Measurement of Local Two-Phase Flow Parameters in an Annulus Under Low-Pressure Subcooled Boiling Condition

In this study, an experimental investigation is performed to measure the local bubble parameters in steam-water subcooled boiling flow under atmospheric pressure conditions. The test section is a vertical concentric annulus with an effective height of 2 m, and optical fiber probes are used to measure various local bubble parameters during boiling of the subcooled flow. The local void fraction, mean bubble velocity, interfacial area density, and Sauter mean diameter are measured at four elevations, and their radial profiles are obtained by traversing the tip of optical probes. In the experiments, the flow conditions were set for a heat flux of 370 kW/m2, a mass flux of 430~680 kg/m2s, and an inlet subcooling of 12~18 K at pressures ranging from 114 to 152 kPa.