Experimental investigation of local two-phase parameters in a 4 x 4 rod bundle channel under a subcooled boiling flow

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 x 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 degrees 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.