Visualization of sub-cooled flow boiling in hypervapotron cooling configuration

This work reports on experimental studies that examine the subcooled boiling on the enhanced heat transfer surface of the hypervapotron structure. The experiment was conducted for steady state, subcooled boiling with different heat fluxes (from 50 to 800 kW/m2). Working with a high speed (12,000 frames per second), high fidelity digital camera with variable magnifications (from 1x -25x), subcooled boiling in a single cavity was observed in detail. This research uses the simulant fluid Freon (R134A) instead of prototypic water to model the system performance. A major conclusion of this work is the existence of highly localized vapor production and motion characteristics. The process of bubble coalescence and vapor patch stagnation in the slot is believed to have crucial impact on local critical heat flux (CHF) performance. By approaching CHF conditions, the three wall sides of cavity show visible differences in the thermal behavior. The process of vapor bubble rotation in the cavity is believed to be helpful to enhance energy transfer, as evidenced by an improved wetting condition on the heating surfaces., However, this facilitation of rewetting appears to behave differently on the walls in a single cavity. (authors)