Computational case study on upward two-phase flow in vertical circular pipe based on CFD approach: Multidimensional flow instabilities investigation

In this paper, a numeric scheme made up of the three-dimensional (3-D) Two-Fluid Model (TFM) and the Rensselaer Polytechnic Institute (RPI) wall boiling model for two-phase flow instabilities simulation was validated by comparing its results with the flow boiling and instability experimental data. Then two-phase flow instabilities in a vertical circular channel were studied based on the validated numeric scheme. The flow instability was analyzed by both the Lumped Parameter Approach (LPA) and the Distributed Parameter Approach (DPA). The average parameter oscillation characteristics and local distributions were analyzed. The transient responses of the local conditions during the flow instability were discussed. Besides, the stability of the vertical circular tube channel flow boiling system was studied with the stable map based on the subcooling number (Nsub) versus the phase change number (Npch). This study provides a new feasible scheme for the simulation of flow instability which also actualizes an improved understanding of multidimensional flow and heat transfer characteristics in the flow instabilities phenomenon.