Boiling Heat Transfer and Flow Regimes in Microchannels—A Comprehensive Understanding

Flow boiling in microchannels has been investigated extensively over the past decade for electronics cooling applications; however, the implementation of microchannel heat sinks operating in the two-phase regime in practical applications has lagged due to the complexity of boiling phenomena at the microscale. This has led to difficulties in predicting the heat transfer rates that can be achieved as a function of the governing parameters. From extensive experimental work and analysis performed in recent years, a clear picture has emerged that promises to enable prediction of flow boiling heat transfer over a wide parameter space. Experiments have been conducted to determine the effects of important geometric parameters such as channel width, depth, and cross-sectional area, operating conditions such as mass flux, heat flux, and vapor quality, as well as fluid properties, on flow regimes, heat transfer coefficients, and pressure drops in microchannels. A detailed mapping of flow regimes occurring under different conditions has been facilitated with high-speed flow visualizations. In addition, quantitative criteria for the transition between macro- and microscale boiling behaviors have been identified. In this paper, these recent advances toward a comprehensive understanding of flow boiling in microchannels are summarized.