What is the criteria in determining wether vibration may occur in a two phase flow system?...Let's say in terms of the volumetric percentage of liquid to vapor, what is the percentage in which piping vibration may occur? Also what is the minimum natural frequency that a piping system maybe designed to solve piping vibration such as two phase regime..Thanks all for your opinion...

There is no method available yet, you can use Energy Institute Guidelined for flow induced vibrations.

You'd better use the Fluent software to do two phase flow analysis.

Dear Borzki,

The only way to predict or eliminate TWO-PHASE FLOW-INDUCED VIBRATION is, calculating acoustic and mechanical natural frequencies and making 10% - 20% seperation between them. BOS Fluids software from PAULIN, can be used to calculate acoustic natural frequency.

I think, more important problem in 2-phase flow is SLUG flow. Slug loads are proportional to (ρ)(A)(V^2), where (ρ) is the density of the slug liquid, (A) is the inside area of the pipe cross-section and (V) is the velocity of the moving slug. Slug loads typically move through a piping system like waterhammer and steamhammer loads but do not reflect from end boundary conditions. Slug loading on an individual elbow, therefore, is generally only a single application load that can be readily treated in CAESAR II dynamic or static analysis by the application of a Dynamic Load Factor, usually equal to two.

The CAESAR II slug impact model uses a linear ramp-up of the impact load at each bend, where the total duration of the ramp is equal to (π/2)(R+r)/V, with R = bend radius, r = pipe radius, V = slug velocity. The maximum amplitude of the impact is assumed to be caused by momentum change and is ρAV^2.