Flow regimes classification and spatio-temporal complexities in flashing flow

Two-phase flow is a nonlinear dissipative dynamical system which may exhibit phenomena that can be characterized as chaotic. Since the void fraction distribution represents the major factor in determination of flow rate, interruption and reestablishment of the two-phase natural circulation, we present a space-time description of flow regimes based on the bi-orthogonal decomposition of a spatio-temporal void fraction distribution into orthogonal temporal modes (chronos) and orthogonal spatial modes (topos). The global energy function is used to identify the space-time structures independently participating in the (kinetic) energy of the flow. The global entropy characterizes the full space and time structure of the signal and we use this quantity to obtain an objective indicator of different flow regimes appearing in two-phase natural circulation flow.