The development of a novel combined "ultrasonic/thermal" with "ultrasonic multiple
reflections" clamp-on meter for measuring a wide flowrate range of clean liquids in
small diameter pipes is presented. Current existing flowmeters based on ultrasound
cannot measure very low flowrates for single phase liquids. The ultrasonic/thermal
technique can measure single phase flows in the range 0 to 0.6 m s' in pipes with
diameters as small as 15 mm. It can also detect and measure reverse flows. The
minimum flowrate for the ultrasonic multiple reflection technique is about 0.55 m s',
and theoretically, the measurement accuracy increases with increased flow velocity.
The ultrasonic/thermal technique is based on a heating element and transducer pair(s)
which can be clamped to the outside of a pipe. With the heaters switched on, the
changes in the temperature of the pipe and the liquid inside it result in changes in
transit time. The flowrate can be therefore estimated by either the transit time difference
across the pipe at the two symmetric locations with respect to the heater centre, or at
one location with a heater off/on comparison. The latter approach was felt to be the
promising for low flowrate measurements and therefore selected for the numerical and
the experimental investigations. The multiple reflection technique was developed based
on the conventional transit time flowmeter. This technique extended the measuring
range of the flowmeter and provided cross calibration for the ultrasonic/thermal
technique. A computer model was developed for the ultrasonic multiple reflection
technique. However, there was insufficient experimental data to confirm the computer
prediction.
Results from computational fluid dynamics (CFD) analysis of the meter are presented.
For vertical pipes an axisymmetric model was used, but the presence of buoyancy
forces required the use of a 3-D model for horizontal pipes. Temperature and velocity
distributions and ultrasonic transit times have been computed and are presented.
In order to overcome the problem of mode conversion and refraction at the pipe
wall/transducer mounting interface, novel transducers and mounting blocks are
presented. A prototype heater and ultrasonic transducer system together with electronics
for signal generation and transit time measurement have been designed and constructed.
A hydraulic system has also been designed and constructed for testing the developed
clamp-on flowmeter. Experimental results from this apparatus are presented and compared
with the CFD predictions, and a technique for compensating for variations in inlet
temperature is described. The full scale difference between the computed values and
experimental results of the meter for low flowrate measurement was about 3.5%.
| Identifer | oai:union.ndltd.org:CRANFIELD1/oai:dspace.lib.cranfield.ac.uk:1826/4596 |
| Date | 02 1900 |
| Creators | Law, Masa |
| Contributors | Sanderson, M. L., Guilbert, A. R., Ward, G. |
| Publisher | Cranfield University |
| Source Sets | CRANFIELD1 |
| Language | English |
| Detected Language | English |
| Type | Thesis or dissertation, Doctoral, PhD |
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