Bubble departure size of multiple bubbles were investigated to explore bubble dynamic based on VOF visual simulation. By contrast, bubble departure size increased with the increasing of velocity from 0.2 m/s to 0.4 m/s and with the decreasing of subcooling degree from 10 K to 3 K. It was also found that there was little difference in bubble departure size corresponding to heat flux of 200 kw/m 2 , 300 kW/m 2 and 400 kW/m 2 , but the magnitude of heat flux increased the number of nucleation that contributed to the increasing of bubble size due to coalescence. Finally, a fitting correlation was proposed to predict bubble departure size based on important dimensionless numbers regarding velocity, heat flux and subcooling degree, and the prediction deviation is about 5%.

The numerical method was used to study bubble sliding characteristics and dynamics of R134a during subcooled flow boiling in a narrow gap. In the numerical method, the volume of fraction (VOF) model, level set method, Lee phase change model and the SST k − ω turbulent model were adopted for the construction of the subcooled flow boiling model. In order to explore bubble sliding dynamics during subcooled flow boiling, the bubble sliding model was introduced. The bubble velocity, bubble departure diameter, sliding distance and bubble sliding dynamics were investigated at 0.2 to 5 m/s inlet velocities. The simulation results showed that the bubble velocity at the flow direction was the most important contribution to bubble velocity. Additionally, the bubble velocity of 12 bubbles mostly oscillated with time during the sliding process at 0.2 to 0.6 m/s inlet velocities, while the bubble velocity increased during the sliding process due to the bubble having had a certain inertia at 2 to 5 m/s inlet velocities. It was also found that the average bubble velocity in flow direction accounted for about 80% of the mainstream velocities at 0.2 to 5 m/s. In the investigation of bubble sliding distance and departure diameter, it was concluded that the ratio of the maximum sliding distance to the minimum sliding distance was close to two at inlet velocities of 0.3 to 5 m/s. Moreover, with increasing inlet velocity, the average sliding distance increased significantly. The average bubble departure diameter obviously increased from 0.2 to 0.5 m/s inlet velocity and greatly reduced after 0.6 m/s. Finally, the investigations of the bubble sliding dynamics showed that the surface tension dominated the bubble sliding process at 0.2 to 0.6 m/s inlet velocities. However, the drag force dominated the bubble sliding process at 2 to 5 m/s inlet velocities.

Flow boiling in microchannel has become an effective solution for high-heat-flux cooling of electronic components and heat transfer equipment, research on flow boiling in microchannel benefits society. Visualization plays a key role in the research, flow patterns obtained by visualized tools contribute to the study of flow boiling in microchannels, it is embodied in the following two aspects: heat and mass transfer mechanism, flow pattern dynamics. Above two aspects are introduced and analysed so as to provide a reference for researchers who explore flow boiling in microchannels based on visualized flow patter.

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