A NUMERICAL SIMULATION OF TWO-PHASE FLOW INSTABILITIES IN A TRAPEZOIDAL MICROCHANNEL

Flow instabilities of convective two-phase boiling in a trapezoidal microchannel were investigated. using a three-dimensional numerical model. Parameters such as wall temperature and inlet pressure that characterize the instability phenomena of flow boiling with periodic flow patterns were studied at different channel wall heat fluxes and flow mass fluxes. Results were obtained for various wall heat flux levels and mass flow rates. The numerical results showed that large amplitude and short period oscillations for wall temperature and inlet pressure fluctuations are major characteristics of flow instability. The wall temperature fluctuations are mainly initiated by the transition from bubbly to slug flow patterns. Pressure fluctuations at the channel inlet and outlet were shown to be induced by the alternating flow patterns between bubbly and elongated slug flow. It was also noted that the amplitude and oscillation period of the inlet pressure fluctuations are strongly affected by the increased wall heat flux. Stable and unstable cases were identified by the different phase change numbers as the three cases invested all fit correctly in the flow boiling stability map.