Bubble departure size in forced convective subcooled boiling flow under static and heaving conditions

A visual study of bubble departure size in forced convective subcooled boiling flow under static and heaving conditions was presented. High-speed digital images of flow boiling phenomena were obtained, which were used to measure bubble departure diameter. Experiments were conducted at atmosphere pressure in a narrow rectangular channel, with mass flux ranging from 300 to 710 kg/m2 s, heat flux ranging from 65 to 298 kW/m2 and inlet subcooling ranging from 20 to 40 K. The heaving frequency, which is generated by a six degrees-of-freedom platform, ranged from 0.2 to 0.61 Hz. The results indicated that decreasing mass flux and increasing heat flux had a tendency to increase bubble departure diameter under static condition. In heaving motion, bubble departure size was affected by additional heaving acceleration and flow rate fluctuation. A bubble departure model was proposed to predict the bubble departure diameter under static and heaving conditions by considering the additional acceleration and flow rate fluctuation. The proposed model agreed well with the experimental data within the averaged relative deviation of ±17.5%.

► Experiment was carried out on bubble departure size under heaving motion.
► High-speed camera was mounted on heaving platform to capture bubble departure size.
► Trends of mass flux and inlet subcooling on bubble departure size were studied.
► Flow rate fluctuation and acceleration variation affected bubble departure size.
► A modified model was proposed to predict bubble departure size in heaving conditions.