Browsing by Author "Guilbert, A. R."
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Item Open Access The Development and Modelling of a Novel Clamp-on Ultrasonic-Thermal and Ultrasonic Multiple Reflection Flowmeter for Liquid Applications.(Cranfield University, 1994-02) Law, Masa; Sanderson, M. L.; Guilbert, A. R.; Ward, G.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%.Item Open Access Modelling of piezoelectric ultrasonic transducers with application to high speed gas flow measurement(Cranfield University, 1991-07) Guilbert, A. R.; Sanderson, M. L.The design and testing of an ultrasonic time of ight Mach number probe for use in the bypass duct of an aircraft gas turbine is presented. Analysis of the time and frequency domain behaviour of the type of thickness mode transducers selected for use in the probe, and the effects of beam profile and attenuation on the transmitted ultrasonic wave in a owing medium are also covered and extended. The results of this analysis are implemented in a computer model which is used to aid in the design of various parts of the probe. Experimental assessment of the transducers designed for the probe is presented together with the results of tests on the performance of the selected probe configuration. A digital signal processing system to control the probe and compensate for the poor signal to noise ratio of the received signal is developed together with analogue circuitry to interface this system to the transducers. A novel method of compensating for the beam sweep encountered at the Mach numbers to b measured using 'ski-ramps' is then developed and implemented. Results from the final configuration including the ski-ramps is then presented.