(50e) Effect of Quadratic Fluid Damping in Two-Phase Liquefied Natural Gas

Two-phase LNG fluid flows are often subject to non-linear oscillations. Due to its compressibility the vapor bubbles act as a spring with an asymmetric non-linear characteristic. The volume of the vapor bubbles increases or decreases differently if the pressure fluctuations are compressing or expanding. Consequently compressing pressure fluctuations in two-phase liquid-vapor LNG cause less displacement than expanding pressure fluctuations. The displacement of the vapor bubbles is subject to quadratic fluid damping due to the viscosity of the LNG. The effect of the quadratic damping depends on the ratio of LNG liquid to vapor, the ratio of pressure fluctuations over average pressure and on the exciting frequency of the pressure fluctuations. The paper presents and discusses steady state solutions for free and pressure induced two-phase fluid oscillations with quadratic damping. Resonance criteria and damping effects of LNG two-phase flows on plant safety and operation are discussed.