Experimental study of two-phase parameters of subcooled boiling flow in a single-side heated rectangular channel

The rectangular channel is of particular interest for nuclear reactors due to its compact structure and high heat transfer efficiency. Two-phase flow characteristics in rectangular channels are different from those in conventional circular channels, which is important for the design and safety analysis of reactors. A subcooled boiling flow experiment was conducted using a single-side heated vertical rectangle channel at various system pressures of 0.80 MPa–1.80 MPa. Local two-phase parameters, namely void fraction, interfacial area concentration, bubble interfacial velocity, and bubble chord length, were measured by a double-sensor conductivity probe, and flow visualization images were captured by a high-speed camera. The bubble distribution feature of subcooled boiling flow in rectangular channels is revealed in this study. A “W” type distribution of void fraction was observed in cap-bubbly flow and the interfacial area concentration has a similar distribution as the void fraction, which illustrates that bubbles gather at the center and sides of the channel. Different from the adiabatic flow, the system pressure is a positive factor for the void fraction which is observed in this experiment. Furthermore, the accuracy of void fraction prediction models is assessed based on the experimental data. A large deviation is observed between the predictive and the experimental void fraction, which is related to the single-side heating feature of the flow channel.