An improved analytical solution on viscous dissipation effect in extended Stokes' second problem in microchannel with isothermal boundaries.

In this analytical study, the fluid motion within a microchannel is induced by the oscillation of one surface parallel to the other stationary surface, termed the extended Stokes' problem. The novelty and research gap are acquiring the thermal effect of such motion due to the viscous dissipation or fluid friction, subject to symmetric isothermal boundary conditions. The study may shed light on the role of viscous dissipation in temperature rise in the synovial fluid of an artificial hip joint, or in the fluid layer of a mechanical bearing. The full exact analytical temperature field, until now, has been unsolved, as it involves unsteady flow with manipulation of a complicated velocity field. The assumptions in the model are one-dimensional, incompressible, laminar, Newtonian flow with constant properties in a microchannel. Through the methodology of partial differential equation analysis, the temperature field is obtained in terms of Brinkman number, Prandtl number and a dimensionless angular frequency, and results are verified with a reported numerical solution, for specified range of the variables. Results complement recent approximate solutions which are valid only for the limited condition of the dimensionless angular frequency being less than or equal to unity, whereby suggesting a new Stokes number.

Hydrodynamics and effect of velocity on particle filtration due to bridging in water-saturated porous media using CFD-DEM simulation.

Particle bridging owing to the confinement of the pore structure affects the transport and retention of particles in porous media. Particle motion driven by gravities were well investigated, whose filtration is mainly affected by the ratio of the particle diameter to the pore throat size of the medium. However, particles whose motions are driven by the fluid is essential to be investigated for particle separation from the carrying fluid. In this study, the motion of particles was driven by the liquid when passing through a water-saturated porous medium. The fluid-particle flow in a porous medium was modeled using computational fluid dynamics-discrete element method. The motion of particles in the slurry was traced in the porous medium, which enabled particle clogging to be directly precited by the interaction between the particles and pore surfaces by assessing the exact location of each particle. The pressure and flow field of the liquid were investigated, and the variation in flow path owing to particle clogging was predicted. The hydrodynamic study also showed that the Stokes number and particle concentration determined the particle clogging at the pore throats of the porous medium. Increasing the fluid velocity of particles such that the Stokes number was almost equal to 1 increased the separation efficiency of particles. Further increasing the fluid velocity reduced the residence time, which reduced the separation efficiency of the particles.

Particle deposition and fluid flow characteristics in turbulent corrugated pipe flow using Eulerian-Lagrangian approach.

A numerical simulation of aerosol particle deposition in a horizontal circular pipe with a corrugated wall under turbulent flow has been carried out in this research. This paper uses the RNG k-ε turbulence model with Enhanced Wall Treatment to simulate fluid flow. Furthermore, the Lagrangian particle tracking model simulates particle deposition in the corrugated pipe. Air-particle interaction is influenced by Stokes number, surface roughness, flow velocity, particle diameter, and pipe diameter. For the parametric simulation, particle diameter varies from 1 to 30 µm, whereas the Reynolds number ranges from 5000 to 10,000. The effect of corrugation height and pipe diameter on deposition efficiency is also investigated. This study shows that corrugation height significantly increases particle deposition compared to the smooth wall pipe. As the pipe diameter decreases, keeping the corrugation ratio constant, deposition efficiency also increases. Moreover, high flow velocity enhances deposition efficiency for particle diameters lower than 5 µm.

Drift prediction of pyroclasts released through the volcanic activity of Fukutoku-Okanoba into the marine environment.

On August 13, 2021, a submarine volcano Fukutoku-Okanoba erupted, and there was massive release of pyroclasts into the Pacific Ocean. Pyroclasts are chemically stable and continue to float near the surface of the sea, which can affect vessel navigation. Here, a simulation model that predicts the behavior of pyroclasts in the marine environment with practical accuracy is proposed. This is a simple model based solely on the terminal velocity of pyroclasts without being weathered by external forces. On the whole, the model simulation reproduces the drifting positions obtained by actual observations. By using the results, the behavior of pyroclasts around the hull is organized based on the Stokes number. The results indicate that the maximal diameter of the pyroclasts moving along the streamline increases with the overall length of the ship but decreases with its speed.

Empirical Deposition Correlations.

Traditionally, empirical correlations for predicting respiratory tract deposition of inhaled aerosols have been developed using limited available in vivo data. More recently, advances in medical image segmentation and additive manufacturing processes have allowed researchers to conduct extensive in vitro deposition experiments in realistic replicas of the upper and central branching airways. This work has led to a collection of empirical equations for predicting regional aerosol deposition, especially in the upper, nasal and oral airways. The present section reviews empirical correlations based on both in vivo and in vitro data, which may be used to predict total and regional deposition. Equations are presented for predicting total respiratory deposition fraction, mouth-throat fraction, nasal, and nose-throat fractions for a large variety of aerosol sizes, subject age groups, and breathing maneuvers. Use of these correlations to estimate total lung deposition is also described.

Breath Hold Facilitates Targeted Deposition of Aerosolized Droplets in a 3D Printed Bifurcating Airway Tree.

The lungs have long been considered a desired route for drug delivery but, there is still a lack of strategies to rationally target delivery sites especially in the presence of heterogeneous airway disease. Furthermore, no standardized system has been proposed to rapidly test different ventilation strategies and how they alter the overall and regional deposition pattern in the airways. In this study, a 3D printed symmetric bifurcating tree model mimicking part of the human airway tree was developed that can be used to quantify the regional deposition patterns of different delivery methodologies. The model is constructed in a novel way that allows for repeated measurements of regional deposition using reusable parts. During ventilation, nebulized ~3-micron-sized fluid droplets were delivered into the model. Regional delivery, quantified by precision weighing individual airways, was highly reproducible. A successful strategy to control regional deposition was achieved by combining an inspiratory wave form with a "breath hold" pause after each inspiration. Specifically, the second generation of the tree was successfully targeted, and deposition was increased by up to four times in generation 2 when compared to a ventilation without the breath hold (p < 0.0001). Breath hold was also demonstrated to facilitate deposition into blocked regions of the model, which mimic airway closure during an asthma that receive no flow during inhalation. Additionally, visualization experiments demonstrated that in the absence of fluid flow, the deposition of 3-micron water droplets is dominated by gravity, which, to our knowledge, has not been confirmed under standard laboratory conditions.

Numerical investigation on the solid particle erosion in elbow with water-hydrate-solid flow.

Erosion in pipeline caused by solid particles, which may lead to premature failure of the pipe system, is regarded as one of the most important concerns in the field of oil and gas. Therefore, the Euler-Lagrange, erosion model, and discrete phase model are applied for the purpose of simulating the erosion of water-hydrate-solid flow in submarine hydrate transportation pipeline. In this article, the flow and erosion characteristics are well verified on the basis of experiments. Moreover, analysis is conducted to have a good understanding of the effects of hydrate volume, mean curvature radius/pipe diameter (R/D) rate, flow velocity, and particle diameter on elbow erosion. It is finally obtained that the hydrate volume directly affects the Reynolds number through viscosity and the trend of the Reynolds number is consistent with the trend of erosion rate. Taking into account different R/D rates, the same Stokes number reflects different dynamic transforms of the maximum erosion zone. However, the outmost wall (zone D) will be the final erosion zone when the value of the Stokes number increases to a certain degree. In addition, the erosion rate increases sharply along with the increase of flow velocity and particle diameter. The effect of flow velocity on the erosion zone can be ignored in comparison with the particle diameter. Moreover, it is observed that flow velocity is deemed as the most sensitive factor on erosion rate among these factors employed in the orthogonal experiment.

Penetration of inhaled aerosols in the bronchial tree.

It has long been recognized that the pattern of particle deposition in the respiratory tree affects how far aerosols penetrate into the deeper zones of the arterial tree, and hence contribute to either their pathogenic potential or therapeutic benefit. In this paper, we introduce an anatomically-inspired model of the human respiratory tree featuring the generations 0-7 in the Weibel model of respiratory tree (i.e., the conducting zone). This model is used to study experimentally the dynamics of inhaled aerosol particles (0.5-20µm aerodynamic diameter), in terms of the penetration fraction of particles (i.e., the fraction of inflowing particles that leave the flow system) during typical breathing patterns. Our study underline important modifications in the penetration patterns for coarse particles compared to fine particles. Our experiments suggest a significant decrease of particle penetration for large-sized particles and higher respiratory frequencies. Dimensionless numbers are also introduced to further understand the particle penetration into the respiratory tree. A decline is seen in the penetration fraction with decreasing Reynolds number and increasing Stokes number. A simple conceptual framework is presented to provide additional insights into the findings obtained.

[Impact of Collision Removal of Rainfall on Aerosol Particles of Different Sizes].

The impact of collision removal of rainfall on aerosol particles of different sizes was analyzed through the calculation of Stokes number, combining with the hourly PM2.5 concentrations and meteorological data in Haidian from October 2012 to October 2014, and also the size distribution data in a selected rainfall process. The calculation results of Stokes number showed that the raindrops had little effect on direct collision removal of aerosol particles of smaller than 2 µm, and had more effect on aerosol particles of larger than 2 µm. Based on the statistical analysis of the observation data, the precipitation processes or the precipitation hours with significantly decreased PM2.5 were quite limited. However, PM2.5 concentrations were increased in 43.2% of the precipitation hours. By analyzing the size distribution data of aerosol particles during a typical precipitation process, we found that the precipitation had significant scavenging effect on Aitken mode particles (<0.1 µm) and coarse mode particles (>1.0 µm), except for the accumulation mode particles. Since the accumulation mode aerosols contributed most of the mass of PM2.5, the rainfall processes only had minor influence on the collision scavenging of PM2.5.

A computational prediction for the effective drug and stem cell treatment of human airway burns.

Burns in the airway from inhaling hot gases lead to one of the most common causes of death in the United States. In order to navigate tissues with large burn areas, the velocity, temperature, and heat flux distributions throughout the human airway system are computed for the inhalation of hot air using the finite-element method. From there, the depth of burned tissue is estimated for a range of exposure times. Additionally, the effectiveness of drug or stem cell delivery to the burned airway tissue is considered for a range of drug or cell sizes. Results showed that the highest temperature and lowest heat flux regions are observed near the pharynx and just upstream of the glottis. It was found that large particles such as stem cells (>20 µm) are effective for treatment of the upper airways, whereas small particles (<10 µm) such as drug nanoparticles are effective in the lower airways.