Design and optimisation of impedance probes for void fraction measurements

The performance of impedance probes for measuring the conductance of gas–liquid mixtures in horizontal pipes is here studied by means of the numerical solution of Laplace problem. In particular the work is aimed at optimising the probe geometry in order to improve the probe response both in terms of linearity and in terms of spatial resolution to step changes in phase distribution. Starting from basic shapes employed in literature (ring and half-ring electrodes), the adopted approach allowed new probe geometries (characterised by non-uniform electrode distance and/or electrode width) to be found. The analysis is performed with reference to annular, stratified and dispersed distributions and the results are compared with available theoretical models. Measurements have been carried out to verify the predicted sensor response and to ascertain the effect of the particle size on the probe response under dispersed flow conditions. The analysis demonstrates the behaviour of different probe arrangements with respect to different flow patterns and shows the possibility to obtain optimised geometries matching the desired features of linear response and of enhanced spatial resolution