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Imaging of a distinctive large bubble in gas–water flow based on a size projection algorithm

Although electrical resistance tomography has been successfully applied to visualise gas–water two-phase flow in many applications, its capability for the determination of the sharp interfaces between gas bubbles and water is still below engineering expectations, which impedes effective estimation of fluid characteristics and flow regimes. A thresholding value method applied to a tomogram demonstrated a splendid view of most flow regimes, especially of a large bubble, but it may present a challenge with its accuracy in practice since the thresholding value was determined empirically. In this paper, a size projection algorithm is proposed for imaging a large bubble with a distinctive boundary, where the optimal thresholding value is automatically determined by minimising the projection error between measured voltages and computed voltages via a forward numerical solution, which specifically focuses on imaging of large bubbles. The accuracy of imaging a large bubble is evaluated by simulating the typical cross-sectional configurations of common pipeline flow regimes. Experimental results are reported in the paper, which were conducted on both horizontal and vertical pipelines engaged with typical gas–water flow regimes, including stratified, plug, slug and annular flow regimes. The results are also compared with the images obtained from a wire-mesh sensor system and high-speed camera videos recorded through a transparent photo-chamber lined in the test rig.