Author(s)

J. V. Madison

Abstract

Saturated two-phase fluid flows are often subject to pressure induced oscillations. Due to compressibility the vapour bubbles act as a spring with an asymmetric non-linear characteristic. The volume of the vapour bubbles increases or decreases differently if the pressure fluctuations are compressing or expanding; consequently, compressing pressure fluctuations in a two-phase pipe flow cause less displacement in the direction of the pipe flow than expanding pressure fluctuations. The displacement depends on the ratio of liquid to vapour, the ratio of pressure fluctuations over average pressure, on the exciting frequency of the pressure fluctuations and the damping factor. In addition, pressure fluctuations in saturated vapour bubbles cause condensation and evaporation within the bubbles and change periodically the liquid to vapour ratio and influence the dynamic parameters for the oscillation. The oscillations conform to an isenthalpic process at constant enthalpy with no heat transfer and no exchange of work. Due to friction forces the oscillations are subjected to quadratic fluid damping. The paper describes the governing non-linear equation for quadratically damped oscillations in saturated two-phase fluids with condensation and evaporation, and presents steady state approximate solutions for free and for pressure induced oscillations. Resonance criteria and stability are discussed. Keywords: two-phase flow, isenthalpic oscillations, quadratic fluid damping, saturated fluid, condensation, evaporation, steady state solutions. 1 Introduction A saturated two-phase fluid is a mixture of liquid and vapour. The volumetric ratio R between the vapour and the liquid portion is defined as

Keywords

two-phase flow, isenthalpic oscillations, quadratic fluid damping, saturated fluid, condensation, evaporation, steady state solutions.