Simulation Study Of The Deposition Of Submicron/Micron Particles In The Human Respiratory Tract

With the sudden global outbreak of COVID-19,virus aerosol spreads in the air and causes infection by human inhalation,so the problem of fine particle transmission and deposition in the respiratory tract has attracted a lot of attention from researchers.The study of flow field changes in the respiratory tract,as well as momentum and mass transfer between the flow field and particles,can have a positive effect on changing the deposition rate or distribution of particles in the respiratory tract.The rapid development of computer technology and computational fluid dynamics has given numerical simulations the advantage of comprehensive and rapid data acquisition and flexibility in changing conditions in the direction of particle deposition in the respiratory tract.In this paper,a numerical model of the movement and deposition of particles in the respiratory tract was constructed,the influence of various factors on the respiratory flow field,particle deposition rate and sediment distribution were studied,and a condensation growth model was constructed to study the enhanced deposition of condensation-enhanced deposition.The main research results are as follows:(1)A geometric model of the nasal cavity was reconstructed using CT images,and a numerical model of nasal particle motion was constructed by selecting a 1.27 million polyhedral mesh,an SST k-ω turbulence model with a discrete-phase calculation model and a 0.001 s time step to calculate the relationship between deposition rate and particle density at two different respiratory intensities and compare it with the physical experimental data.The results show that the CFD simulated values at low respiratory intensities are within ±20 % error from the experimental data,but at high respiratory intensities the model overestimates the deposition rate of small particle size,but the overall error does not exceed ±30 %;the effect of polydispersed particle size on deposition is also discussed,and it is concluded that the presence of polydispersity slows down the deposition rate curve significantly.(2)The important factors influencing particle deposition were identified through factorial experiment and then their effects on deposition were explored by response surface methodology,and then the pattern of particle deposition in the nasal cavity of patients was analyzed.The results show that the effect of particle size on deposition is the greatest during steady breathing,which is 4.96 times the intensity of breathing,and the quadratic term between them is not negligible,mainly because particle deposition is more influenced by inertia;during cyclic breathing,the effect of breathing conditions on deposition is mainly compared,and the effect of breathing frequency and breathing ratio on deposition rate is similar under the condition of fixed tidal volume,which is more than 30 times the breath-holding time The effect of the secondary term on deposition is similar to that of breath-holding time.Numerical CFD simulations of the nasal cavity of patients with hypertrophic rhinitis show that the deposition rate of the inferior turbinate decreases abruptly when the particle size increases above 7 μm,mainly because the larger particles are deposited more in the anterior turbinate but not deeper into the nasal cavity,and the increase in the deposition rate of the inferior turbinate does not exceed 1.1 %.(3)A geometric model of the respiratory tract from the nasal cavity to the fifth-generation bronchi was constructed using multiscale modeling in conjunction with a computational model of water vapor in air condensing on aerosols when cold,and condensation-enhanced growth as a way to enhance lung deposition was investigated.The results show that,although not as strong as the direct large increase in particle size for enhancing lung deposition,the enhancement of deposition by condensation growth can reach 64.6 % for small particle size and 9.52 % reduction in exhaled waste during exhalation.Choosing a small particle size combined with condensation growth technology can not only increase lung deposition,but also does not greatly increase the deposition rate of the nasal cavity,which is a good choice.