Study on working mechanism of AP1000 moisture separator by numerical modeling

•PZB model is performed to simulate the droplet-laden flows in AP1000 moisture separator.•A theoretical way to analyze the numerical stability of PZB model is carried out.•A distinct algorithm to determine droplet location is introduced.•The working mechanism of all kinds of the moisture separators used in AP1000 is studied. AP1000 (Advanced Passive 1000) moisture separator that consists of primary, gravity and secondary separators is a crucial device to eliminate droplets from steam and supply dry-saturated steam to turbines. In order to understand the working mechanism of AP1000 moisture separator, droplet-laden flows are simulated in moisture separators based on the Lagrangian–Eulerian approach. In terms of details, the actual droplets are represented by parcels whose equations of motion are cast in a set of ordinary differential equations (ODEs), and the steam phase is described by Reynolds-Averaged Navier–Stokes (RANS) equations. Particularly, the numerical stability of solving the ODEs by using a fourth-order Runge–Kutta scheme is analyzed by a theoretical method in order to increase the time step size to save the computational time. Further, a distinct algorithm is introduced to rise the execution speed of locating a droplet in the grid by about 6000 times. The results show that, firstly, the separation efficiency of primary separator is beyond 90%. According to the moisture distribution on the x–z plane, the swirl-vanes placed in the inner barrel indeed play an important role to eliminate droplets. Secondly, the gravity space has no separation function, but it can make droplets follow the steam without speed disparity. Thirdly, the separation efficiency of the secondary separator is about 25%. This low value is attributed to the fact that only the hooks at the first and third stages can trap droplets.