Gas-liquid two-phase flow in double tube annular passage with flow obstruction, (1)

In the steam-water two-phase flow in vertical multi-tube type steam generators, the presence of tube-supporting plates or spacers affects the flow remarkably, and it is feared that water film is apt to break around their fixing positions. It was clarified experimentally that the formation and disappearance of dry patches repeated on the surface of a heating tube were apt to occur in the limited position near an obstacle in boiling flow. Prior to this experiment, the change of water film thickness in course of time before and after an obstacle in air-water two-phase flow in a single tube, especially the relation between the mechanism of forming minimum water film thickness and the flow pattern, and the effects of the dimensions and shapes of the obstacle were examined. In the present study, the experiment on the air-water two-phase flow passing through the annular channel of a double walled tube was carried out, and the effects of obstacles similar to those described above were examined. The experimental setup and experimental method, and the results are described. The minimum thickness of water film occurred differently owing to the apparent flow velocity of air. When the flow rate of air was small, an annular obstacle caused drainage on the external surface, and water film became very thin on the upstream side. In the case of a spacer, it functioned only as the resistance to flow. (Kako, I.)