Droplet phase change model and its application in wave-type vanes of steam generator

When an entrained droplet travels through the steam-water separator of the steam generator in a nuclear power station, pressure decreases continuously along the droplet trajectories due to the local flow resistance and structure variation. This movement-induced pressure drop will result in droplet evaporation, which eventually affects the steam-water separation performance. To investigate the influence of the droplet motion on its phase change, a phase change model for single moving droplet is developed by combining static droplet phase change model and droplet motion model. The model well reproduces the droplet evaporation process, showing a fast evaporating stage followed by a thermal equilibrium evaporation stage. The discrepancies between the predicted results and the experimental measurements are within ±2%. Furthermore, the model is adopted in the Euler-Lagrange frame to obtain the phase change characteristics of droplets moving in the wave-type vanes. Based on the simulation, the effects of phase change on the droplet movement trajectory, radius, velocity, terminal position and separation efficiency are examined. In addition, the critical pressure difference that could affect the wave-type vanes separation efficiency about 0.01 % is proposed. The theoretical and numerical work can provide guidance to the design and optimization of the steam-water separating apparatuses as well as other applications where both of the droplet movement and phase change occur simultaneously.