Investigation Of Fluid Flow And Micro-Particle Transport In A 3D Scaled-up Alveolar Model

In the past forty years,with the increasing air pollution caused by the rapid development of China's economy,various respiratory diseases have been induced.Respirable particulates in the air,especially PM2.5(into the lung particles),are inhaled into the lungs of the human body,and movement to the lung acinar area deposits can seriously damage the respiratory tissue.The alveoli are the smallest unit involved in gas exchange in the lungs.The transport of inhaled aerosol particles is mainly affected by the flow pattern in the alveoli and,ultimately,mainly on the alveolar wall.Therefore,studying the flow pattern of fluid in the alveoli is the first step in predicting the transport and deposition of aerosol particles in the human acinar region.Because of the sub-millimeter size and the inaccessibility of lung acinus,the flow characteristics in the alveoli are often difficult to analyze,so measurement of flow phenomena and particle transport remains a very challenging.At present,there are two main experimental approaches in this field.One is to construct a real model equivalent to the size of the alveoli by microchip.However,due to the small size and complex structure of the alveoli,the existing micro-nano manufacturing technology cannot fabricate the alveoli structures with the actual size.And the current main research content is limited to two-dimensional flow,and the three-dimensional flow data of the real model cannot be obtained.Therefore,some scholars complement the defects of the real model by establishing an alveolar scaled-up model,but the most current experiment of amplifying the model only performs geometric similarity and unmatched fluid dynamics.Moreover,it is impossible to accurately control the consistency of the alveolar expansion and contraction process and the flow input during the breathing process,it is impossible to reveal the details of the flow in the alveoli.At present,all the experiments of the magnified model only measure the data of a single plane,and we have not found three-dimensional quantitative flow data in the alveoli.In-depth study of three-dimensional flow data in the alveoli has important application value for exploring the hydrodynamics in the alveoli.This paper establishes a single in vitro three-dimensional alveolar amplification model with matching geometry and fluid dynamics similar,and synchronously controls of alveolar expansion and contraction and oscillating flow in th e alveolar duct to simulate real breathing conditions.Flow measurement technology was used to obtain representative(swirl flow and radial flow)flow field data in the three-dimensional magnified alveolar model,and saddle point phenomenon was observed in the flow recirculation region of each cross section in the alveoli.This complex flow behavior indicates saddle point phenomenon may be an important mechanism for chaotic mixing in the alveoli.The flow pattern in the alveoli is measured by a particle ima ge velocimeter(PIV),and a detailed vector diagram of the discrete points in a given period shows the flow field changes.The time-varying velocity vector field is integrated over multiple cycles to simulate the migration of particles in the alveolar spac e and deposition on the alveolar walls.It is found that the particles entering the eighth stage alveoli will be mainly deposited in the exit area,however,the particles entering the sixth stage are not completely deposited,and alveolar region are divided into "escape zones" and deposition zones,which provides an intuitive understanding for subsequent in-depth research in different regions.