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Subcooled boiling flow in a rod bundle geometry is an important phenomenon observed in the heat exchanger of heat transfer systems and reactor core of a nuclear power plant. However, experimental data on local two-phase flow parameters of rod bundle geometries in the subcooled boiling conditions are rare. In this study, an experiment was conducted to determine the distributions of the local two-phase parameters of a 4 × 4 rod bundle channel under a subcooled boiling water flow. The flow conditions were a mass flux range of 305 to 390 kg/m2s, a heat flux range of 190 to 274 kW/m2, and an inlet subcooling temperature of 20.5 to 25 °C at an inlet pressure of 200 kPa. The distributions of the void fraction, bubble velocity, interfacial area concentration (IAC), and Sauter mean diameter were measured with a four-sensor optical fiber probe (4S-OFP). The area-averaged bubble parameters were used to evaluate several drift-flux models and IAC correlations to assess their applicability to rod bundle channels. • Experimentally investigated subcooled boiling flow in a 4 × 4 rod bundle channel. • Local bubble parameters are acquired to Mass flux, heat flux, and inlet subcooling. • Area-average bubble parameters are obtained from local bubble parameter data. • Existing interfacial area concentration (IAC) and drift-flux models are evaluated. [ABSTRACT FROM AUTHOR]

• Local droplet parameters in a 2 × 2 rod bundle under annular-mist flow condition were measured using a double sensor OFP. • Droplet mass flux was obtained from the measured local droplet parameters. • The distribution and the trends of the local droplet parameters and the droplet mass flux were identified according to the change in the superficial gas and liquid velocities. • The effect of the liquid film on droplet mass flux was investigated. • New droplet entrainment and deposition models for annular flow in rod bundles were proposed. An experimental study was conducted to investigate the local droplet parameters for annular-mist air-water flow in a 2 × 2 rod bundle. It covered a flow condition of a superficial gas velocity (j g) range of 25–35 m/s (gas Reynold number (Re g) range of 39,132–54,785) and a superficial liquid velocity (j l) range of 0.015–0.040 m/s (liquid Reynold number (Re l) range of 432–1153) in an atmospheric pressure. From the test, the distributions of the local droplet parameters such as the droplet fraction, velocity, and diameter were measured by using a double sensor optical fiber probe (OFP). The effect of the superficial gas and liquid velocities on the local droplet parameters have been identified. Furthermore, the droplet mass flux over the measurement cross-section was obtained from the local droplet parameters distributions. It was found that the droplet mass flux has a decreasing trend with the superficial gas velocity and an increasing trend with superficial liquid velocity. That was attributed to the significant effect of the liquid film on the measured droplet mass flux and its trends. Moreover, the present droplet mass flux data were compared with the prediction of three existing droplet entrainment and deposition models. Finally, new entrainment and deposition rate models for predicting the droplet mass flux of a rod bundle were proposed and validated. The applicability of the proposed models is within the present experimental flow conditions range with a mean absolute percentage error (MAPE) of 10.34%. [ABSTRACT FROM AUTHOR]