Characteristics of Two-Phase Flow in Packed Bed Systems

Two-phase pressure drop in the debris has been studied by many researchers in relation to the debris cooling characteristics during a severe accident in a nuclear reactor. However, its flow regime transition of the two-phase flow in the debris has not been well understood, which strongly affects the interfacial drag and the pressure drop. Conventional models for gas-liquid two-phase flow pressure drop have not been established well to evaluate interfacial drag accurately. In this study, high-speed imaging of a two-dimensional network model was performed to clarify the effect of flow pattern on interfacial drag and pressure drop. Normally it would be very difficult to visualize such two-phase flow behavior in an ordinary packed bed due to the reflection/refraction of light and/or overlapping bubbles, even if the test section is made of transparent materials. Therefore, in this study, a test section, which simulates two-dimensional network of porous structures, was fabricated to avoid the overlapping bubbles. By using a high-speed imaging of the two-dimensional network model, two-phase flow pattern in the porous structure have been identified. From the experimental results, it was suggested that the interfacial drag term should be modified in the gas-liquid two-phase flow pressure drop model.