The inception, growth and collapse of vapor bubbles were observed and measured by using visual method under subcooled flow nucleation. The test section was a single-side heated rectangular channel by the scale of 2×40×700mm and the working fluid was clean water. The working condition was set as: the inlet subcooling Δ Tin = 330 °C, the mass flux m = 694kg/(m2s), the heat flux q = 210kW/m2 and the absolute pressure p = 0.22MPa. A high speed camera was used to record the bubble behaviors at the speed of 5000fps (frame per second). The results showed that the bubble lifetime was from 0.4ms to 2.2ms and the fraction of bubble with short lifetime was bigger than that of long lifetime. The bubble’s average diameter showed a linear relationship with the lifetime and it was also found that the sliding bubble would enhance heat transfer.

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