Horizontal slug flow characterization from non-intrusive piezoelectric pressure measurements

The characterization of slug flow is essential for the safety and efficiency of industrial processes, but traditional measurement techniques are often intrusive and difficult to implement in the field. This work proposes the use of non-intrusive piezoelectric pressure sensors to estimate key flow parameters, such as frequency, velocity, and characteristic lengths. Two sensor configurations were investigated in a horizontal water/air slug flow. The first uses Processed Pressure (PP) signals from axial sensors, while the second, and primary, one uses the Differential Pressure (DP) signal, calculated by subtracting the pressure measurements at the top and bottom positions of the pipe. The parameters were extracted using Power Spectral Density (PSD) and cross-correlation. The results were validated against reference data from resistive sensors and a high-speed camera. The investigation demonstrated that the DP signal accurately reflects the flow behavior, effectively serving as an indicator of the void fraction profile. The proposed DP-based methodology was statistically validated against reference sensors using Bland-Altman analysis. The results demonstrate that the methodology is statistically interchangeable with traditional techniques, as the mean biases for slug frequency, velocity, and unit cell length were consistently lower than the experimental uncertainties. While the Root Mean Square Relative Errors (RMSRE) were quantified at 11%, 25%, and 33%, respectively, the high degree of agreement confirms the robustness of piezoelectric sensors for non-intrusive flow characterization.