Electromagnetic measurement of bubble velocity in two-phase dielectric fluid flow

This thesis deals with the theoretical and experimental investigation of two-phase flow for a dielectric liquid electromagneticf lowmeter. So far only limited investigationsi nto the possibleu se of electromagneticf lowmeters for multiphasef low measuremenht ave been made. These have been restricted to electromagnetic flowmeters designed for conducting water based (electrolytic) fluids. The possibility of designing electromagnetic flowmeters for use with insulating (dielectric) fluids such as oil and petrol has been existed for some years. However the measuremenot f two-phase flow of insulating fluids using electromagnetic flowmeters and the application of this knowledge to the measurement of the separate phases has not yet been a subject for research. An analytical model is developed which evaluates a transformer signal that is produced on the electrodes when a bubble unbalances eddy currents while it passes through the meter. The shape and magnitude of this signal for various positions in the pipe cross-section is investigated. The behaviour of this transformer signal for various electrode shapes is studied as well and it is found that when using large area electrodes the position of the amplitude along the pipe axis remains almost constant. For measuring the speed of bubbles passing through the meter a frequency analysis is carried out and shows that the peak frequency of the signal is proportional to the velocity of the bubbles. A flowmeter is built to carry out experimental work. The first sets of experiments are carried out with plastic beads fixed on a thin string which is attached around two wheels. The speed of the beads is adjusted by an electromotor which powered one wheel. In a second experimental design gas bubbles are injected in a vertical pipe which is filled with dielectric oil. Both types of experiments exhibit the behaviour predicted in theoretical analysis.