Turbulent flow characteristics in an annulus under air bubble injection and subcooled flow boiling conditions

•Review of subcooled flow boiling experiments.•Air bubble injection and subcooled flow boiling experiments were performed.•Time averaged velocity profiles and fluctuations, and air bubble data are presented.•Velocity profiles for the boiling case were compared with a semi-empirical equation.

Air bubble injection and subcooled flow boiling experiments have been performed as part of the DOE Nuclear HUB project, Consortium for Advanced Simulation of Light Water Reactors (CASL). The main objective was to obtain a better understanding and detailed data needed to validate 3-D Interface Tracking Models and CFD models which can predict subcooled flow boiling phenomena in fuel assemblies of Pressurized Water Reactors. In both experiments, the flow channel was a vertical annulus of 4.8 mm gap width in which water at near atmospheric pressure flowed upward under a laminar or turbulent flow condition accompanied by air or vapor bubbles. The air bubble injection experiments yielded data on bubble formation and departure from a small hole on the inner tube, subsequent motion and deformation of the detached bubbles, and interactions with laminar or turbulent water flow. Instantaneous and ensemble-average liquid velocity profiles have been obtained using a Particle Image Velocimetry technique and a high speed video camera. Preliminary subcooled flow boiling experiments have been performed with subcooled water in the same annular channel geometry but with an electrically heated rod to generate the vapor bubbles. PIV measurements of turbulent velocity profiles in the presence of small vapor bubbles on the heated rod are presented.