The Study And Application Of Kinetic Monte Carlo Method In Multiscale Simulation

Advanced energy system has the highly complex and multi-scale features, and requires a very high efficiency and near zero emissions. In general, the mathematical description of the continuity which applied on macro-phenomena has some limitations in the microscopic scale; on the other hand, the price is too high to use domain rules, such as the kinetic Monte Carlo(kMC),Lattice Boltzmann(LB) or molecular dynamics (MD) calculation in all the macro-scales. Therefore, dividing the scale of system rationally and using effective simulation algorithm respectively can effectively solve the two major bottlenecks——calculating costs and organizational complexity,which exists in the complex system. In most cases, advanced energy systems involve various types of chemical reactions in the process of achieving energy conversion and controlling environmental, for the micro-scale simulation of reaction-diffusion process, kMC is a moderate computational and efficient algorithm. Starting form the micro scale, kMC simulates the movement of particles by using a random way, which reflects the macro changes by describing the volume change of the particles. It provides important data for the macro-scale simulation.This paper studies the mechanism of kinetic Monte Carlo (kMC) simulation method which based on the microscopic simulation technology, and then focuses on a specific implementing way of kMC——Gillespie stochastic simulation algorithm. Taking the solid oxide fuel cell (SOFC) as the study object, first uses Gillespie algorithm to simulate the electrochemical reaction process, then starts from the SOFC micro-scale, author simulates diffusion process of oxygen vacancies in the electrolyte of yttria stabilized zirconia (YSZ) with the kMC simulation method. The application of kMC on the SOFC is the focus of this paper, which includes the following aspects:1. Studies the Gillespie stochastic simulation algorithms of the kMC micro-simulation method, and tracks the variation of the substances'molecule numbers in the electrochemical reaction of SOFC to reflect the dynamic characteristics of the electrochemical reaction by this method.2. One-dimensional kMC lattice model is established along the direction of the electrolyte thickness, and the step time and the events of the oxygen vacancy hopping in the lattice are determined by the random number, and then tracks the number of oxygen vacancies on each lattice. The system status is updated all the time. In addition, this paper focuses on an analysis of the effect of temperature,the initial structure of the distribution in electrolyte and the frequency of voltage applied on the electrode on current density,Ve Nlec(the potential at the Nth layer lattice produced by the positive charge and the electronic aggregation in electrodes ),Vt oNtal(the total voltage at the Nth layer lattice) and the distribution of oxygen vacancies. The results have the characteristics of probability and statistics, which describe the dynamic characteristics of the system accurately.This paper attempts to simulate the micro-process of the energy systems with kMC preliminary, and takes the SOFC as the object, studies the electrochemical reaction and the diffusion process in the electrolyte of oxygen vacancies. The simulation results show that, the dynamic characteristics of the system can be revealed by describing the small unit and their interaction of the system, and the macroscopic parameters can be reflected by the microscopic description, which achieved a leap in scale.