An asymptotic model of particle deposition at an airway bifurcation

A numerical simulation of the process of the outflow of gas under pressure into a closed container partially filled with liquid was carried out. For comparative theoretical analysis, an asymptotic model was used with assumptions about the adiabaticity of the gas outflow process and the ideality of the liquid during the oscillatory one-dimensional motion of the liquid column. In this case, the motion of the liquid column and the evolution of pressure in the gas are determined by the equation of dynamics and the balance of enthalpy. Numerical simulation was performed in the OpenFOAM package using the fluid volume method (VOF method) and the standard k-e turbulence model. The evolution of the fields of volumetric gas content, velocity, and pressure during the flow of gas from the high-pressure chamber into a closed channel filled with liquid in the presence of a ”gas blanket“ at the upper end of the channel is obtained. It was shown that the dynamics of pulsations in the gas cavity that occurs when the gas flows into the closed region substantially depends on the physical properties of the liquid in the volume, especially the density. Numerical modeling showed that the injection of gas into water occurs in the form of a jet outflow of gas, and for the outflow into liquid lead, a gas slug is formed at the bottom of the channel. Satisfactory agreement was obtained between the numerical calculation and the calculation according to the asymptotic model for pressure pulsations in a gas projectile in liquid lead. For water, the results of calculations using the asymptotic model give a significant difference from the results of numerical calculations. In all cases, the velocity of the medium obtained by numerical simulation and when using the asymptotic model differ by an order of magnitude or more.

Download Full-text

Near Wall Turbulence Effects on Particle Transport and Deposition in Human Tracheobronchial Multi-Level Bifurcation Model

Volume 2: Fora ◽

10.1115/ajkfluids2015-26336 ◽

2015 ◽

Author(s):

Amir A. Mofakham ◽

Lin Tian ◽

Goodarz Ahmadi

Keyword(s):

Boundary Conditions ◽

Particle Deposition ◽

Flow Simulation ◽

Tracheobronchial Tree ◽

Lung Model ◽

Wall Turbulence ◽

Nano Particles ◽

Turbulent Regime ◽

Computationally Efficient ◽

Multi Level

Transport and deposition of micro and nano-particles in the upper tracheobronchial tree were analyzed using a multi-level asymmetric lung bifurcation model. The multi-level lung model is flexible and computationally efficient by fusing sequence of individual bifurcations with proper boundary conditions. Trachea and the first two generations of the tracheobronchial airway were included in the analysis. In these regions, the airflow is in turbulent regime due to the disturbances induced by the laryngeal jet. Anisotropic Reynolds stress transport turbulence model (RSTM) was used for mean the flow simulation, together with the enhanced two-layer model boundary conditions. Particular attention is given to evaluate the importance of the “quadratic variation of the turbulent fluctuations perpendicular to the wall” on particle deposition in the upper tracheobroncial airways.

Download Full-text

A Numerical Study of the Effect of Particle Size on Particle Deposition on Turbine Vanes and Blades

Advances in Mechanical Engineering ◽

10.1177/16878140211017812 ◽

2021 ◽

Vol 13 (5) ◽

pp. 168781402110178

Author(s):

Zhengang Liu ◽

Weinan Diao ◽

Zhenxia Liu ◽

Fei Zhang

Keyword(s):

Particle Size ◽

Particle Deposition ◽

Numerical Study ◽

Stokes Number ◽

Capture Efficiency ◽

Particle Capture ◽

Factors Affecting ◽

Pressure Surface ◽

Deposition Area ◽

Turbine Vanes

Particle deposition could decrease the aerodynamic performance and cooling efficiency of turbine vanes and blades. The particle motion in the flow and its temperature are two important factors affecting its deposition. The size of the particle influences both its motion and temperature. In this study, the motion of particles with the sizes from 1 to 20 μm in the first stage of a turbine are firstly numerically simulated with the steady method, then the particle deposition on the vanes and blades are numerically simulated with the unsteady method based on the critical viscosity model. It is discovered that the particle deposition on vanes mainly formed near the leading and trailing edge on the pressure surface, and the deposition area expands slowly to the whole pressure surface with the particle size increasing. For the particle deposition on blades, the deposition area moves from the entire pressure surface toward the tip with the particle size increasing due to the effect of rotation. For vanes, the particle capture efficiency increases with the particle size increasing since Stokes number and temperature of the particle both increase with its size. For blades, the particle capture efficiency increases firstly and then decreases with the particle size increasing.

Download Full-text

Numerical assessment of natural respiration and particles deposition in the computed tomography scan airway with a glomus tumour

Proceedings of the Institution of Mechanical Engineers Part E Journal of Process Mechanical Engineering ◽

10.1177/09544089211024063 ◽

2021 ◽

pp. 095440892110240

Author(s):

Digamber Singh

Keyword(s):

Computed Tomography ◽

Respiratory Tract ◽

Particle Deposition ◽

Flow Characteristics ◽

Glomus Tumour ◽

Computed Tomography Scan ◽

Human Respiratory Tract ◽

Airflow Pattern ◽

Human Airways ◽

Tomography Scan

The human respiratory tract has a complex airflow pattern. If any obstruction is present in the airways, it will change the airflow pattern and deposit particles inside the airways. This is the concern of breath quality (inspired air), and it is decreasing due to the unplanned production of material goods. This is a primary cause of respiratory illness (asthma, cancer, etc.). Therefore, it is important to identify the flow characteristics in the human airways and airways with a glomus tumour with particle deposition. A numerical diagnosis is presented with an asymmetric unsteady-state light breathing condition (10 l/min). An in vitro human respiratory tract model has been reconstructed using computed tomography scan techniques and an artificial glomus tumour developed 2 cm above a carina on the posterior wall of the trachea. The transient flow characteristics are numerically simulated with a realizable (low Reynolds number) k–ɛ turbulence model. The flow disturbance is captured around the tumour, which influenced the upstream and downstream of the flow. The flow velocity pattern, wall shear stress and probable area of inflammation (hotspot) due to suspended particle deposition are determined, which may assist doctors more effectively in aerosol therapy and prosthetics of human airways illness.

Download Full-text