Liquid Film Thickness in Vertical Circular Pipes Under Flooding Conditions at the Top End

• Published in: Nuclear technology 2020-03, Vol.206 (3), p.389-400
• Main Authors: Takaki, Toshiya, Murase, Michio, Nishida, Koji, Goda, Raito, Shimamura, Takeyuki, Tomiyama, Akio
• Format: Article
• Language: English
• Subjects: Countercurrent flow; flooding; liquid film thickness; square top end; vertical pipe
• ISSN: 0029-5450; 1943-7471
• DOI: 10.1080/00295450.2019.1656521

In our previous study, we measured the void fraction α, pressure gradient dP/dz, and countercurrent flow limitation in a vertical circular pipe (diameter D = 20 mm) under flooding conditions at the square top end and working fluids of air and water to obtain the wall friction factor f w and the interfacial friction factor f i based on the annular flow model. The thickness of the falling liquid film δ obtained from the measured α was relatively well expressed by the correlation for the free-falling film, and the obtained f w was well expressed by the Fanning friction factor f for a circular pipe. Measurements of α in vertical pipes under flooding conditions are few. In this study, therefore, we evaluated α and δ from the measured dP/dz under flooding at the square top end reported by Bharathan et al. with D = 50.8 mm and air-water and by Ilyukhin et al. with D = 20 mm and working fluids of steam and water at pressures of P = 0.6 to 4.1 MPa. As a result, we found that δ obtained from the measured dP/dz and the correlation of f w  = f were well correlated in terms of the liquid Reynolds number Re L . The obtained δ was well expressed by the Nusselt's correlation for the free-falling film in the region of laminar flows, but the obtained δ was larger than the Feind's correlation for the free-falling film in the region of turbulent flows due to the interfacial friction. We also discussed effects of the diameter and fluid properties on the interfacial friction factor f i .