Simulations on LN2–VN2 flooding phenomenon in inclined tubes using a modified AIAD model

Abstract

Simulations basing on the Eulerian multiphase model and a modified algebraic interface area density (AIAD) model are carried out to study the flooding mechanisms with liquid nitrogen (LN2) and its vapor (VN2) in an inclined pipe. The original AIAD model predicts well for the water-air flooding velocity, which assumes three flow patterns in the whole hydraulic process, including the free surface flow, bubbly flow and droplet flow. Much different flooding phenomenon for LN2-VN2 is experimentally observed by the present authors, which indicates that some parameters have to be modified for LN2-VN2 occasion. The flooding onset is mainly identified by the sharp increase of pressure drop in this paper. As expected, the modified AIAD model predicts LN2-VN2 flooding velocity with a higher accordance with experiment than before. Both the experiments and calculations show that the flooding process of LN2-VN2 goes through three stages from stratified flow to wavy flow, and finally to mist flow with the appearance of spray entrainment, which is different from the final slug flow in water-air cases. Influences of geometric factors, such as tube length and diameter, are also investigated in this research.