Analytical Study on Characteristics of Falling Water Limitation in Countercurrent Two-Phase Flow in Vertical Annular Channels.

Abstract

This study shows quantitatively that existing experimental data on countercurrent flow limitation (CCFL) or flooding in vertical annular channels can be predicted well by applying a criterion that the CCFL condition be given by maximizing falling water mass velocity with respect to falling water film thickness for the entire flow channel, which is the same criterion as that which the author successfully applied to the CCFL conditions for both vertical circular tubes and vertical rectangular channels. Quantitative analyses were carried out for the previous experiments of both air-water and steam-water countercurrent flow systems under atmospheric pressure in the vertical annular channels of 0.46 to 1.22m in length, 0.91 to 1.85m in circumference and 12.7 to 50.8mm in gap size in both cases where water is injected into the upper plenum and through nozzles, simulating a vertical channel in PWR pressure vessel.