Discrete axial motion of a radioactive tracer reconstructed from the response of axially aligned detectors:Application to the analysis of a bubble column dynamics

The feasibility of extracting relevant dynamic information of a bubble column from the approximate reconstruction of a radioactive tracer axial trajectory using a set of axially aligned detectors (AAD) is explored. The experimental procedure involves scanning simultaneously different column heights with scintillation detectors, located vertically aligned beside the examined vessel, while a neutrally buoyant radioactive tracer particle is freely moving inside. The reconstruction considers that the detectors located closer in axial coordinate to the tracer are the ones which record the largest number of counts. Based on this assumption, time series of the approximate tracer axial coordinate are obtained with a maximum resolution of 2. N-1 (N: number of detectors used). Compared to the powerful radioactive particle tracking (RPT) technique, although the information extracted is more limited, the present experimental procedure has the advantage of not requiring a calibration stage, which is rather cumbersome to implement at industrial scale and prevents RPT massive use for troubleshooting. Part of the information extracted from the analysis of tracer axial trajectories in RPT can also be inferred from the discrete tracer axial trajectories obtained with this methodology. Therefore, tracer fast axial velocity distributions, liquid axial mixing time and liquid holdup axial profiles are estimated from the reconstructed axial trajectories and related to the operating conditions, for experiments with water and non-Newtonian aqueous solutions of carboxymethyl cellulose (CMC). © 2013 Elsevier Ltd.