Subcooling Effects for Flooding Experiments with Steam and Water in a Large Diameter Vertical Tube

A counter current annular flow experiment was performed to determine flooding conditions for varying degrees of subcooling using steam and water. The findings can be used in reactor safety codes to provide an improved model of flooding during accident analysis. The test section is a stainless steel tube which is approximately a 5/16 scale version of a pressurized water reactor (PWR) surge line. The water flows in an annular film down the inside of the tube and steam flows upward through the annulus. Flooding is the point at which the water film reverses direction and begins to travel upward. Flooding tests were conducted at atmospheric pressure for water flow rates between 3.5 gallons per minute (GPM) and 11 GPM and water inlet temperatures between 35 degrees C and 97 degrees C. The data obtained at high water subcooling indicate a significant departure from accepted flooding correlations developed for air-water systems which is expected because vapor condensation alters the steam inlet flow rate needed to induce flooding. The data more closely follow air-water data at low subcooling. Such data has not been seen in the literature for steam-water flooding experiments in a large diameter vertical tube and will serve as an important benchmark.