An analytical model is proposed to study the two-phase flow instabilities of in-phase and out-of-phase modes in parallel boiling channels. This model takes into consideration the interaction between channels with different void fraction variations by modeling the diffusion of neutrons. Linear stability analysis in the frequency domain is performed to obtain stability boundaries and flow oscillation modes. In the case of parallel two channels, two types of stability boundaries are found to exist on the stability map; one for the instability of the in-phase mode and the other for that of the out-of-phase mode respectively. For a certain range of the void-reactivity coefficient, the void-reactivity feedback loop is found to be unstable in a certain region on the stability map, which has an effect on the stability of the in-phase mode. The interaction between channels affects the instability of the out-of-phase mode. The results are also obtained for the case of three and four channels. It is found that the channels having stronger interaction between them are more likely to oscillate in-phase with each other, while those having weaker interaction are more likely to oscillate out-of-phase with each other.

Issue Section:
Phase Change and Multiphase Heat Transfer
Keywords:
Computer Codes, Flow Instability, Multiphase Flows
Topics:
Boiling, Two-phase flow, Stability, Computers, Diffusion (Physics), Feedback, Flow (Dynamics), Flow instability, Modeling, Multiphase flow, Neutrons, Oscillations, Porosity
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