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Abstract This paper presents a numerical evaluation of the eddy viscosity turbulence models (the zero-equation, one-equation, k - ε group and k - ω group models) in terms of CFD modelling of convection-radiation coupled heat transfer in indoor environment. The results show that all the models except the zero-equation model have acceptable accuracies to predict the bulk air temperature. However, the zero-equation and one-equation models seriously overpredict the convective heat transfer coefficient at the heater surfaces while the k - ε group models severely underpredict it, ultimately resulting in the incorrect predictions of the thermal buoyancy flows and contaminant dispersion. On the contrary, the k - ω group models perform best to calculate the convection-radiation heat split, which is critical to the successful predictions of the near-wall flow field and distribution patterns of the contaminants. This study also demonstrates the importance of simultaneously considering the convective and radiative heat transfer mechanisms when evaluating the turbulence models for indoor environment simulations. [ABSTRACT FROM AUTHOR]

Liver fibrosis is one of the leading causes of hepatic sclerosis and hepatocellular carcinoma worldwide. However, the complex pathophysiological mechanisms of liver fibrosis are unknown, and no specific drugs are available to treat liver fibrosis. Atractylenolide III (ATL III) is a natural compound isolated from the plant Atractylodes lancea (Thunb.) DC. that possesses antioxidant properties and the ability to inhibit inflammatory responses. In this study, cholestatic hepatic fibrosis was induced in mice using a bile duct ligation (BDL) model and treated with 10 mg/kg and 50 mg/kg of ATL III via gavage for 14 days. ATL III significantly reduced the liver index, lowered serum ALT and AST levels, and reduced liver injury in bile-duct-ligated mice. In addition, ATL III significantly attenuated histopathological changes and reduced collagen deposition. ATL III reduced the expression of fibrosis-related genes α-smooth muscle actin (α-SMA), Collagen I (col1a1), Collagen IV (col4a2), and fibrosis-related proteins α-SMA and col1a1 in liver tissue. Using RNA sequencing (RNA-seq) to screen molecular targets and pathways, ATL III was found to affect the PI3K/AKT singling pathway by inhibiting the phosphorylation of PI3K and AKT, thereby ameliorating BDL-induced liver fibrosis. Gas chromatography–mass spectrometry (GC-MS) was used to evaluate the effect of ATL III on liver metabolites in BDL mice. ATL III further affected glutamine metabolism by down-regulating the activity of glutamine (GLS1) and glutamine metabolism. ATL III further affected glutamine metabolism by down-regulating the activity of glutaminase (GLS1), as well as glutamine metabolism. Therefore, we conclude that ATL III attenuates liver fibrosis by inhibiting the PI3K/AKT pathway and glutamine metabolism, suggesting that ATL III is a potential drug candidate for treating liver fibrosis. [ABSTRACT FROM AUTHOR]

Abstract: Two computational models of the airway tree up to six generations deep were reconstructed from computed tomography scans from a single patient. The first scan was taken a day after an acute asthma episode while the second scan was taken 30 days later when the patient had recovered. The reconstructed models were used to investigate the effects of acute asthma on realistic airway geometry, the airflow patterns, the pressure drop, and the implications it has on targeted drug delivery. Comparisons in the geometry found that in general the average increase in diameter was larger in the right airway the airway is larger in diameter than the left side. The average airway branch difference from the Asthma Model to the Recovered Model was found to be 10.4% in the right airway and 4.8% in the left airway; however the airway dilation during the recovery stage was not consistent through the entire branch airway. Instead there were local branches that exhibited a very high local dilation recovery (≈30% recovery). This inconsistent dilation recovery makes it difficult to predict where and how much each branch will recover from an asthma episode. In terms of targeted drug delivery studies in the lung airways, the deposition patterns will be under-predicted for airway models that are reconstructed from a healthy or non-asthma affected lung airway. The discrepancy may reach as high as 13% between the two models for particles ≥10μm under a turbulent flow. For particles <10μm, the discrepancy reduces to 1% as the particle size reduces to 1μm under a turbulent flow. This means that drug delivery studies in the lung airway should consider the effects of airway narrowing and that if a recovered or a healthy airway is used, then the deposition fraction and efficiencies are expected to be under-predicted. [Copyright &y& Elsevier]

Abstract: In a chamber of the heart, large-scale vortices are shown to exist as the result of the dynamic blood flow and unique morphological changes of the chamber wall. As the cardiovascular flow varies over a cardiac cycle, there is a need for a robust quantification method to analyze its vorticity and circulation. We attempt to measure vortex characteristics by means of two-dimensional vorticity maps and vortex circulation. First, we develop vortex component analysis by segmenting the vortices using an data clustering algorithm before histograms of their vorticity distribution are generated. The next stage is to generate the statistics of the vorticity maps for each phase of the cardiac cycle to allow analysis of the flow. This is followed by evaluating the circulation of each segmented vortex. The proposed approach is dedicated to examining vortices within the human heart chamber. The vorticity field can indicate the strength and number of large-scale vortices in the chamber. We provide the results of the flow analysis after vorticity map segmentation and the statistical properties that characterize the vorticity components. The success of the cardiac measurement and analysis is illustrated by a case study of the right atrium. Our investigation shows that it is possible to utilize a data clustering algorithm to segment vortices after vorticity mapping, and that the vorticity and circulation analysis of a chamber vorticity can provide new insights into the blood flow within the cardiovascular structure. [Copyright &y& Elsevier]

Recurrent epidemics of respiratory infections have drawn attention from the academic community and the general public in recent years. Aircraft plays a pivotal role in facilitating the cross-regional transmission of pathogens. In this study, we initially utilized an Airbus A320 model for computational fluid dynamics (CFD) simulations, subsequently validating the model's efficacy in characterizing cabin airflow patterns through comparison with empirical data. Building upon this validated framework, we investigate the transport dynamics of droplets of varying sizes under three air supply velocities. The Euler-Lagrangian method is employed to meticulously track key parameters associated with droplet transport, enabling a comprehensive analysis of particle behavior within the cabin environment. This study integrates acquired data into a novel PCR (Personal Contamination Rate) equation to assess individual contamination rates. Numerical simulations demonstrate that increasing air supply velocity leads to enhanced stability in the movement of larger particles compared to smaller ones. Results show that the number of potential infections in the cabin decreases by 51.8% at the highest air supply velocity compared to the base air supply velocity, and the total exposure risk rate reduced by 26.4%. Thus, optimizing air supply velocity within a specific range effectively reduces the potential infection area. In contrast to previous research, this study provides a more comprehensive analysis of droplet movement dynamics across various particle sizes. We introduce an improved method for calculating the breathing zone, thereby enhancing droplet counting accuracy. These findings have significant implications for improving non-pharmacological public health interventions and optimizing cabin ventilation system design. [ABSTRACT FROM AUTHOR]

The natural circulation loop is crucial for the safe and stable operation of nuclear reactors and other applications. Traditional numerical algorithms, based on the Boussinesq approximation, have limitations when dealing with large temperature differences and density disparity, and they do not fully address fluid compressibility. This paper adopts the decoupled and stabilized lattice Boltzmann method (DSLBM) with a non-Boussinesq algorithm to study the natural circulation loop. The DSLBM provides a detailed flow description under large temperature and density differences, incorporating the pseudopotential multiphase model, temperature equation, and state equation, without relying on assumptions. The study examines the loop's performance under various temperature differences, central height differences, and heating source lengths, focusing on mass flow rate, driving head, and heating power. It reveals the energy performance, flow characteristics, and heat transfer properties of the loop, highlighting the physical mechanisms involved. Comparison with the empirical formulation of the incompressible equation from the theoretical aspect shows that when the temperature difference coefficient is lower than 0.15, the two methods are not much different from each other. When the temperature difference coefficient reaches 0.2, 0.3, and 0.4, the difference between the two methods is 9.47%, 19.11%, and 42.64%, respectively. Consequently, the Boussinesq approximation can be compensated by DSLBM, which proves the value of the application of the algorithm in exploiting the compressibility of fluids. The dimensionless fitting correlation with greater universality is obtained, which helps to predict the properties of the natural circulation loop with varying temperature differences, friction coefficients, and geometric structures. The research in this paper will lay the foundation for optimizing the system design of the natural circulation loop and improving energy utilization efficiency. [ABSTRACT FROM AUTHOR]

Although wind-buoyancy interactions have been widely explored, their mixing associated with semi-transparent facades are not yet clearly understood. This gap greatly restraints the implementation of naturally ventilated double-skin facades (NVDSFs). In this study, the impact of wind on the buoyancy flow in an NVDSF was investigated on a range of wind speeds, wind angles, and solar radiation intensities. The wind's realistic impinging associated with solar radiation's transportation between facades are revealed. Results present three aspects: the impact of wind on façade temperatures; the counteraction of wind on buoyant outflow; and defining and correlating the 'critical wind velocity' according to targeted natural ventilation rates. Results correlated the additional temperature drops on the outer glazing for wind speed 0.125–1.0 m/s, attack angles 5° ∼ 85° and solar radiation between 200–1000 W / m 2. The wind at 1 m/s and 5° can cause 10.5% reduction in façade temperature. By proposing a 'wind inflow coefficient', we established an empirical model to calculate the total ventilation rate under the mixed wind-buoyancy effect. Furthermore, an important concept – 'critical wind velocity', was introduced accordingly. It indicates the wind velocity under which the targeted natural ventilation can be met for an NVDSF for different solar conditions, e.g. the velocity at which the wind cancels out the buoyant outflow or below which the indoor ventilation can be satisfied. The novel correlations for the combination of mixed wind-buoyancy field with solar radiation and glazing materials can contribute significantly to NVDSFs under realistic environmental conditions. • Impacts of wind speeds and directions on buoyancy-driven flow identified. • Empirical correlations between wind factors and NVDSFs performance obtained. • Critical velocities at which buoyancy flow is cancelled by wind addressed. • Model to predict total natural ventilation rates under wind conditions proposed. [ABSTRACT FROM AUTHOR]

Choledochal cysts (CCs) are an important risk factor for cholangiocarcinoma, though their etiology remains debated. Given the vital role of bile fluid in digestive processes within the biliary system, examining such mechanisms from the perspective of bile fluid dynamics may offer additional insights for clinical use. This study utilized magnetic resonance imaging (MRI)-based patient-specific scans for detailed reconstruction and further employed the computational fluid dynamic method to assess the physiological functions of each system, including refilling and emptying processes. The impact of bile rheological property was also examined. Key biomechanical parameters—pressure and wall shear stress (WSS)—were displayed on a two-dimensional plane via surface mapping for enhanced visualization and comparative analysis. Outcomes demonstrated a significant reduction in bile flow velocity in CCs patients due to common bile duct's anatomical features and bile's shear-thinning, non-Newtonian nature, with a notable increase in pressure drop observed. In healthy biliary systems, WSS variations were minimal; however, in CCs patients, extreme WSS differences were found, with the highest WSS in the segmental bile duct and the lowest in the dilatation area, presenting a magnitude difference of approximately 1000. CCs one showed WSS levels 100–250 times higher than healthy ones in the common bile duct. Bile rheological properties substantially affect pressure and WSS patterns, particularly WSS, where pathological bile caused a tenfold increase in WSS compared to healthy bile. The findings aimed to enhance the understanding of biliary fluid mechanics in CCs and offer insights into selected fluidic variables for future microfluidic chip experiments. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editors discuss articles in the issue on topics including heat exchangers, evaporative cooling effect and stratified thermal energy storage systems.

This study utilizes the finite volume method with a two-fluid model to analyze water characteristics in a boiling channel when density wave oscillation occurs. A 2-D numerical model is utilized to characterize both axial and radial mass and energy exchange, as well as the mechanisms involving flow and heat transfer during density wave oscillation under uniform and non-uniform heating conditions. The numerical model was used to predict the heating power threshold values of two-phase water flowing upward in a vertical pipe under type II density wave oscillation at the working pressure and an inlet–outlet pressure difference of 125 kPa, when the average heating power increased from 44.06 kW/m2 at a speed of 0.5 kW/(m2·s). The flow and heat transfer characteristics before and after the type II density wave oscillation were determined and compared to the flow and temperature fields at various moments. Along the pipe axis, the wall heat flux was loaded under uniform, standard-sine, and inverted-sine types, which represent three typical types of wall heat flux arrangements. Flow oscillation appeared the earliest under the inverted-sine-type heat flux with low vapor quality (approximately 0.13) with a void fraction of 0.6 at the outlet. [ABSTRACT FROM AUTHOR]

Natural convection is widely observed in various scales of natural phenomena and industrial applications. The low Mach number (i.e., low-velocity) natural convection, especially under large temperature differences and significant density and pressure fluctuations, is of great research significance in industrial fields such as nuclear engineering. The Boussinesq approximation based on the incompressible Navier–Stokes (NS) equation is not fully descriptive due to the neglect of coupling effects among temperature, density, and pressure. As for numerical algorithms based on the compressible Navier–Stokes equation, they often suffer from high computational costs and convergence difficulties. In this paper, a novel numerical algorithm based on the decoupled and stabilized Lattice Boltzmann multiphase model with a complete physical description and clear conceptual framework is proposed. It couples the equation of state and the temperature equation, considering the full effects of gravity, pressure, and temperature-dependent density on flow disturbances, and it recovers the complete compressible NS equation. Taking the natural convection in an enclosed cavity as an example, the non-dimensional numbers governing the fluid system are identified by Buckingham π theorem; thus, a new thermal expansion number is proposed to connect the pressure effect. The accuracy and reliability of the numerical algorithm are validated by comparing it with standard benchmarks. On this basis, the proposed algorithm enables a unified physical description from low to high Rayleigh numbers and from small to large temperature differences. By analyzing the flow and heat transfer characteristics of natural convection under different Rayleigh numbers, temperature differences, and thermal expansion numbers, this study reveals the coupled physical mechanisms of low Mach number flow from small to large temperature differences, from low to high Rayleigh numbers and under different thermal expansion numbers. [ABSTRACT FROM AUTHOR]

• HTC dominated by microscopic geometrical features. • Classic theory not applicable to nanoengineered surfaces. • Evaporation-induce negative pressure is critical. • Separate liquid and vapor paths are also important. Nanostructured surfaces present great potentials to enhance nucleate boiling heat transfer. However, due to the diverse materials and approaches of fabrication, nanostructured surfaces have a wide range of micro/nano-morphologies and different or even conflicting effects on the critical heat flux (CHF) and heat transfer coefficient (HTC), causing serious uncertainties to the design of optimal nanostructures for thermal management. The mechanisms behind the uncertainties are yet to be fully understood. This paper presents a comprehensive review of the nanostructures, bubble dynamics phenomena and boiling heat transfer performance of various nanoengineered surfaces. It is proposed that the evaporation of liquid menisci in nanoscale pores triggers a significant negative pressure in the porous structures, which causes an additional heat and mass transfer mechanism and significantly changes the features of bubble nucleation, growth and departure, as well as the CHF and HTC. However, the effectiveness of the negative pressure is highly sensitive to the geometrical features of the porous nanostructures. Therefore, the key job when designing optimised nanostructures for enhancing nucleate boiling is to create optimal hybrid micro/nanostructures that can boost the generation of negative pressure, liquid supply towards and removal of vapor away from the nucleation sites. [ABSTRACT FROM AUTHOR]

Highlights: • The SST k-ω model performs best for convection-radiation hybrid thermal airflows. • Surface radiation affects airflow pattern via heating up surfaces. • Surface radiation affects VOC emission and dispersion. Abstract This study presents a computational fluid dynamics (CFD) study on the effects of surface radiation on the emission and dispersion of gaseous contaminants in indoor spaces. Mathematical models are firstly validated against experimental data reported in the literature. It demonstrates that the Shear Stress Transport (SST) k-ω model performs best among other turbulence models when modelling convection-radiation hybrid heat transfer. The study also reveals that surface radiation accounts for 37%–71% of the heat dissipation from the heat sources in a typical office room, which remarkably alters the indoor airflow pattern through cooling and heating the solid surfaces. Beyond that, the emission rate of volatile organic compounds (VOCs) from solid surfaces is also changed due to its dependence on the temperature. Consequently, the VOCs exhibit different dispersion characteristics and distribution patterns in the air, which ultimately results in different evaluations of the indoor air quality (IAQ). This study demonstrates that even in high-momentum indoor spaces such as those equipped with mixing ventilation systems, surface radiation still plays an important role in shaping the overall indoor environment quality (IEQ). [ABSTRACT FROM AUTHOR]

Abstract Intranasal drug delivery has attracted significant attention because of the opportunity to deliver systemic drugs directly to the blood stream. However, the mucociliary clearance poses a challenge in gaining high efficacy of intranasal drug delivery because cilia continuously carry the mucus blanket towards the laryngeal region. To better understand mucus flow behaviour on the human nasal cavity wall, we present computational model development, and evaluation of mucus motion on a realistic nasal cavity model reconstructed from CT-scans. The model development involved two approaches based on the actual nasal cavity geometry namely: (i) unwrapped-surface model in 2D domain and (ii) 3D-shell model. Conservation equations of fluid motion were applied to the domains, where a mucus production source term was used to initiate the mucus motion. The analysis included mucus flow patterns, virtual saccharin tests and quantitative velocity magnitude analysis, which demonstrated that the 3D-shell model results provided better agreement with experimental data. The unwrapped-surface model also suffered from mesh-deformations during the unwrapping stage and this led to higher mucus velocity compared to experimental data. Therefore, the 3D-shell model was recommended for future mucus flow simulations. As a first step towards mucus motion modelling this study provides important information that accurately simulates a mucus velocity field on a human nasal cavity wall, for assessment of toxicology and efficacy of intranasal drug delivery. [ABSTRACT FROM AUTHOR]

The mixing characteristics of cubic particles in a cylinder mixer are analyzed by the SIPHPM simulation in comparison with spherical particles. The assembly of cubic and spherical particles of uniform size is pre-divided into two parts in the axial, circumferential or radial directions respectively. Then they are mixed when the cylinder is rotated at different rotational speeds of Ω d  = 15–60 rpm. The mixing degree is evaluated by either the Lacey mixing index or the mixing information entropy. A normalized mixing entropy is proposed here to compare the absolute degree of mixing with non-equivalent particle numbers. It is found that, for cubes, the radial mixing efficiency is higher than the circumferential, and the radial and circumferential mixing degrees are both larger than the axial. Compared with spheres, cubic shape may enhance the circumferential mixing whereas reduce the axial mixing levels at high rotating speeds. However, at low rotating speed, cubic shape always reduces the degree of mixing of all the three patterns. Moreover, the axial dispersion characteristics are also explored by the probability density functions and the axial paths. The spatial and temporal diffusion coefficients of concentration and kinetic energies are illustrated and used to explain the axial dispersion mechanism in analogy with diffusion equation. The mean diffusion coefficient of rotational energy is independent of rotating speed, which means the axial diffusion of rotational energy depends on the eccentric feature of cubic particle, i.e. rotational ability. In contrast, it is preferred to regard the axial dispersion mechanism of spheres as convection rather than diffusion. [ABSTRACT FROM AUTHOR]

In conventional CFD-DEM based on the cell-averaged-volume-fraction (CAVF), mesh size for gas phase is required to be larger than particle size. It is good for fine particles, whereas too coarse for large particles. A conservative virtual volume fraction method is proposed here for sub-particle LES-DEM coupled simulation of large particles. Although still based on CAVF, mesh size is smaller than particle size, and the LES-DEM coupled solution on finer grids incorporating the Smagorinsky sub-grid-scale stress tensor is proposed. The feedback force is redistributed onto the finer grids to perform the four-way coupling on fine scales. It is conservative for the inter-phase interactions between the super-particle (for drag force) and sub-particle (for feedback force) scales through the same distribution function. The 2D case and the 3D cases with or without LES are performed to demonstrate the capability of this model, and validated by an experiment of spouted bed. The important features on gas-phase are illustrated to demonstrate the application for capturing the gas-phase behavior on sub-particle scales. [ABSTRACT FROM AUTHOR]

Robust predictive models of dynamic bubbly systems of nanoparticle-liquid mixtures are vital to the design and assessment of relevant industrial systems. Previous attempts to model bubbly flows of dilute nanofluids using the classic two-phase flow models were unsuccessful although the apparent hydrodynamic properties of the dilute nanoparticle-liquid mixtures were only negligibly different to those of their pure base liquids. Emerging studies demonstrated that when bubbles exist in the mixture, nanoparticles tend to spontaneously aggregate at the bubble interface, forming a layer of “colloidal armour” and making the bubble interface partially rigid and less mobile. The colloidal armour also significantly modifies the characteristics of the bubble-liquid and bubble-bubble interactions. Therefore, it was proposed that the key job when developing a predictive model based on classic two-phase flow models is to re-formulate the bubble-liquid and bubble-bubble interactions. However, the adsorption of nanoparticles in dynamic bubbly systems has rarely been studied. The lack of mechanistic understanding has severely hindered the model development. Therefore, this study reviews the common findings yielded from experimental and numerical investigations reported in literature, with the aim to clarify the critical points to address when modelling bubbly flows containing nanoparticles using the classic two-fluid and MUSIG models. [ABSTRACT FROM AUTHOR]

The motion of three-dimensional cubic particles in a thin rotating drum is simulated by the SIPHPM method. The drums with frictional or smooth front and rear walls, and the particles of cubic and spherical shapes, and different particle numbers are considered to study the effect of cubic particle shape, end-wall frictions and filling levels. Different flow patterns of cubic particles are observed, which are significantly dominated by the friction from the end-walls. The probability density function of velocity components, the flatness factors are used to analyze the motion behaviour of cubic particle. The Froude number, ensemble mean and time averaged particle velocities are also analyzed. A primary and secondary mode of driving from the end-wall frictions are indicated and the mechanisms on the influences of wall friction, particle shape and filling levels are fully explained. [ABSTRACT FROM AUTHOR]

Human-induced wake flow characteristics and its interaction with thermal conditions was investigated by performing CFD simulations with dynamic-meshing of a moving manikin model. The manikin motion with and without swinging limbs was achieved by the re-meshing method to update the grid with each time step. The results focused on determining what discrepancies are produced in the flow field by a simplified geometry in the form of a cylinder, swinging limbs and thermal conditions; and whether such assumptions can be made for larger multi-body analysis. Using a cylinder showed differences in the velocity field behind the head and leg gap. The flow field between the rigid motion and swinging limb motion, showed significant discrepancies which corresponded to the gait phase. There were increased airflow disturbances at the hands and ankles (furthest body parts from the pivot point). The influence of thermal plume on the wake flow was minor during walking motion because of the walking speed of 1.2 m/s which dominated the buoyant thermal plume velocity. However, after the manikin stopped moving the thermal plume velocity became comparable to the residual wake. [ABSTRACT FROM AUTHOR]

Bubbly flows of air-water and air-nanofluid were investigated numerically using the two-fluid model. Through comparing the predicted bubble velocity and void fraction profiles against the experimental data, the classic two-fluid model, which has been widely validated for two-phase flows of pure liquids, was found to be inapplicable to those of nanofluids because of the empirical nature of the interfacial force formulation. The roles of interfacial forces were believed to be significantly altered in nanofluids rather than in pure liquids due to the spontaneous phenomenon of nanoparticle adsorption at bubble interfaces. Because of the nanoparticle layer, bubbles submerged in nanofluids would partially behave like a rigid sphere and develop a rotation movement. A slanted wake could be induced behind the bubble, generating a lateral Magnus force pointing towards the pipe centre and consequently making the positive-to-negative reversion of lift force occur at a smaller bubble diameter. Meanwhile, the slanted wake would also make bubbles in the viscous regime experience a drag force similar to that in the distorted regime, which makes the viscous-to-distorted transition point occur at a smaller bubble Reynolds number. It was recommended that the most important task when modelling bubbly flows of nanofluids using the two-fluid model is to reformulate the interfacial forces accounting for the effects of nanoparticle adsorption. [ABSTRACT FROM AUTHOR]

The discharge of regular noncircular particles through a hopper orifice is simulated by discrete element method. A novel approach of incorporating distributed sub-spheres around the non-spherical particle borders is developed. The aim of this work is to explore the effect of roundness on the discharge behavior as well as relevant mechanisms of hopper discharge. Seven types of non-spherical particles, i.e. triangular, quadrilateral, pentagonal, hexagonal, heptagonal, octagonal and decagonal shaped particles, are chosen for comparative study. They are respectively discharged freely from the hopper beds of three different base angles, i.e. α = 65, 70 and 75 ° . The discharge process, fraction, flow rate, and voidages are analyzed to show the effect of particle roundness on discharge characteristics. [ABSTRACT FROM AUTHOR]

With the fast development of nanotechnology, accurate measurement and classification of nanoparticles are in great need. Nanoparticles frequently appear in non-spherical forms such as long aspect ratio nanofibers, nanotubes, and irregular nano-agglomerates. While the well-developed classical studies were mainly in continuum regime with spherical particles, dynamics of the non-spherical nanoparticles is not fully understood. In this study, orientation-averaged mobility of nanofiber and nanorod (with no preferred alignment) is examined by the methods of Brownian diffusion theory, a combination of collision limited reaction rate theory and the bipolar diffusion charging analysis. Comparisons to empirical predictions from the experimental measurements are also made. The study leads to the discovery of a surface-dominated mobility for high aspect ratio nanoparticles with characteristic Knudsen number greater than 5. In view of the extreme relative length scales between particle size and the gas mean free path, particles of all morphologies can be viewed as point collisions; therefore, the equivalent surface mobility diameter is reasonably justified. This finding has been verified in the current study with high aspect ratio particles. For non-spherical particles of more general forms, further investigation is needed. As expected, accuracy of this approximation reduces as the characteristic Knudsen number decreases. WhenKn(dL) < 0.1, the study shows that particle morphology starts to play an important role. A review of particle mobility for all Knudsen number flows is also provided. © 2017 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

• An experimental platform of the HSGHE was introduced. • The energy efficiency of the HSGHE at different nanofluid concentrations were compared. • Compared to the base liquid, the nanofluid increased the heat exchange rate of the HSGHE. • Low-concentration nanofluids increased the performance of the HSGHE. The thermal performance of a ground heat exchanger (GHE) largely depends on the heat transfer fluid circulating in the system. In this study, a laboratory test apparatus for a horizontal spiral-coil ground heat exchanger (HSGHE) was designed and constructed to investigate the effects of different volume fractions of CuO/water nanofluid on the energy efficiency of the HSGHE. The results showed that, at a volumetric fraction of 1%, the CuO/water nanofluid led to a 9.4% increase in the heat exchange rate of the HSGHE, compared to water. In addition, the heat transfer enhancement effect at a lower volume fraction of the CuO/water nanofluid was greater than the effect of its viscosity on the performance of the HSGHE. The CuO/water nanofluid with a volumetric fraction of 1% was not recommended for use in the HSGHE owing to its performance efficiency coefficient (PEC) of less than 1. The optimal volume fraction was 0.5%, at which the PEC was the highest (1.025). Therefore, it was determined that the utilization of a low volume fraction of CuO/water nanofluid in HSGHE provides energy efficiency enhancements independent of the GHE design. [ABSTRACT FROM AUTHOR]

Laboratory animals have historically performed a vital function in evaluating health effects of human exposure to ambient particulate matter (PM). Due to the complexity of particle-laden flows and airway interactions that involve multiple species, in-depth knowledge of airflow and particle transport in both the non-human primate surrogates and human airways is still lacking. To advance the understanding in this field, this paper presents a numerical study that investigated the airflow and particle deposition characteristics of inhaled PMs in monkey and human nasal airways. Anatomically accurate macaca fuscata monkey and human nasal cavity models were reconstructed from CT images, micron particles with diameters less than 10 μm were included to conduct in silico exposure studies. Resultant particle deposition patterns were quantified by deposition enhancement factor (DEF) and deposition intensity (DI) along the airways to provide profound understanding of the similarities and differences in particle inhalation exposure characteristics across species. Anatomy comparison showed that the convoluted nasal passage of the monkey airway possessed higher level of complexity in terms of the surface-area-to-volume ratio compared to the two human nasal models, which could lead to higher evaluated nasal exposure to airborne particulate matter. Similar airflow patterns were observed from streamlines and wall shear stress distributions in all three nasal cavities of two species, with bulk air concentrated mainly in the middle and inferior meatuses in the nasal chambers. Despite the evidenced inter-subject deposition variations presented in all considered nasal cavity models, strong and similar micron particle deposition preferences with comparable DEF and DI levels were observed along the floor region of middle and inferior meatuses for both species. The methods and research findings presented in this work represent critical, initial steps towards establishing high-fidelity qualitative and quantitative linkages between the two species that enable more effective laboratory data extrapolations, improve study design, and facilitate validations of in vitro techniques currently being developed as part of international efforts to reduce or replace the use of animals in toxicity assessments for aerosol exposures. • Higher level of surface-area-to-volume ratio was found in the monkey nasal airway compared to the two human models. • Similar airflow patterns were observed in all three nasal cavities of two species. • Similar micron particle deposition preferences were found along the floor of middle and inferior meatuses for both species. • This work shows critical, initial steps towards establishing high-fidelity extropolation approach between the two species. [ABSTRACT FROM AUTHOR]

Acute lung injury (ALI) is a syndrome caused by an excessive inflammatory response characterized by intractable hypoxemia both inside and outside the lung, for which effective therapeutic drugs are lacking. Atractylodis rhizoma, a traditional Chinese medicine, has excellent anti-inflammatory and antiviral properties in addition to protecting the integrity of the cellular barrier. However, few studies of Atractylodis rhizoma for the treatment of ALI have been published, and its mechanism of action remains unclear. In the present study, the chemical composition of the ethanolic extract of Atractylodis rhizoma (EEAR) was initially clarified by high performance liquid chromatography (HPLC), after which it was studied in vivo using a lipopolysaccharide (LPS)-induced ALI rat model. Treatment with EEAR significantly reduced the lung wet/dry (W/D) ratio, neutrophil infiltration, and malondialdehyde (MDA) and myeloperoxidase (MPO) formation, and enhanced superoxide dismutase (SOD) and glutathione (GSH) depletion in rats with ALI, thereby improving lung barrier function and effectively reducing lung injury. In addition, EEAR significantly reduced histopathological changes, decreased the expression of inflammatory factors (such as tumor necrosis factor-α (TNF-α), interleukin-1 beta (IL-1β), inducible nitric oxide synthase (INOS), and cyclooxygenase-2 (COX-2)), and inhibited the activation of the NF-κB signaling pathway, thus reducing inflammation. In addition, EEAR was found to also reduce oxidative stress in ALI by upregulating the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream proteins heme oxygenase-1 (HO-1) and NADPH quinone acceptor oxidoreductase 1 (NQO-1). EEAR also reduced LPS-induced inflammatory factor expression in THP-1 cells in vitro by inhibition of the NF-κB signaling pathway, and reduced damage from lipopolysaccharide (LPS)-induced oxidative stress in THP-1 cells by promoting the expression of Nrf2 and its downstream targets HO-1 and NQO-1, the molecular mechanism of which was consistent with in vivo observations. Therefore, we conclude that EEAR attenuates oxidative stress and inflammatory responses via TLR4/NF-κB and Keap1/Nrf2 signaling pathways to alleviate LPS-induced ALI, suggesting that Atractylodis rhizoma is a potential drug candidate for the treatment of ALI. [ABSTRACT FROM AUTHOR]

In pursuit of stable operation in thermal hydraulic engineering, this paper researches two-phase flow through tube bundles by the lattice Boltzmann method. The single-relaxation-time lattice Boltzmann model and the multicomponent, multiphase pseudo-potential lattice Boltzmann model are adopted. Specifically, the two-phase flow past double-tandem circular cylinders, double-parallel circular cylinders, in-line tube bundles and staggered tube bundles with various spacing ratios is investigated. The vortex variable distribution and vortex shedding law under different working conditions are further compared to obtain the time-averaged drag, oscillating drag and Strouhal number. The variation law of lift coefficient and lift power spectrum with different spacing ratios is revealed. With increasing spacing ratio, the mutual interference between the double-tandem circular cylinders is weakened, the amplitude of the time-averaged drag on the double-parallel circular cylinders is reduced and the lift power spectrum changes from a double-peak distribution to a single-peak structure. The drag and lift of the center column of in-line tube bundles are lower than those on both sides, while the oscillating drag of the odd-row columns of staggered tube bundles is higher than that of even-row columns. These results contribute toward laying a solid foundation for future research on multiphase tube bundle flow issues in nuclear engineering. [ABSTRACT FROM AUTHOR]

The MUltiple-SIze-Group (MUSIG) model was used in this study to simulate bubbly flows of air–water and air–nanofluid in a vertical tube. Flow parameters including the void fraction, gas velocity, interfacial area concentration and Sauter mean bubble diameter were predicted and compared against the experimental data available in the literature. The model agreed well with the experimental data of air–water bubbly flow, but exhibited notable discrepancies from the data of air–nanofluid bubbly flow. With the aim to improve the MUSIG model for an effective modelling of air–nanofluid bubbly flows, some latest experimental and theoretical research outcomes were summarised and analysed. It was proposed that the key job when modelling bubbly flows of nanofluids using the MUSIG model is to address the spontaneous assembly of nanoparticles at bubble surfaces and its effects on the interfacial forces and bubble coalescence process. [ABSTRACT FROM AUTHOR]

The work deals with evaluation and simulation of the thermal discrete element method (TDEM) for particle-particle collision and thermal conduction in a packed bed. The effects of different granular properties, such as particle size, stiffness factor or compression degree, thermal diffusivity, void fraction or concentrations, and packing states, on the thermal conduction and insulation characteristics of granular assembly are discussed. The thermal conductivity and diffusion still play dominant roles in the overall thermal conduction and insulation of the granular bed. However, it is also indicated that increasing compression degree, reducing particle size and void concentration will increase the thermal conduction throughout the granular materials, and vice versa. [ABSTRACT FROM AUTHOR]

Particle diffusional losses in confined flows such as pipes are important for identification of erosion or accretion build-up. Its applications are varied and prominent in industrial and biomedical applications where essentially, tubular geometries transport fluid-particle flows. Computational modelling of dilute suspensions of ultrafine and nano-scale particles dispersing in a fluid often use the Lagrangian particle tracking approach. The Euler Implicit scheme in FLUENT v16 was evaluated for tracking such particles through a standard pipe geometry. It was found that the particles’ Brownian dispersion was dependent on the computational mesh, and the integration time step for a given particle size. For the pipe geometry well established analytical solutions for particle deposition efficiency are available to directly compare the simulated results. For irregular geometries (such as human respiratory anatomy) there are no analytical solutions and experimental deposition data is scarce and an alternative method is required to verify the simulation setup. In this case the computational models were set with zero velocity and the nanoparticles released from rest. The particle motion was then initiated purely by Brownian motion. The root mean square displacement was used to compare the time step size selector (either by the Length Scale Factor, L S , or the Step Length Factor SLF approach in FLUENT ; and a fixed time step using an in-house code ‘PARTICLE’ ). This provides a modelling verification framework to determine the most appropriate time step selection that reproduces the particle Brownian dispersion behaviour correctly. [ABSTRACT FROM AUTHOR]

A DEM study of a rocking particle bed is performed to show the effects of rocking frequency and amplitude on particle discharge. Six rocking frequencies of f r = 0, 0.1, 0.2, 0.3, 0.4, 0.5 Hz with seven rocking amplitudes of θ r = 5°, 15°, 30°, 45°, 60°, 75° are simulated respectively. The particle distributions, discharged fractions, flow rates, particle trajectories and kinetic energies are compared and analyzed in detail to show and explain the features of particle discharging process under different rocking conditions. The rocking frequency is found to be the primary factor to determine the direction of influence on particle discharge, i.e. either beneficial or detrimental, whereas the rocking amplitude is the secondary factor to magnify the primary influence on particle discharge. In addition, the flare angle of the bed can determine the mode of influence on particle discharge, i.e. either a linearly varied discharge or an oscillated variation of discharge. The results are helpful to improve the process control and optimal design of the particle discharge beds in many engineering applications. [ABSTRACT FROM AUTHOR]

Motion of nanoparticles suspended in fluids are dominated by Brownian diffusion—a physical property well understood following the work by Einstein in 1905. While theoretical derivation and experimental measurement of the diffusion coefficients for spherical particles are well developed, such information is lacking for non-spherical particles as the coupled rotational and translational motion hinders a clear description of the overall diffusive outcome. In this study, the Brownian diffusion of elongated nano-fibers is investigated numerically. Motion of the nano-fiber is resolved by solving the system of equations governing its coupled translational and rotational motion. To isolate the Brownian diffusion from other diffusive forces, test fibers are immersed in an unbounded quiescent fluid where only the hydrodynamic drag and Brownian forces are present. The study allows a close look at the Brownian diffusion of nano-fibers with respect to the translation, rotation, coupling, and how the rotation affects the particle's macroscopic diffusion properties. In this study, the Brownian diffusion of ellipsoidal particles are studied. The translational and the rotational Brownian motions and their coupling are included in the analysis. Particular attention was given to the rotational relaxation time in determining the non-spherical particle's isotropic and anisotropic diffusive properties. Theoretical and semi-empirical equations are developed to quantify the diffusion coefficients of nano-fibers. The predications are compared with available experimental data. The comparison to the analytic solution in the limiting case of a sphere is with excellent accuracy. The study opens up new approaches for studying fundamental diffusive processes of non-spherical elongated particles that are abundant in natural environment. Copyright © 2016 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

The bubbly flows of air–nanofluid and air–water in a vertical tube were numerically simulated using the two-fluid model. Comparison of the numerical results against the experimental data of Park and Chang (2011) demonstrated that the classic two-fluid model, although agreed well with the air–water data, was not applicable to the air–nanofluid bubbly flow. It was suggested that in a bubbly flow system, the existence of interfaces allows the spontaneous formation of a thin layer of nanoparticle assembly at the interfaces, which significantly changes the interfacial behaviours of the air bubbles and the roles of the interfacial forces. As the conservation equations of the classic two-fluid model are still applicable to nanofluids, the mechanisms underlying the modified interfacial behaviours need to be carefully taken into account when modelling air–nanofluid bubbly flows. Thus, one of the key tasks when modelling bubbly flows of air–nanofluid using the two-fluid model is to reformulate the interfacial transfer terms according to the interfacial behaviour modifications induced by nanoparticles. [ABSTRACT FROM AUTHOR]

Particle collision model plays an important role in Eulerian–Lagrangian simulation of particle-fluid flows. A new theoretical three-dimensional collision model for generalized non-spherical rigid particles is proposed by using an improved and generalized definition of the coefficient of restitution for general shape particles and following the fundamental laws of momentum, energy and friction. Moreover, the consistence between the present model and the existing hard sphere model under simplified conditions has been demonstrated by reducing the general solution to the special solution for spheres. This model is also validated by a numerical test of collision process between cubic particles using conservation laws and an experiment of collision between a brick particle and a flat surface. The validation work indicates the feasibility of this model to be used for general non-spherical particle-fluid flows. In addition, a particle discharging flow in a lifting hopper is simulated with satisfactory agreement with experimental results, which shows the successful demonstrative application of current model for complex particle flow simulation. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics simulations were conducted in this study to investigate the effects of the buoyancy-driven thermal plume on the airflow pattern and transport characteristics of airborne particles in airliner cabins. A cabin section containing three seats and three passengers was built and numerical simulations were conducted using thermal and isothermal conditions, respectively. Airborne particles were assumed to be released by the passengers through coughing. The predicted airflow field was validated using experimental data available in the literature. Comparison of the computational results revealed that the thermal plume significantly changed both the airflow filed and the trajectories of particle transport. In addition, the spatial distribution characteristics of the particles and their residence time in the passengers’ breathing zones were highly sensitive to the location of released particles. Comparatively, the particles released by the passenger seated close to the window may have the highest health risk to other two passengers. [ABSTRACT FROM PUBLISHER]

A thermal discrete element method (DEM) is used to simulate particle mixing and heat conduction inside wavy drums to explore the effects of wavy walls. Sinusoidal configurations with different waves on the walls are simulated. The Lacey mixing index is applied to analyze the mixing characteristics. The driven forces from the wavy wall, either positive/negative or effective driven forces, are analyzed to explain the mechanisms of mixing enhancement in the wavy drum. A new control parameter is proposed to explain the mechanism of mixing enhancement. It is found that a locally oscillating effect exists in wavy drums, which is imparted on the bulk rotating motions of particles and enhances the characteristics of particle mixing and heat conduction significantly. Except over large wave numbers and rotating speeds when the flow regime is deteriorated for mixing, the wavy drum is generally beneficial for mixing augmentation as well as conduction enhancement. [ABSTRACT FROM PUBLISHER]

An extended theoretical particle-to-wall collision model for the rigid particles of general shape is presented. It is based on an improved definition of the restitution coefficient, which is consistent with the previous definition of the restitution coefficient for spherical particles, but modified to meet the conditions of arbitrary non-spherical shapes. Moreover, it follows the fundamental conservation laws of momenta, as well as the Coulomb’s law of friction. In addition, this model is validated by comparing the simulation results to experimental measurements of the collision between rectangular particles and walls, which shows the correctness of the model. Finally, the applications of present model for multiple-impacts and the walls with roughness are demonstrated, which shows its potential feasibility for complex granular system simulations. [ABSTRACT FROM AUTHOR]

The forming of a porous layer of deposited nanoparticles on the heater surface is one of the unique phenomena in nucleate boiling of nanofluids. As the deposition of nanoparticles is induced by the evaporation of liquid microlayer, the average nanoparticle concentration in the microlayer is much higher than that in the bulk liquid. Therefore, the Brownian motion of nanoparticles in the microlayer may play an important role in dissipating heat from the heater surface. In this study, a new heat flux partitioning (HFP) model was proposed, in which a new heat flux component was incorporated to account for the heat transfer by nanoparticle Brownian motion in the liquid microlayer. The new heat flux component was formulated based on the latest experimental and theoretical research outcomes of microlayer evaporation. Comparison of the numerical results against the experimental data available in the literature proved that the new HFP model performs better than the classic HFP model. This study also demonstrated that the importance of nanoparticle Brownian motion is mainly controlled by the applied heat flux as it directly affects the number density of active sites on the heater surface. Finally, the effects of nanoparticle concentration, size and materials were also analyzed. [ABSTRACT FROM AUTHOR]

The dramatic boiling heat transfer performances of nanofluids have been widely attributed to the nanoparticle deposition during the boiling process. The deposited nanoparticles significantly change the microstructures and properties of the heater surface, and hence alter the characteristics of bubble nucleation and departure. Therefore, it is crucial to take into account the effects of nanoparticle deposition when modeling nucleate boiling of nanofluids using the heat flux partitioning (HFP) model (Kurul N., Podowski M.Z., 1990) [1]. In this study, new closure correlations were incorporated for the nucleate boiling parameters including the active site density, the bubble departure diameter and frequency. Parametric studies were performed through 2-D computations to analyze the effects of surface wettability enhancement, the nanoparticle material and size, respectively. The results demonstrated that through appropriate considering the modifications induced by nanoparticle deposition, the HFP model achieved a satisfactory agreement with the experimental data available in the literature, and provided a more feasible and mechanistic approach than the classic Rohsenow correlation for predicting nucleate pool boiling of nanofluids. [ABSTRACT FROM AUTHOR]

• For the solid-phase oxygen control LBE system, numerical simulations are performed for the 1:1 scale 3D UPBEAT loop. • Simulation results are in general agreement with experimental results at about 350℃ and empirical correlations at 500℃. • The mass transfer coefficient increases with the temperature and it reaches its maximum at about 475℃. The Venturi-type solid-phase oxygen control system with a bypass mass exchanger is widely regarded as an effective approach to keep the oxygen concentration in the LBE under reasonable ranges to reduce the corrosion. In this work, numerical simulations of the particle–fluid mass transfer of the oxygen concentration in LBE are performed for the 1:1 scale 3D UPBEAT loop under various conditions. The discrete element method is applied to generate the geometry of the packing of the PbO spheres. The velocity profile and oxygen concentration governing equations are solved by using the SST turbulence model. At the same temperature, the oxygen mass transfer coefficient increases monotonically with the flow rate. At the same mass flow rate, the mass transfer coefficient increases with the temperature, reaching a maximum at about 475 °C. It provides guidance for future research in the design and optimization of oxygen control systems under high temperature in lead–bismuth nuclear reactors. [ABSTRACT FROM AUTHOR]

• A force-heat transfer-analogy-based novel contact thermal resistance model is proposed. • Resembling Heat-flux by stress distribution makes free of singularity at the contact edge. • The model is validated in SC/FCC/BCC configurations and incorporated into thermal DEMs. • Appling to HTTU, temperature, ETC distributions and dynamic thermal responses are derived. • Increasing T out-wall from 200 to 1000 °C causes 20 % increase of effective thermal diffusivity. A novel particle-to-particle contact thermal resistance model is proposed in this study, based on the concept of analogy between force and heat transfer. The distribution of heat flux on the contact surface is assumed to resemble the distribution of stress, eliminating the issue of temperature singularity at the contact edge. The model is validated against existing theories and experiments, showing good agreement. The combined use of the model and the thermal discrete element method is applied to analyze temperature and effective thermal conductivity distributions in a pebble bed within a high-temperature test unit. The average effective thermal conductivity obtained from thermal conduction is found to be 2.99 and 2.61 W/(m·K) for power inputs of 20 kW and 82 kW, respectively. An increase in the outer wall temperature from 200 °C to 1000 °C results in an approximate 20 % increase in the effective thermal diffusivity. [ABSTRACT FROM AUTHOR]

Although the angular dependence of optical properties has long been recognised in transparent glazing facades, the impact of such dependence on natural ventilation between glazing has not been widely studied, especially in building facades with high solar incident angles. To better cope with such properties with the prevailing implementation of transparent building envelopes, this study investigated the effects of high solar incidence angles for vertical building facades through theoretical and numerical methods. The theoretical model validates the features of the optical properties simulated by the numerical model, supporting the numerical model's capability of revealing the radiation reflection, absorption, and transmission when multi-reflection is present. Then, such angular impact is studied with typical seasonal data in three cities, namely Shanghai, Melbourne and Chicago. Results firstly revealed the discrepancies between considering or ignoring multi-reflection between two glazing facades at varying incidence angles. Due to the opposite variation trend in reflectivity and transmissivity over angles, there is a critical solar incidence angle at 75° when multi-reflection's impact on natural ventilation reaches its highest. After that, the influence is reduced to its minimum. Identifying this angle helped highlight the enhanced natural flow due to realistic angular-dependent reflections between transparent panes, namely, under-estimation occurs if the angular dependence is not considered in the setting of optical properties. The analysis in three cities also revealed the climatic and locational impact of the angular impacts on ventilation rates. By addressing the impact on the optical and thermal performance of transparent facades, the dynamic variation of solar conditions can be more accurately integrated into passive building designs. [ABSTRACT FROM AUTHOR]

• Neural network architecture search model is applied to view factor regression of the particle-scale thermal radiation. • Deep neural networks with 3346 feasible architectures are evaluated by the HyperBand algorithm to find the optimal solution. • Trained neural architecture search model gives a good prediction of the macroscopic radiative properties in the pebble bed. In the CFD-DEM simulation of the many dense particulate systems, particle-scale thermal radiation is an important heat transfer mode under high temperatures. In this work, neural network architecture search model with different layer connection matrix is applied to the view factor regression of the thermal radiation in dense particulate systems. Deep neural networks with 3346 feasible architectures are evaluated by the HyperBand algorithm to find the local optimal solution. Neural architecture search model trained by the big data of the view factor gives a good prediction of the macroscopic radiative properties and it is in general agreement with the empirical correlations and experimental data. The particle–wall radiation decreases strongly with the distance and the maximum interaction depth is about 2.0 times the sphere diameter. The trained deep neural network model provides an efficient data-driven closure to discuss the thermal radiation of the particle–particle and particle–wall interactions in particle bed. [ABSTRACT FROM AUTHOR]

A particle-scale surface tension force model (STF) is proposed here to be incorporated in the smoothed hydrodynamics particle (SPH) method. This model is based on the identification of interface geometry and the gradient of densities across the interface. A square bubble of single-phase and a square bubble immersed in fluids are simulated by the STF model accompanied with a combined kernel in SPH to validate their suitability to simulate the immersed bubble motion. Two cases of rising bubbles, i.e., a single rising bubble and a pair of rising bubbles, are simulated for demonstration. The rising velocity, density, surface tension force, interfacial curvature, the power of the STF, and the smoothing length of the rising bubble and surrounding fluids are all computed by the current STF model to study the characteristics of immersed bubble's motion and coalescence. The current model provides a way to capture the interfacial interactions in two-phase flows at particle scales. [ABSTRACT FROM AUTHOR]

A key issue in pulmonary drug delivery is improving the medical delivery device for effective and targeted treatment. Spacers are clear plastic containers attached to inhalers aimed at delivering more drug particles to the respiratory tract. The spacer's one-way valve plays an important role in controlling and initializing the particles into the oral cavity. This article studied particle inhalation and deposition in an idealized oral airway geometry to better optimize the spacer one-way valve shape and design. Three steady flow rates were used 15, 30, and 60 l/min and a Lagrangian, one-way coupling particle tracking model with near-wall turbulence fluctuation correction was used to determine the deposition rates. For all three breathing rates, the velocity field in the midsagittal plane showed similar gross fluid dynamics characteristics, such as the separation and recirculation regions that occur after the larynx. The particle deposition rates compared reasonably well with available experiments. Most particles deposited at the larynx, where the airway has a decreasing cross-sectional area. For different particles sizes, most particles introduced at the lower region of the mouth show higher possibility to pass through upper airway and enter the trachea and lung airways. The particle deposition patterns in the airway were traced back to their initial inlet position at the oral inlet; and this information provides the background for a conceptual and optimized design of the spacer one-way valve. Copyright 2015 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

The flow characteristics of a gravity-driven dense granular flow in a granular bed with a contracted drainage orifice are studied by using discrete element method and quantitative analysis. Three values of discharging rates, ranging from fast to slow dense flows, are investigated. Time variations and derivatives of mean forces and velocities, as well as their respective correlations, are analyzed to quantitatively depict the characteristics of granular flow as well as flow regime categorization. The auto-correlation functions, as well as their Fourier spectrums, are utilized to characterize the differences between the mechanisms of slow and fast granular flows. Finally, it is suggested that the flow regimes of slow and fast flows can be characterized by the kinetic and kinematic flow properties of particles. [ABSTRACT FROM AUTHOR]

Abstract: Flow over an open side window in a car exhibits similar characteristics as the flow over an open cavity. Computational Fluid Dynamics (CFD) simulation over a cavity was done as a benchmark. The unsteady flow simulation was carried out using Scale Adaptive Simulation (SAS) turbulence model. The benchmark results, frequency and sound pressure levels of feedback and resonance modes, all well matched with the experimental data. Then, with the right rear window, for example, the mechanism of the side window buffeting was investigated. The simulation results show that side window buffeting noise is generated by large scale vortices and in low frequency. Furthermore, buffeting noise characteristics under several patterns of side windows opening were also numerically investigated. As a result, rear window buffeting noise is more severe than that of front window when one window open, and combination pattern of side windows open can reduce buffeting noise. To decrease the interior noise and improve car ride comfort, four suppression measures through adding a side window weather deflector at the A-pillars, constructing a cavity at the B-pillars, combination of the front and rear windows and installing a row of square cylinder deflector at the B-pillars were also studied, respectively. In conclusion, certain noise reduction can be achieved through four passive control methods. [Copyright &y& Elsevier]

Highlights: [•] Pebble flow uniformity and stagnation characteristics are very important for HTR-PM. [•] Arc- and brachistochrone-shaped configuration effects are studied by DEM simulation. [•] Best bed configurations with uniform flow and no stagnated pebbles are suggested. [•] Detailed quantified characteristics of bed configuration effects are shown for explanation. [Copyright &y& Elsevier]

Highlights: [•] We show a detailed analysis of void fraction (VF) in HTR-10 of China using DEM. [•] Radial distribution (RD) of VF is uniform in the core and oscillated near the wall. [•] Axial distribution (AD) is linearly varied along height due to effect of gravity. [•] Steady RD of VF in the conical base is Gaussian-like, larger than packing bed. [•] Joint linear and normal distribution of VF is analyzed and explained. [Copyright &y& Elsevier]