Inertia and compressibility effects on density waves and Ledinegg phenomena in two-phase flow systems

The most common kind of static and dynamic two-phase flow instabilities namely Ledinegg and density wave oscillations are studied. A new model to study two-phase flow instabilities taking into account general parameters from real systems is proposed. The stability influence of external parameters such as the fluid inertia and the presence of compressible gases in the system is analyzed. High-order oscillation modes are found to be related with the fluid inertia of external piping. The occurrence of high-order modes in experimental works is analyzed with focus on the results presented in this work. Moreover, both inertia and compressibility are proven to have a high impact on the stability limits of the systems. The performed study is done by modeling the boiling channel using a one dimensional equilibrium model. An incompressible transient model describes the evolution of the flow and pressure in the non-heated regions and an ideal gas model is used to simulate the compressible volumes in the system. The use of wavelet decomposition analysis is proven to be an efficient tool in stability analysis of several frequencies oscillations.

► The stability influence of piping fluid inertia on two-phase instabilities is studied.
► Inlet inertia stabilizes the system while outlet inertia destabilizes it.
► High-order modes oscillations are found and analyzed.
► The effect of compressible volumes in the system is studied.
► Inlet compressibility destabilizes the system while outlet comp. stabilizes it.