Dynamic evolution characteristics of bubble groups in microchannels for flow boiling with the inlet two-phase effect

Microchannel flow boiling is an efficient thermal management technology, where the dynamic behavior of bubble groups significantly impacts heat transfer performance. This experimental study investigates how the inlet two-phase effect modulates bubble behavior and heat transfer performance. High-speed imaging techniques were used to capture the dynamic behavior of bubbles under varying heat input ratios (HIR), focusing on the analysis of bubble equivalent diameter, centroid position, distribution, and their influence on heat transfer. The results show that the inlet two-phase effect enhances heat transfer performance, increasing the overall heat transfer coefficient by 2.13 times compared to single-phase inlet conditions at an inlet vapor quality of 0.09. Without the inlet two-phase effect, the centroid distribution of elongated bubbles is skewed, primarily concentrated in the mid-to-late sections of the microchannel. In contrast, the inlet two-phase effect leads to a more uniform bubble distribution, promoting the formation of elongated bubbles and enhancing the vapor-liquid interface expansion. As HIR increases, the equivalent diameter of the elongated bubbles also grows significantly. Such a phenomenon leads to changes in the centroid fluctuation patterns of the elongated bubbles, with the total bubble area expanding to at least twice that observed without the inlet two-phase effect. This expansion facilitates a more uniform temperature distribution, enhances heat transfer coefficients, and establishes a positive feedback mechanism.