Abstract: Since the mechanism of seed bubble triggering boiling flow heat transfer in microchannels could not be understood comprehensively, the volume of fluid(VOF) method is used to simulate the seed bubble triggering boiling flow in a circular microchannel under the high heat flux for four triggering frequencies. An accuracy and simple vapor-liquid phase change model is proposed to treat boiling flow process properly. Simulation results show that triggering frequency is one of the key parameters to control system heat transfer and stability. At low frequency(≤100 Hz), seed bubbles contribute least effects, and wall superheats vary with apparent millisecond-level fluctuation amplitudes. At high frequency(1 000 Hz or higher), with the frequency increasing, the fluctuation amplitude of wall temperatures can be successfully suppressed, the heating wall superheats attains the minimum degree. But triggering frequency can approach the saturation value(f = 2 000 Hz). In addition, the transient flow patterns and local heat transfer coefficient during the stable stage for saturated frequency are studied, continuous phase change heat transfer can be achieved, and the local heat transfer coefficient in the elongated bubble regimes can sustain 2-3 times the single liquid flow heat transfer.

Key words: Microchannel, Numerical simulation, Phase change, Triggered boiling