Bubble Morphology Analysis and Pressure Drop of Gas–Liquid Two-Phase Flow inside a Quarto Static Mixer

The upward two-phase flow in vertical static mixers is beneficial for dispersion mixing. The bubble size distribution, aspect ratio, and angle distribution of the dispersed phase at various superficial liquid/gas velocities in an industrial Quarto static mixer (QSM) are experimentally studied. The dispersion performance of the QSM is assessed by Sauter mean diameter (d32), and the empirical correlation of axial d32 distribution is proposed. The gas–liquid pressure drop in the QSM is measured under UL = 0–0.071 and UG = 0–0.042 m/s, and two new dimensionless empirical correlations are proposed. Based on pressure fluctuation signal time series, the standard deviation, kurtosis, and skewness are analyzed, and the inlet and outlet critical velocities of flow pattern transition from pseudo-homogeneous to heterogeneous in the QSM are identified. Finally, the effect of UG on the dominant frequency and power spectral density function is quantitatively analyzed at the inlet and outlet sections.