Nucleate boiling heat transfer is of significant interest for the design of a compact evaporator. This work investigates experimentally the nucleate boiling heat transfer in silicon based triangular and trapezoid microchannels with hydraulic diameter of 36.1 μm and 41.3 μm, respectively. Bubble nucleation and interactions are clearly observed in the entrance region, while the two-phase flow pattern in the microchannels is dominated by slug flow with long Taylor bubbles or annular flow. The evaporation of the very thin liquid film is speculated to be the major mode of heat transfer. The two-phase pressure drop is very significant and the corresponding variation in the saturation temperature should be considered in the analysis.

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