Yuanzineng kexue jishu (Jul 2023)
Research on 2D Motion Model of Jet Droplet in Gravity Field
Abstract
Steam-water separation device has a very important role in various fields such as nuclear power, chemical industry, and the environment field. Among them, accurate and efficient simulation of gas-liquid two-phase flow is of great importance for the design of nuclear power steam generators, in which the liquid droplets generated mainly consist of small-sized film droplet and larger-sized jet droplet. The current experimental study is relatively macroscopic and it is difficult to obtain detailed information about the droplet motion, so numerical simulation method is needed to study the mechanism of droplet motion, the current two-phase flow simulation method mainly includes Euler-Euler method and Euler-Lagrange method, and the simulation accuracy of Euler-Euler method is relatively low. Although the Euler-Lagrange method has higher accuracy, its computational complexity increases significantly with the number of particles, and it is usually difficult to be used for large-scale droplet simulation. In combination with the Euler-Lagrange model of droplet motion, the Euler grid-approximation model describing the motion of small-sized film droplets has been developed, which can reduce the computational effort while maintaining accuracy. The model approximates the real particle motion as the motion of particles along the grid nodes, while the trajectory lines of droplets are modeled by the connecting lines between the nodes. In this paper, the physical mechanism explanation and mathematical expression of the Euler grid approximation model for large size jet droplet were given, and different densities were defined for the mesh nodes completely covered by the droplet and for the mesh node not completely covered by the edge of the droplet. The model was applied to the calculation of the lower gravity space of the actual AP1000 steam generator, and the velocity and density field of droplet including suspended droplet, droplet smaller than the suspended size and droplet larger than the suspended size under the steam flow field were obtained, where the jet droplet smaller than the critical size will move out of the calculation domain with force of the flow field, the jet droplet larger than the critical size will fall back to the free surface, and the droplet of the critical size will remain suspended at a certain location. The region with higher density is also obtained as the possible collision point. The model can be used to calculate the droplet separation efficiency of vapor separation device such as gravity separation space and guide the optimization design of separation device.
