Research On Indoor Fine Suspension Particle Model And Numerical Simulation Algorithm

In gas-particle two-phase flow, the large scale eddies play an important role in the diffusion process of particles. Due to the extremely low volume fraction whose order is about 10-10, particle diameters range from 0.003μm to 30μm typically. The main target of this paper is to find out the relationship between particles distribution concentration and gas flow.This paper is mainly to develop fine particle model and its numerical simulation algorithm based on the V2F turbulent model in Euler reference frame and Lagrangian reference frame respectively.The first chapter mainly reviews the published literatures and researches in the gas-particle flow field including study methods, multi-phase models for gas-particle flow, the numerical solution method and particle deposition model. In the end of the chapter, the outline of this dissertation is presented.The second chapter focuses attention on the application of the nonlinear turbulent mode,v2f model, in the flow in the air conditioning spaces. It is concluded that v2f model is more suitable for the simulation in such situations through the compare among several models simulation results and experimental data by other scholars. It is found that both in the forward zone and return flow zone or low supply velocity, The results using v2f model are much better agreement with the experimental data than other models does. The study showed that the validation of turbulence models and near-wall treatment methods is very important for obtaining reliable prediction results of ventilation flows.The third chapter mainly focuses the introduction of single phase models and deduces the fine particle model and its numerical simulation algorithm used in the following chapters. Basic on the law of mass conservation, the constitute equation for fine particle is advanced. In order to simulation the indoor fine suspension particles successfully, the effective turbulence viscosity of particle phase is handled separately in the turbulence core region and near-wall region (vicinities to walls). On the basis of deposition, the numerical condition of particle phase is presented. The model presented in this dissertation not only considered the influent variables including temperature, humidity, particle-particle collisions, coagulation. It can also predict the change of particle diameter under the situation when condensation and evaporation happened. The fourth chapter simulates the fine particle distribution and characters using different air distribution ways in the ventilation rooms including upper sidewall supply, both lower sidewall return, all ceiling air supply and both lower sidewall return, upper sidewall supply, and same lower sidewall return et al. air supply and return model.The fifth chapter compares the deposition rate results calculated by empirical equations and two different gradient diffusion models. It presents the deposition results under different supply velocity and different wall temperature conditions. Its main target is to see how the supply velocity and wall temperature influent the fine particle deposition rate.The sixth chapter pays attention to the fundamental problems using the stochastic particle trajectory model to predict the particle distribution. First of all, the chapter reviews the literatures and researches in the developing of stochastic particle trajectory model. For fine suspension particle, it mainly focuses on how to select the integral time step, and present an expression for the determinate of time step. The relationship between fluctuating frequency and integral precision is also discussed. It is found that higher gas fluctuating frequency will cause worse integral precision and to remain the same precision, the integral time step should decrease. In this chapter, the critic velocity whether the particle will rebound or not is deduced from the mechanism of particle-wall reaction. It is also concluded that the stochastic particle trajectory model is not the best way to simulation of indoor suspension fine particle due to the large quantity and its low volume fraction, especially when the recirculation eddy exist in the flow flied under nowadays computer condition. Though it is very expediently to see how the particles move and is beneficial to the assessment of indoor air quality, there are still exist such problem to be solved:1) How to select the fluctuating velocity while the fluctuating velocity divergence free? 2)how to consider the memory effect of the particle? 3) How to simulation the non-Markovian nature of the fluid velocity statistics along the solid particle trajectories?The seventh chapter draws general conclusions and presents perspective for future study.