Bubble parameters in an inclined rectangular channel with downward-facing heated wall under the subcooled boiling flow condition

Abstract

An experimental study was conducted to investigate bubble parameters in an inclined channel with a downward-facing heated wall. The flow conditions covered mass flux of 140–440 kg/m2s, inlet subcooling of 10–21 K, and heat flux of 50–142 kW/m2 at an inlet pressure of 110 kPa. From the test, the local bubble parameter distribution and bubble images were obtained from three measuring planes located along the flow direction using a four-sensor optical fiber probe and flow visualization techniques, respectively. It was found that the buoyancy-driven steam-water flow and re-wetting of the heated wall by the liquid phase had significant effects on bubble departure and lift-off. Additionally, the flow regime quickly developed from bubbly to slug flow owing to active bubble generation and coalescence at the heated wall. Furthermore, an interfacial area concentration correlation that can be applied to bubbly and slug flow regions was developed based on the existing modeling of the source/sink terms for the bubble number density transport equation. It predicted the experimental data within a mean absolute percentage error of 9%.