| The characteristics of the particle deposition in the ventilation duct has great influence on the indoor air quality,subsequently affects the health of the indoor occupants.Therefore,investigating the deposition characteristics of particles in the ventilation ducts has a great significance for improving indoor air quality and ensuring people’s health.Besides,strengthening the deposition characteristics of particles in the ventilation ducts is a hot-spots of current research.At present,the research on the characteristics of particle in the duct is mainly through theoretical analysis,numerical simulation and experiment.In this paper,the numerical simulation method is used to study the deposition characteristics and mechanism of the fine particles in the ventilation duct with ribbed wall.Firstly,the current mainstream numerical simulation methods are summarized in this paper.In the ventilation duct,the gas flow is usually in a turbulent state,so the selection of a suitable flow model is essential to predict flow and particle deposition characteristics accurately.Therefore,three different flow models of standard 6)-,RNG 6)- and RSM are adopted in this paper to simulate the flow state and particle deposition in the ventilation duct,and the discrete phase model(DPM)is used to track the particles in the duct.The results show that all turbulence models can not accurately predict the pulsating velocity of the turbulent velocity in the near-wall region of the duct.So the velocity pulsation of the near-wall region must be corrected.In general,compared with the 6)- model,the RSM model can simulate the flow characteristics of the air better in the ventilation duct,the anisotropy is also considered,and the flow velocity pulse value can be predicted directly.The RSM model can accurately simulate the deposition process of the particles in the duct,and the simulation results are in good agreement with the literature data.Therefore,this paper uses RSM model and discrete random walk for subsequent research.Secondly,the influence of the additional inner and outer ribs on the deposition characteristics of the particles in the ventilation duct is studied in this paper.The results show that the addition of the inner and outer ribs in the ventilation duct can strengthen the deposition of the particles in the ventilation ducts,and the enhanced rate is higher when the inner ribs are added.For the small size particles,the maximum strengthening rate of the deposition velocity in the inner rib duct is 7771,and 1320 in the outer ribs.The increase of deposition velocity of the large size particle is rather small,only about 1~3 in the inner and outer rib duct.On the other hand,after adding the inner ribs,the pressure loss of the ventilation duct increases sharply,which is about 7.18 times of that of the smooth duct,and the pressure drop of the duct after adding the outer rib is only 1.08 times of the smooth duct.Considering both the enhanced rate and pressure loss of the particles in the ventilation duct,it is found that the deposition efficiency ratio of the ventilation duct with the outer ribs is slightly higher than that with the inner rib duct.Considering that adding the inner rib duct has a better effect on the strengthening deposition of the particles in the duct,the ventilation duct with different shapes of the inner rib is further studied in this paper.Finally,the influence of five different structures(front-trapezoid,rear-triangular,fronttrapezoidal,rear-trapezoidal,and square)rib added in the ventilation duct on the deposition characteristics of the particles is studied.It can be seen from the analysis,compared with the smooth duct,the addition of different structures of the ribs has a greater strengthening effect on the deposition of the small size particle,while the strengthening effect on the deposition of the large size particle is weaker.On the other hand,the pressure drop of the gas flow in the duct with ribbed is 6.7-8.8 times higher than that in the smooth duct.Therefore,the addition of the rib has no obvious enhancement to the deposition process of large size particle.Compared with the other four structures,the application of the fronttrapezoid ribs to the deposition process in the ventilation duct is greater than that of the other four structures.In short,the addition of a certain structure(such as the front-trapezoid)of the ribs on the surface of the ventilation ducts can enhance the deposition of the particles in the ventilation ducts,which is more pronounced for small size particles.Obviously,this provides a feasible way and method for removing fine particles from ventilated ducts. |
