Gas-solid Two Phase PDF Model And Numerical Simulation Of Oil-less Ignition System

In recent years, the PDF approach has evolved as rigorous mathematical tool for the description of two-phase flows. One of key problems of the approach is how to derive a reasonable PDF transport equation from the particle Langevin equations in two-phase flows. In this paper, using the method of state vector expanding color-noise system for color-noise system, the joint PDF equation of particle position-particle velocity-fluid velocity is gained, and the PDF equation of particle position- velocity is also obtained by reducing the state vector of system. On the assumption of Gaussian process, the PDF equation is closed using the method of Gaussian integration by part, and then the second-order moment model of two-phase flow is obtained. A numerical method named "finite analytic/Monte-Carlo" is developed. A wall-jet-flow loaded with solid particles is calculated using the "finite analytic/Monte-Carlo" numerical method, the numerical results are analyzed and compared with the experimental results.On the other hand, whole combustion process of a two-stage oil-less ignition system is simulated detailedly, especially numerical simulation for the two-phase flow of the system is carried out using the PDF model discussed above. Detailed analysis is conducted on the velocity field, the pulverized coal concentration and temperature, and the results indicate that: in the first stage of the two-stage oil-less ignition system, the flow characteristics and the distribution of pulverized coal concentration make for the ignition of pulverized coal by heating pipe, and during procedure of ignition there are three different kinds of temperature distribution on the cross sections of heating pipe; the flow characteristics in the second stage makes for the mixing of gas phase, and the flame temperature is higher in the second stage. Then the simulation results are compared with the experiment results. And it is believed that the results can be helpful to operation and optimizing design of two-stage oil-less ignition system.