pipe cross section which in reality is two dimensional [21].…”

“…CUTs have been developed for about 70 years [7] and different mechanisms have been adopted to measure liquid flow rate, such as Doppler, cross-correlation and transit-time measurement [7,8]. While Doppler CUTs remain an excellent solution for dirty liquids [9], transit-time CUTs have been showing faster growth in recent years due to their high accuracy [10,11].…”

“…In this preliminary experiment, a constant FPCF in equation(9)was used to calculate the mass flow rate. But this correction factor varies with Reynolds number[8] and it should be adjusted with varying flow rates to improve the measurement accuracy.…”

Multi-Angle Liquid Flow Measurement Using Ultrasonic Linear Array Transducer

“…However, the accuracy of the Doppler ultrasonic flowmeter is limited by its dependence on the properties of the particles (e.g., size, concentration, distribution, and the relation between particles and fluid velocity) [11]. The second type is the transit-time ultrasonic flowmeter, which calculates the flow rate according to the differential transit time of the reflected ultrasonic waves between the downstream and upstream flow of the liquid [12][13][14]. The reflection of ultrasound waves is mainly due to the impedance mismatch between the pipe walls and the fluid.…”