Numerical Simulation Of Multiphase Pipe Flow

With the rapid industrialization, the demand for energy is much greater than ever before. However, the environment has been seriously damaged owing to the increasing consumption of the primary energy. New energy is gradually showing its advantages and importance, of which nuclear energy is the most environmental-friendly clean energy with the highest energy density. For the long-term development of nuclear energy, safety should come first.In the nuclear power system cooling circuit pipes, there are lots of erosion and corrosion products (particles) flowing with liquid flow, or depositing on the bottom of the pipes which forms bed with various heights (Bh). These beds often give rise to Prandtl Secondary Flow threatening the nuclear material integrity. This thesis simulated the single and multi-phase flow with three different bed heights (Bh=0,0.25,0.5), using Large-Eddy-Simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS). This kind of research with varying bed heights for non-circlar cross-section of pipe is very rare in the world, so this work is unique and the results obtained are valuable.This thesis found that the changed pipe boundary gave large boundary shear stress increasing the Reynolds stress gradients. Then the secondary flow formed and flow velocity and Reynolds stress increased with high Reynolds stress gradients. This phenomenon has great effect on the flow characteristics which dramatically influences the heat transfer. Multi-phase flow analysis found that small particles had the trend to flow with the liquid and the bigger ones (dp≥100μm) deposited more easily. Deposited particles form beds creating secondary flow which helps the particle do more effect on pipe wall and bottom in turn. These all post big threats to the nuclear material, causing material thinning and even accidents. Vigilant monitoring and detecting have significant importance for the nuclear safety.