Interfacial behavior of the air-water counter-current two-phase flow in a 1/30 scale-down of pressurized water reactor (PWR) hot leg

Abstract

The study on the interfacial phenomena of flooding during the counter-current flow of gas-liquid in a complex pipe was carried-out experimentally. It consists of a combination of the horizontal pipe, elbow and inclined pipes to simulate the hot leg pipe in a PWR. The inner diameter was 25.4 mm as scale down of real hot leg pipe of German Konvoi type reactor. The visual observations were performed using high-speed video cameras. The measured parameters were the liquid film thickness and the pressure difference between reactor pressure vessel (RPV) simulator and steam generator (SG) simulator. The film thickness inside the test pipe was determined by using the processed image of visual data.As a result, three different mechanisms at the onset of flooding in counter-current were clarified, and are strongly affected by liquid superficial velocity. At low liquid superficial velocity (JL), the flooding mechanism is triggered by the presence of wavy interface along the horizontal pipes in the form of a liquid blockage on the elbow. At the medium JL, the slug was detected along the horizontal pipe. However, the slug collapses immediately since the water is insufficient to maintain the blockage. At high JL, the slug occurs and travels along the horizontal pipe until the elbow. Moreover, the effect of the length of horizontal pipe on the interfacial behavior of air water counter current flow also can be explained. As the length of the horizontal pipe decreases, the onset of flooding occurs at a higher gas liquid mass flow rate.