Investigation of surface structures in two phase wavy pipe flow by utilizing X-ray tomography

The aim of this study is to investigate surface structures in two phase horizontal pipe flow. The flow regimes investigated vary from linear wavy flow to violent breaking wave regimes. Experiments are conducted in a 31 m long pipe with a diameter of 0.1 m. High temporally and spatially resolved X-ray measurements and conductance wave probe measurements are conducted simultaneously. The average phase speed measured by the conductance probes coincided with semi-theoretical linear wave theory for the cases where the surface was symmetrical about the centerline, and the superficial gas velocity Usg was kept below 2 m/s. The wave regimes, where asymmetrical surface structures were obtained, had an average phase speed that was lower than the semi theoretical prediction. This implies that asymmetry slows down the waves. In addition, the power spectral density (PSD) for the linear cases had distinct peaks, while for the other cases no peaks were obtained, and no preferred wavelengths were associate with the energy distribution for the nonlinear cases. The spectrum calculated from the X-ray images revealed that the second peak in the power density spectrum for the linear waves were not present at positions close to the pipe wall. The energy was instead distributed to other wave frequencies, which indicate that the waves were less regular close the pipe walls, and that the regions near the pipe wall are prone to extreme waves and breaking events. The irregularity close to the pipe walls and the broad energy distribution for the case with high gas velocity, are related to a one sided breaking event obtained on the left side of the pipe.