An image analysis technique for the study of gas–liquid slug flow along vertical pipes — associated uncertainty

An image analysis technique for the study of continuous co-current gas–liquid slug flow, in vertical columns, is reported. The technique comprises the automatic analysis of a sequence of video frames with the purpose of object (bubbles) tracking and characterization (dimension, velocity, distance). Its applicability to continuous slug flow conditions (even for very large number of bubbles) and the high accuracy of the results are the main added value of the proposed technique. The evaluation of the uncertainty associated with the parameters measured is performed (following the general uncertainty analysis approach). Partial uncertainties are acknowledged in bubble boundary definition, time measurement and calibration procedure. Expressions are derived for the computation of the overall uncertainty of bubble velocity, bubble length and liquid slug length. Global relative uncertainties of 5%, 2.5% and 7%, were found, for these parameters. The uncertainty estimation supports the ongoing trend for the implementation of image analysis techniques for the study of slug flow patterns.