Characteristics of the local bubble parameters of a subcooled boiling flow in an annulus

An experimental study on the subcooled boiling phenomena was carried out in the SUBO (SUbcooled BOiling) test facility under steam-water flow condition. The test section is a vertical annulus of which axial length is 4.165 m with a heater rod at the center of a channel. The inner and outer diameters of the test section and the heater rod are 35.5 mm and 9.98 mm, respectively. For the measurement of the local bubble parameters, double sensor optical fiber probes were applied at six elevations along the test channel. Among them, one is installed in the unheated region which is located downstream of the heated section for the measurement of bubble condensation. A total of six test cases was chosen for the parametric study of the heat flux of 370–563 kW/m2, mass flux of 1110–2100 kg/(m2 s) and inlet subcooling of 19–31 K at pressure condition of 0.15–0.2 MPa. From the test, local void fraction, interfacial area concentration, Sauter mean diameter and bubble velocity were measured at 11 radial locations at each elevation. The measured data shows well development and propagation of the bubble parameters along the test channel. The present data is expected to be suitable for a benchmark, validation and model development of the CFD codes or existing safety analysis codes.