The effect of horizontal pipe length to the onset of flooding position on the air-water counter current two-phase flow in a 1/30 scale of pressurized water reactor (PWR)

An experiment for investigating the flooding phenomena in a complex system has been conducted. The test section consists of the ratio of horizontal pipe length and diameter (L/D): 25, 50 and 94.5 with the inner diameter of the pipe is 25.4 mm. The visual observation shows two flooding mechanisms: front-flooding and rear-flooding. Front-flooding was found to occur at the horizontal pipe with L/D = 50 and 94.5. Beside it is found also at horizontal pipe with L/D = 25, on low and medium superficial liquid velocity (JL*0.5< 0.32). This was initiated by the formation of a liquid slug that begins unstable waves on a hydraulic jump. While rear-flooding was found to occur at horizontal pipe with L/D = 25 at high superficial liquid velocity (JL*0.5 > 0.32). This was initiated by the sudden formation of a large wave that completely blocks the whole cross section of the pipe near the water outlet.