Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Engineering Science

Program

Mechanical and Materials Engineering

Supervisor

Savory, Eric

Abstract

The clamp-on ultrasonic flowmeter measures the fluid flow velocity and flowrate with the help of ultrasonic waves. Flow profile distortion due to pipe network disturbances cause uncertainty in the flowrate measurement. A numerical and experimental investigation is conducted to model the performance of a clamp-on ultrasonic flowmeter onto a straight pipe and at x/d=1 downstream of a 900 elbow for the flowrate range of 0.3-2.5m3/hr. The average percentage error in the flowrate at x/d=1 downstream of the elbow estimated from the numerical and experimental study is 8.6% and 10.8% respectively. The correction factors suggested for the numerical and experimental data reduces the average percentage error to 0.7% and 2.3% respectively. The repeatability tests show ±1.8% uncertainty in the flowrate. Integrating velocity along the acoustic path can roughly estimate measurement uncertainty due to flow profile without simulating the ultrasonic wave propagation numerically. This research will help increase the use of clamp-on ultrasonic flowmeters in practical applications with reduced uncertainty.

Summary for Lay Audience

Various different types of flowmeters are used to measure the flowrate of a liquid inside a pipe but this thesis focuses on a clamp-on ultrasonic liquid flowmeter. A clamp-on ultrasonic flowmeter sends and receives ultrasonic signals between its two transducers which are clamped on the outer side of a pipe. The ultrasonic signal that propagates in the direction of the fluid flow travels faster when compared to the ultrasonic signal that travels in the opposite direction of the fluid flow. The time difference between the two signals and the time taken by the individual signals to propagate inside the fluid is used to estimate the fluid velocity and volume flowrate. The disturbance in the fluid flow profile due to pipe bends causes an error in the readings of these flowmeters. In this thesis, a 3D numerical approach to model the working of a clamp-on ultrasonic flowmeter in the presence of a fluid flow inside a straight pipe and downstream of a 900 elbow is proposed. An experimental study is also conducted to investigate the performance of an existing clamp-on ultrasonic flowmeter in both conditions. A percentage error due to the distorted fluid flow profile at the downstream of an elbow is observed in the numerical and experimental study. Correction factors are proposed which could be applied to such flowmeters installed in similar flow conditions to reduce the uncertainty in the measurement. This study contributes towards further development in the existing clamp-on ultrasonic flowmeters and will also help in the use of these flowmeters in practical applications with greater accuracy.

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