Influence of Viscosity, Density and Surface Tension on Two-Phase Damping

Internal two-phase flow is common in piping systems. Such flow may induce vibration that can lead to premature fatigue or wear of pipes. In the nuclear industry in particular, failure of piping components is critical and must be avoided. Two-phase damping is considered part of the solution, since it constitutes a dominant component of the total damping in piping with internal flow. However, the energy dissipation mechanisms in two-phase flow are yet to be fully understood. The purpose of this paper is to explore the relationships between two-phase damping and fluid properties. Simple experiments were carried out in a clear vertical clamped-clamped tube to verify the effects of fluid properties on two-phase damping. Various fluids, such as air, alcohol, pure water, sugared water, glycerol, and perfluorocarbon, were combined to obtain different controlled mixtures and to determine the effect of surface tension, density and viscosity on two-phase damping. Two-phase damping ratios were obtained from free transverse vibration measurements on the tube. Two sets of experiments with stagnant and moving continuous phase were conducted. Based on dimensional analysis, we obtained a semi-empirical model for two-phase damping in bubbly and slug flow. The Void fraction and Bond number are shown to be major parameters of two-phase damping, which is described as a kinetic energy transfer from the tube to the continuous phase through added mass of the dispersed phase.