Characteristics of average void fraction in vertical two-phase flow channels

The effective water head in the downcomer during the reflood phase in the postulated loss of coolant accident of PWRs, is dominated by the average void fraction in vertical two-phase flow channels. This report made clear the effects of physical properties of fluids, channel diameter and superficial velocities of two phases on the average void fraction in vertical flow system. As the results, the presentation of average void fraction by dimensionless groups can be obtained within errors of +- 15% in cases of steam-water and air-water flow systems under the stagnant liquid conditions including the case of very low liquid velocity (<30 cm/s). (author)