Motion And Collision Models Of Polydispersed Droplets

Moisture separator is an important equipment of steam generator of PWR nuclear power plant. Its main function is to eliminate the droplets from the humidity steam, for the dry steam can be supplied for the turbine to ensure the safety and economy of the nuclear power plantat operating state.The frequently happened flow regime in moisture separator is steam flow with droplets. Thus, it is siganificant to study the motion and collision laws of numerous droplets and establish the corresponding models for analyzing the mechanism of moisture separation, designing and optimizing the structure of moisture separator.Under Lagrangian-Eulerian methodology, this thesis proposed the motion and collision models of polydispersed droplets in moisture separator corresponding to numerical solving methods.Firstly, the variable of describing the motion behaviors of polydispersed droplets was analyzed according to the physical aspect. The motion model of polydispersed droplets and the numerical solving methods were established by building the relationships between Lagrangian and Eulerian variables. Then the model was verified by the free experimental data and calculation outcomes of comerical CFD software.Secondly, in order to develop routines for engineering computing, the solving methods of the motion model of polydispersed droplets were optimized from analyzingand improving the numerical stability of distretization schemes of the motion equation of characteristic droplet, applying k-d tree data structure to develop searching algorithm to increase executive speed of obtaining the flow information at the location of a droplet and develop droplet-locating algorithm to enhance the searching efficiency of locating the grid containing a droplet. What’s more, the working mechanism of moisture separators of AP1000(Advanced Passive 1000) nuclear power plant was studied in using the motion model of polydispersed droplets. And the results show that the separation ability to droplets of swirl-vanes placed in the primary swirl-vane separator is relative strong. The droplets are accumulated near the trepanning of inner sleeve, and the outer sleeve is full of droplets. Furthermore, the droplets moving in the gravity space can reach the state of kinetic equilibrium. The separation ability of bend hooks at the first and third stage of secondary chevron-type separator are more obvious than other hooks.Thirdly, the droplet collision algorithm based on collision kernel function was developed from understanding the physical process of droplet collision and drawing an analogy of the Monte Carlo method in simulating the neutron transportation. Based on other studies, the formulations of judging the collision regimes of binary-droplet and calculating the size, velocity and number of droplets after collision, were carried out to establishe the motion and collision model of polydispersed droplets. And the model was verified by the analytic solution, free experimental data and calculated outcomes of comerical CFD software. Finally, the motion and collision model of polydispersed droplets was used to perform the droplet distribution in a typical swirl-vane separator to study the working mechanism of the separator. Additionally, the motion behaviors of droplets were simulated by this model in AP1000 chevron-type separator. From changing the shape and number of bend hooks, another chevron-type separator with relative high separation efficiency and low pressure drop was carried out. In order to expanding the application area of this model, the transportation of spittle indoor was studied, and the distribution range of spittle under different ventilated state was performed.