On the relationship between pipe accelerance and the void fraction of internal two-phase flow

This work presents an experimental study on the forced vibration response of horizontal tubes subjected to internal gas-liquid two-phase flow. Vertical and horizontal polarizations of the flexural tube conveying mixtures of air and water are investigated. Firstly, the accelerance frequency response functions FRFv and FRFh, which represent the relationship between the acceleration in the vertical and horizontal axes and the corresponding forces measured in these directions, respectively, were obtained from different two-phase flow conditions in a wide frequency range (1-1600 Hz). Significant changes in the accelerance FRF's occur with void fraction. As expected, it was observed the increase in the natural frequencies of pipe and the increase of magnitude of the FRF's as a result of the reduction of the mass of liquid added to the tube with increasing void fraction of two-phase flow. The differences between the FRFv and the FRFh due to the asymmetry of the horizontal two-phase flow are investigated. Finally, the horizontal tube is harmonically excited at specific frequencies determined from the FRF's. Relationships between the pipe accelerance and the volumetric quality, as well as the relationships between the pipe accelerance and the void fraction of two-phase flow are obtained in the vertical and horizontal directions for different excitation frequencies. The results show that the pipe accelerance measured in the vertical and horizontal directions can be used to determine the void fraction and the volumetric quality of two-phase flow.