Characteristics of bubble departure frequency in a low-pressure subcooled boiling flow

In order to measure the bubble departure frequency, a flow visualization system was set up on a vertical annulus test section with a heater rod by using a high-speed camera. In this study, we developed an efficient methodology of image processing for obtaining the bubble departure frequency data. Bubble nucleation was investigated under various thermal hydraulic conditions of water, which correspond to pressures from 167 to 346 kPa, mass fluxes from 214 to 1869 kg/m²s, heat fluxes from 61 to 238 kW/m², and subcooling degrees from 7.5 to 23.4 K. The characteristics of bubble departure frequency were analyzed with the present data. The measured data was compared with models available in existing literature and a more plausible model was proposed. © Atomic Energy Society of Japan.