Visualization of local two-phase flow structure in a packed bed of spheres

Abstract

A two-phase flow structure in porous media is essential to clarify the debris cooling characteristics during a severe accident in nuclear power plants. In previous experimental studies, a packed bed of spheres has been used instead of the porous debris bed. Many models to predict the flow and heat transfer characteristics in the packed bed have been proposed based on the experimental data in the sphere-packed bed. However, those models have not considered the local flow structure, which should be studied to enhance the prediction accuracy. In this study, the local flow structure of the air-water two-phase flow in the unit model of the sphere-packed bed was measured by neutron computed tomography. The distribution of the gas phase was reconstructed by acquired images. From these results, the breakup and coalescence of the bubbles in the packed bed were evaluated.