Study on Fluid Flow States of Hanging Downcomer Bottom-Orifices

Abstract

Liquid in hanging or truncated downcomers flows downwards onto the lower tray through the downcomer bottom-orifices. At the bottom-orifices it is found that there exist three fluid flow states: liquid descending, vapor bubbling, and bridging. The mechanism of the three states was developed from the variation of the pressure acting on the bottom-orifices. The experiment was carried out in a 300 by 200 mm simulator with air-water system. Using a multi-path conductometer, the three states are successfully measured with an ingenious layout of conductometric probes. The results indicate that the ratios of bubbling and bridging increase with an increasing F-factor, and decrease with increasing liquid rate. Bridging really exists and is not negligible. The ratio of bridging is 0.4-1.8 of the ratio of vapor bubbling. Moreover, due to bridging, not only the bubbling vapor rate but also the ratio of bridging is restricted for the sealed hanging-downcomer.