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The capillary aerosol generator (CAG) is operated with the principal of thermal liquid evaporation through heating of e-liquid in the initial phase, followed by nucleation and condensation regulated through a mixture of airflow to generate aerosols, such as in an electronic cigarette (EC). The CAG is particularly useful in generating aerosols of large volumes in a continuous manner, for instances such as in vivo inhalation toxicology studies, where usage of ECs is not feasible. The thermal effects of generating aerosol from the CAG are similar in terms of temperature applied in an EC, thus allowing investigators to assess the vapors of e-liquids at scale and reproducibility. As the operation of the CAG allows users to control critical parameters such as the flow rate of e-liquid, heating temperatures and dilution air flows, it allows investigators to test various e-liquid formulations in a well-controlled device. Properties, such as aerosol particle size, are demonstrated to be regulated with the air flow rate with respect to the e-liquid flow and e-liquid composition. The CAG, however, is limited in assessing common EC-related issues, such as overheating of its elements. We seek to demonstrate that the CAG can generate aerosol that is reproducible and continuous, by assessing the chemical and physical aerosol characteristics with a chosen e-liquid formulation. The protocol describes the operating parameters of liquid flow rate, dilution air-flow rates and operating procedures needing to optimize the aerosol concentration and particle size required for an in vivo toxicology study. Presenting the representative results from the protocol and discussing the challenges and applications of working with a CAG, we demonstrate that CAG can be used in a reproducible fashion. The technology and protocol, that has been developed from prior work, serve as a foundation for future innovations for laboratory-controlled aerosol generation investigations.

Inhalation exposure chambers may be used for in vivo drug delivery or toxicological assessments among other applications. Nose-only exposure chamber (NOEC) systems limit non-respiratory aerosol exposure pathways that may affect biological response analyses in mice. Uniform aerosol delivery between all ports is desired, but any exposure system design may introduce variability. The aerosol flow characteristics in a commercially available NOEC system were assessed computationally and experimentally to estimate the particle size-dependent non-uniformities of the aerosol sampled at each exposure port. Only dilute non-evolving aerosols are considered in the present study. The experimental measurements recorded a flow velocity variability of up to 20% between ports. Sampling variability between ports was experimentally verified to be within 10% for particles >0.56 µm and 3 µm) was observed inside the ports, causing visible aerosol separation on the top of the channel delivering the aerosol to the exposure trumpet. As the effect was minor and applied to particles beyond the size range recommended for mouse inhalation studies, it should have no influence on the dosimetry of inhaled aerosols. In the range of aerosol particle sizes and flow rates considered, a good agreement between computational and experimental results was found, confirming the suitability of the system for mouse inhalation studies, and the insights obtained may give rise to further improvements in the system design. Copyright © 2019 American Association for Aerosol Research

Chemical and physical characterization of transported evolving aerosols in an in vitro system is complex. The challenges include appropriate sampling sensitivity, measurement capabilities, and performing online measurements of constituents in the flowing aerosol during exposure. We assessed the performance of single-photon ionization mass spectrometry in measuring aerosol properties within an in vitro aerosol exposure system. The sampling efficiency of the instrument was studied under three protocols to capture the evolving aerosol process inside the exposure system, and it was evaluated using computational fluid dynamics modeling. The changes in the aerosol as dilution is applied show not only a reduction in concentration of the traced substances but also selective sampling due to evolution of the aerosol and (gas/liquid) phase partitioning of the substances forming the aerosol or a change in the aerosol properties. These effects have potentially a direct impact on the delivered dose, as aerosol deposition is dependent on particle size. Dilution affects the chemical concentration of the substances as well as the interconnected physical properties of the aerosol; therefore, the experimental design of in vitro studies should not only report the dilution flow rates but also details of the applied dilution protocol. This adds a layer of complexity to the design and comparison of studies. We also discuss the potential and limitations of single-photon ionization mass spectrometry as a tool in in vitro monitoring of aerosols.

A key to understanding biological response due to cell exposure to chemical constituents in aerosols is to accurately be able to determine the delivered dose. Deposition efficiency and uniformity of deposition was measured experimentally in the Vitrocell® 24/48 air–liquid-interface (ALI) in vitro exposure system using monodisperse solid fluorescent particles with mass median aerodynamic diameters (MMAD) of 0.51, 1.1, 2.2 and 3.3 µm. Experimental results were compared with computational fluid dynamics (CFD; using both Lagrangian and Eulerian approaches) predicted deposition efficiency and uniformity for a single row (N = 6) of cell culture inserts in the Vitrocell® 24/48 system. Deposited fluorescent monodisperse particles were quantified using fluorescent microscopy and Image J software. Experiments were conducted using a suspension of two particle MMADs with each experiment being conducted a total of three times on different days. The average experimentally measured deposition efficiency ranged from a low of 0.013% for 0.51 µm MMAD particles to a maximum 0.86% for 3.3 µm MMAD particles. There was good agreement between the average experimentally measured and the CFD predicted particle deposition efficiency (regardless of approach) with agreement being slightly better at the smaller MMADs. Experimentally measured and CFD predicted average uniformity of deposition was >45% of the mean and within 15% of the mean for 0.51 µm and 2.2 MMAD µm particles, respectively. Experimentally measured average uniformity of deposition was between 15 and 45% of the mean while CFD predictions were within 15% of the mean for 1.1 and 3.3 µm MMAD particles. The deposition efficiency and uniformity across the cell culture inserts for solid particles should be considered when designing exposure regimens using the Vitrocell® 24/48 ALI in vitro exposure system. Copyright © 2019 American Association for Aerosol Research

Many aerosols present in nature (e.g., atmosphere) or artificially generated for various purposes (e.g., inhalation) are composed of liquids that are prone to continuous evolution due to thermodynamical changes of surrounding conditions as for example temperature and humidity. Thermodynamical changes influence the aerosol dynamics causing condensation or evaporation and subsequent aerosol size growth or shrinkage. These evolution mechanisms simultaneously influence the aerosol deposition due to particle size dependent nature of the aerosol deposition mechanisms (i.e., inertial and diffusional deposition). As the experimental measurements of evolving liquid aerosol deposition are challenging, development and validation of computational models allowing aerosol simulations are important to explore and understand the underlying physics. In this manuscript, we present our multispecies evaporation/condensation model implemented in an Eulerian aerosol framework. The model is validated by comparing with the available literature data for droplet evaporation/condensation under controlled conditions. We applied the model to explore the effect of the temperature and humidity variations on the aerosol size change and its consequent influence on the aerosol deposition in a bent pipe for single- and multispecies mixtures. We show influence of condensation on the aerosol deposition efficiency for various particle sizes. Our results demonstrate that particle size growth favoring inertial deposition and inhibiting diffusional deposition can significantly influence the number of depositing particles and result in an increase of the deposited liquid mass on the walls. These effects are caused by subtle interaction of flowing aerosols in the laminar boundary layer with surrounding vapors available for condensation and they are dependent on the gradient of temperature between flowing mixture and walls.

Cigarette smoking is one major modifiable risk factor in the development and progression of chronic obstructive pulmonary disease and cardiovascular disease. To characterize and compare cigarette smoke (CS)‐induced disease endpoints after exposure in either whole‐body (WB) or nose‐only (NO) exposure systems, we exposed apolipoprotein E‐deficient mice to filtered air (Sham) or to the same total particulate matter (TPM) concentration of mainstream smoke from 3R4F reference cigarettes in NO or WB exposure chambers (EC) for 2 months. At matching TPM concentrations, we observed similar concentrations of carbon monoxide, acetaldehyde, and acrolein, but higher concentrations of nicotine and formaldehyde in NOEC than in WBEC. In both exposure systems, CS exposure led to the expected adaptive changes in nasal epithelia, altered lung function, lung inflammation, and pronounced changes in the nasal epithelial transcriptome and lung proteome. Exposure in the NOEC caused generally more severe histopathological changes in the nasal epithelia and a higher stress response as indicated by body weight decrease and lower blood lymphocyte counts compared with WB exposed mice. Erythropoiesis, and increases in total plasma triglyceride levels and atherosclerotic plaque area were observed only in CS‐exposed mice in the WBEC group but not in the NOEC group. Although the composition of CS in the breathing zone is not completely comparable in the two exposure systems, the CS‐induced respiratory disease endpoints were largely confirmed in both systems, with a higher magnitude of severity after NO exposure. CS‐accelerated atherosclerosis and other pro‐atherosclerotic factors were only significant in WBEC., To characterize and compare cigarette smoke‐induced disease endpoints after exposure in either whole‐body (WB) or nose‐only (NO) exposure chambers (EC), we exposed apolipoprotein E‐deficient mice to filtered air or mainstream smoke from 3R4F reference cigarettes (same target total particulate matter concentration) in NOEC or WBEC for 2 months. The main respiratory disease endpoints and exposure effects were confirmed in both systems, with a greater severity in the NOEC group. Exposure in the WBEC caused generally a more pronounced cardiovascular response.

The aerosols generated by most electronic nicotine delivery products including electrically heated tobacco products and e-vapor products, consist of fine (micrometer to submicrometer size) liquid particles suspended in a gas phase. The inhalation of aerosols involves complex interactions of airflow, dynamic evolution in the aerosol, and interaction with the surfaces of the airways and lungs, which, together, determine the amount of inhaled material that deposits locally. Physical processes, such as evaporation, condensation, and coagulation, are constantly changing the conditions of transport and deposition of the chemical species in the complex mixture of aerosol constituents. These aerosol's physical properties are modulated by the geometric and physiological factors of the inhalation and exhalation phases of the breathing process. The parameters of the resulting exposure dose will be described, as well as the challenges of dose extrapolations from machine-generated aerosol exposure of in vitro models and experimental animals to human exposure.

Aerosol dosimetry estimates for mouse strains used as models for human disease are not available, primarily because of the lack of tracheobronchial airway morphometry data. By using micro‐CT scans of in‐situ prepared lung casts, tracheobronchial airway morphometry for four strains of mice were obtained: Balb/c, AJ, C57BL/6, and Apoe−/−. The automated tracheobronchial airway morphometry algorithms for airway length and diameter were successfully verified against previously published manual and automated tracheobronchial airway morphometry data derived from two identical in‐situ Balb/c mouse lung casts. There was also excellent agreement in tracheobronchial airway length and diameter between the automated and manual airway data for the AJ, C57BL/6, and Apoe−/− mice. Differences in branch angle measurements were partially due to the differences in definition between the automated algorithms and manual morphometry techniques. Unlike the manual airway morphometry techniques, the automated algorithms were able to provide a value for inclination to gravity for each airway. Inclusion of an inclination to gravity angle for each airway along with airway length, diameter, and branch angle make the current automated tracheobronchial airway data suitable for use in dosimetry programs that can provide dosimetry estimates for inhaled material. The significant differences in upper tracheobronchial airways between Balb/c mice and between C57BL/6 and Apoe−/− mice highlight the need for mouse strain‐specific aerosol dosimetry estimates.

Chemical and physical characterization of transported evolving aerosols in an

Computational modeling of multispecies aerosols generated from nucleating supersaturated vapors is a challenging task because of the complexity of the involved thermodynamic phenomena, non-existing validated and/or first principles-based models for the nucleation and condensation/evaporation processes, necessity for high computational effort, and, finally, lack of simulation data and software for validation. Here, we present our contribution towards tackling at least some of these challenges by developing AeroSolved, a publicly available open-source computational fluid dynamics code for simulation of multispecies evolving aerosols in an Eulerian framework. We present a consistent modeling approach to nucleation and condensation using a multispecies extension of the classical nucleation theory and a multispecies Stefan flow model for particle condensation, respectively. The internally mixed assumption is used, i.e., the species concentration partitioning is particle size independent and uniform across local particle size distribution. Instantaneous temperature equlibration is also assumed between the phases. Applied assumptions were tested for aerosol flows with mean diameter particle size in the range of micrometers. Applications beyond tested regimes (e.g., nanometer or sub-millimeter particle size ranges, thermodynamical) would need revisiting the assumptions and consequently modeling limitations with required inclusion of additional processes (e.g., Kelvin effect, Fuchs–Sutugin corrections or Marangoni flows influence). The developed computational models are tested in three separate scenarios simulating: uniform nucleation/condensation conditions, single-particle evaporation/condensation, and laminar flow diffusion chamber flows. Two distinct approaches are proposed to solve the population balance equation and calculate the particle size distribution. The moment method assumes a log-normal shape and fixed width of distribution, while the sectional method resolves the particle size distribution without constraints on its shape, thus being more accurate but also computationally expensive. These two methods are demonstrated as complementary tools for industrial real-case scenarios where complex aerosol flow is simulated in a simplified geometry of the capillary aerosol generator. The more accurate and detailed sectional method serves as a tuning tool for the less computationally demanding log-normal moment method, which is then practically used for parametric studies concerning system performance. The simulations presented here unravel details on particle formation and the sensitivity of the setup to thermodynamic conditions and pave the road towards engineering application of the developed methods.

Accurately determining the delivered dose is critical to understanding biological response due to cell exposure to chemical constituents in aerosols. Deposition efficiency and uniformity of deposition was measured experimentally using monodisperse solid fluorescent particles with mass median aerodynamic diameters (MMAD) of 0.51, 1.1, 2.2 and 3.3 μm in the Vitrocell® AMES 48 air-liquid-interface (ALI) in vitro exposure system. Experimental results were compared with computational fluid dynamic, (CFD; using both Lagrangian and Eulerian approaches) predicted deposition efficiency and uniformity for a single row (N = 6) of petri dishes in the Vitrocell® AMES 48 system. The average experimentally measured deposition efficiency ranged from 0.007% to 0.43% for 0.51–3.3 μm MMAD particles, respectively. There was good agreement between average experimentally measured and the CFD predicted particle deposition efficiency, regardless of approach. Experimentally measured and CFD predicted average uniformity of deposition was greater than 45% of the mean for all particle diameters. During this work a new design was introduced by the manufacturer and evaluated using Lagragian CFD. Lagragian CFD predictions showed better uniformity of deposition, but reduced deposition efficiency with the new design. Deposition efficiency and variability in particle deposition across petri dishes for solid particles should be considered when designing exposure regimens using the Vitrocell® AMES 48 ALI in vitro exposure system.

Open cell foams are considered promising catalytic substrates providing high surface area and a tortuous structure resulting in enhanced mass transfer characteristics. CFD analysis, recently, has focused in pointing structures with favourable reactivity-flow resistance characteristics. In order to reduce the geometrical complexity and computational efforts, foams have been modelled as regular (polyhedric) open cell structures. In this study a comprehensive comparison of real foams with equivalent Kelvin cell lattices is performed in CFD. Therefore 4 typical foams (two ceramic and two metallic) have been chosen. Geometric properties have been accessed with Micro-Tomography scans. Randomised Kelvin cell lattices have been generated matching porosity and specific surface area of the scanned real foams. Geometric, momentum and mass transfer characteristics of real foams and Kelvin cell lattices are analysed with CFD. Kelvin cell lattices showed similar behaviour in respect to their real foam equivalents, had though clearly better reactivity-pressure drop trade-offs. Based on the results presented best performances as a catalyst can be expected by 3D printed, additive manufactured, high porosity polyhedric structures.

Accurate predictions of aerosol transport, evolution, and deposition in the human airways are crucial for inhalation dosimetry investigations. Inhaled aerosol transported through the airways undergoes thermodynamic changes due to changes in temperature and humidity. Aerosol evolution processes are particularly important for liquid multispecies aerosols. These aerosols are sensitive to condensation and/or evaporation dynamics, which can modify gas/liquid partitioning of each species and particle size distribution. In this manuscript, we present computational fluid dynamics simulations of complex aerosol mixtures in a realistic geometry of the human respiratory tract cast model. We used a publicly available computational framework, AeroSolved, developed for simulation of evolving multispecies aerosol mixtures. We evaluated the dynamics of liquid particles in physiologically relevant conditions of 100 % relative humidity at the temperature of 37 ° C . We studied two separate inhalation flow scenarios: in the first case, a warm aerosol at 50 ° C was inhaled and subsequently cooled down while flowing in the airways. In the second case, an aerosol at room temperature was inhaled and heated up to the temperature of 37 ° C . Our results demonstrated that aerosol evolution mainly occurs in the upper segments of the airways (throat and trachea) at the very short timescales. Apart from showing the significant influence of temperature and humidity conditions on aerosol dynamics and evolution, we also measured aerosol deposition fluxes investigating the dependence of the delivered aerosol mass on evolution mechanisms. We showed that the delivered regional mass of each species depends on the physico-chemical properties of the mixture, and it is also significantly influenced by the airways’ humidity and thermal conditions. It was also shown that the species-specific properties of the liquid mixture (e.g., activity coefficient) play an important role in gas/liquid partitioning of the species. With AeroSolved such dependencies can be further investigated with greater attention towards specific needs and physiologically important conditions (e.g., transient flow inhalation patterns, aerosol mixture composition and its properties).

Foam based catalytic converters have the potential to decrease cold-start emissions in automotive applications due to their low thermal inertia and excellent mass and heat transfer properties. A 3D CFD model of a foam based catalytic converter is proposed and employed here to simulate cold-start transients. The modeled phenomena include conjugate heat transfer, finite rate washcoat diffusion and detailed multi-step chemistry of CO oxidation over Pt. The simulation results confirm that foam based catalytic reactors have potentially lower cold start emissions compared to honeycomb reactors. Cumulative emissions decrease with increasing foam porosity, decreasing pore diameter and decreasing effective axial solid conductivity. The effects of inflow velocity, inflow CO mass fraction and washcoat surface area (Pt loading) on cold start emissions are discussed in detail. The effects of foam properties and inflow conditions on cumulative emissions are summarized with a correlation that matches the results of the pore scale simulations.

Multi-well aerosol exposure systems are used in modern toxicology assessment studies to deliver aerosol to a large number of tissue/cell culture samples simultaneously. These systems are designed to control the experimental conditions of a delivered aerosol. In these systems (e.g., those developed by Vitrocell GmbH), the aerosol mixture is delivered perpendicularly to the tissue culture through a trumpet-shaped (flared) pipe. In the well chamber where the tissue/cell culture is exposed, the flow is smooth and laminar, which limits shear forces and potential moisture loss that may damage the tissue/cells. These operating flow conditions also determine the aerosol dynamics and deposition mechanisms within the system. The utility of these systems to evaluate biological responses depends on the quantity of tissue culture. With limited experimental data, evaluating the aerosol deposition via computational means is necessary to predict the deposition efficiency. For our investigations, we employed a recently developed Eulerian Computational Fluid Dynamics solver (available at www.aerosolved.com ) for simulations of polydisperse multi-species aerosol transport and deposition. We investigated deposition efficiency using various exposure distances to the tissue culture, aerosol properties, and operating conditions. Terms associated with drag, gravitation, and Brownian diffusion were included in the aerosol equations to predict the deposition of the polydisperse aerosol. Results were verified by comparisons with the available experimental data, and predictions were obtained from the Lagrangian simulations using commercially available software. Within the recommended operating conditions, inertial impaction was found not to affect aerosol deposition, which is driven mainly by the size-dependent sedimentation and diffusion mechanisms. An important implication is that for a wide range of droplet sizes, the delivered dose to the tissue is independent of sampled flow rate. Taking this into account, a simple and robust size-dependent theoretical model of the aerosol deposition efficiency was developed. This theoretical model is based on aerosol characteristics, flow, and geometry inputs without the use of any fitting parameter. It can be applied to various exposure system geometries under different operating conditions, as verified in comparisons with published deposition efficiency data obtained from experiments and computations.

Catalyst technologies for automotive after-treatment systems require constant developments to comply with the latest regulations concerning real driving emissions. Apart from the current benchmark in catalyst substrates of honeycombs (HCs), the research is focusing on open cell structures, which show promising properties [1]. The network of solid struts of the open cell lattices overcomes the limits of laminar flow in HCs and enhances higher conversion efficiencies [2][3], lower cold start emissions and higher flow uniformity, which is a key factor for catalyst durability [4][5][6][7]. Open cells allow more flexibility in the geometrical configuration of the reactor [8], but they show also a higher pressure drop per unit of length [9][10], decreasing engine efficiency. Thus, to have a fair comparison between HC and open cells, the performance index I has been introduced [2], which evaluates catalyst efficiency by weighting conversion and pressure drop. CFD analysis suggested that the trade off is in favour of open cell structures when the porosity is high enough [11][1]. Here open cells are studied as regular polyhedral structures, which literature have shown to be more performant than randomized foams [12]. Several works conducted numerical analysis of open cell foams consisting of regular cells [2] [13] [14]. Regular structures are easier to handle because they require only two parameters (for example the characteristic pore dimension and its ratio with the strut diameter) to be defined and mathematical expressions allow the derivation all the other geometrical properties [1]. Often the Kelvin cell has been used as a typical elementary cell.

Background and Objectives. Breast-conserving surgery represents the standard of care for the treatment of small breast cancers. However, there is a population of patients who cannot undergo the standard surgical procedures due to several reasons such as age, performance status, or comorbidity. Our aim was to investigate the feasibility and safety of percutaneous US-guided laser ablation for unresectable unifocal breast cancer (BC). Methods. Between December 2012 and March 2017, 12 consecutive patients underwent percutaneous US-guided laser ablation as radical treatment of primary inoperable unifocal BC. Results. At median follow-up of 28.5 months (range 6-51), no residual disease or progression occurred; the overall success rate for complete tumor ablation was therefore 100%. No significant operative side effects were observed, with only 2 (13.3%) experiencing slight to mild pain during the procedure, and all patients complained of a mild dull aching pain in the first week after procedure. Conclusions. Laser ablation promises to be a safe and feasible approach in those patients who are not eligible to the standard surgical approach. However, longer follow-up results and larger studies are strongly needed.

Polyhedral open cell lattice catalyst substrates are proposed based on results of numerical simulations and recent advances in Additive Manufacturing (AM) techniques. Detailed simulations have compared different polyhedral structures in terms of mass transfer (aiming at optimal reactivity in the mass transfer limited domain) and flow through resistance. The simulations have taken into account dimensional limits given by the possibilities of AM techniques. Comparisons with state of art honeycombs have also been used in order to identify the optimal shape. Substrates with these optimal characteristics have been manufactured out of Al2O3 with Stereolithography. Subsequently, these substrates have been coated and used for measurements of C3H6 oxidation in a model gas reactor. Measurements have focused in determining oxidation efficiency at different gas hourly space velocities as well as light-off behaviour. Simulation results show that the optimal open cell structures are comprised by a cubic elementary cell rotated by 45° so that one spatial diagonal of the cube is aligned to the main gas flow. Higher porosities and smaller strut diameters improve the reactivity to pressure drop trade off. However, given the current manufacturing limitations, it is not possible to produce structures with strut diameter lower than 0.5 mm. This results in high porosity but low specific surface area (i.e. e = 0.95 and Sv = 400 m2/m3). Thus, reaching a target conversion requires higher overall catalyst volume. The simulations show that for a series of geometrical parameters the open cell structures can reach identical conversion in respect to the honeycombs with only a fraction of the overall surface area and thus a fraction of the noble metals, while the overall dimensions are in the same order of magnitude and the pressure drop can reach lower levels. Measurements in the model gas reactor confirm the mass transfer advantages of the polyhedral structures as predicted by the simulations. Measurements also show that the polyhedral lattices have very similar light-off behaviour in spite the four times lower surface area.

Foam based catalytic converters are a promising alternative to the established honeycomb reactors for treatment of pollutants in automotive applications. They provide excellent mass transfer properties at reasonable pressure drop and have the potential to achieve high conversion at smaller external dimensions. The goal of this work is to determine the relative importance of washcoat diffusion resistance in foam based reactors. Catalytic oxidation of CO over Pt is computationally simulated with a volume averaged model. Based on micro-kinetic modelling and the resulting resolution of the reaction-diffusion processes inside the washcoat, the simulations provide a comprehensive picture of the chemistry and transport processes. Washcoat diffusion resistances in foams – although often considered negligible – are shown to be at least as important as in honeycomb converters, due to the higher external mass transfer coefficients in foams. The computations show a reduction in conversion with respect to the limit of infinitely fast kinetics of 46% for the foam-based reactor after catalytic light-off. The impact of washcoat diffusion resistance on conversion decreases with increasing surface area of the washcoat. An increase in pore size of the washcoat leads to improved conversion.

Pore-scale simulations of transport phenomena in foam based catalytic converters are highly desirable due to their intrinsic accuracy in describing the involved physics. Unfortunately, such computations are prohibitively time consuming and costly. Here we combine a detailed pore-scale characterization with a volume average description of an open-cell foam based catalytic converter. The resulting volume averaged model is accurate and more than three orders of magnitude more efficient in terms of computational time, compared to direct pore scale simulations. This makes simulations of the related complex phenomena tractable, providing a highly flexible and powerful tool for parametric studies of open-cell foams. The volume-averaged model is validated with a pore-scale simulation of a full-scale catalytic converter used for automotive exhaust gas treatment. Fast chemistry is assumed and the heat released by the chemical reaction in combination with conjugate heat transfer is considered. We show that the conversion to pressure drop trade-off improves with increasing foam porosity and the heat release of the reaction significantly affects the pressure drop across the reactor. The simulations show non-uniform surface temperatures which are attributed to the non-unity Lewis number of the mass transfer limiting species. The model predictions agree well with experimental measurements of pressure drop and Sherwood number in open-cell foams.

We study, numerically and analytically, the relationship between the Eulerian spectrum of kinetic energy, E E(k, t), in isotropic turbulence and the corresponding Lagrangian frequency energy spectrum, E L(ω, t), for which we derive an evolution equation. Our DNS results show that not only E L(ω, t) but also the Lagrangian frequency spectrum of the dissipation rate $${\varepsilon_{\rm L} (\omega, t)}$$ has its maximum at low frequencies (about the turnover frequency of energy-containing eddies) and decays exponentially at large frequencies ω (about a half of the Kolmogorov microscale frequency) for both stationary and decaying isotropic turbulence. Our main analytical result is the derivation of equations that bridge the Eulerian and Lagrangian spectra and allow the determination of the Lagrangian spectrum, E L (ω) for a given Eulerian spectrum, E E (k), as well as the Lagrangian dissipation, $${\varepsilon_{\rm L}(\omega)}$$ , for a given Eulerian counterpart, $${\varepsilon_{\rm E} (k)=2\nu k^2 E_{\rm E}(k)}$$ . These equations were derived from the Navier–Stokes equations in the sweeping-free coordinate system (intermediate between the Eulerian and Lagrangian frameworks) which eliminates the effect of the kinematic sweeping of the small eddies by the larger eddies. We show that both analytical relationships between E L (ω) and E E (k) and between $${\varepsilon_{\rm L} (\omega)}$$ and $${\varepsilon_{\rm E} (k)}$$ are in very good quantitative agreement with our DNS results and explain how $${\varepsilon_{\rm L} (\omega, t)}$$ has its maximum at low frequencies and decays exponentially at large frequencies.

Today restrictions on pollutant emissions are forcing more and more the use of catalystbased after-treatment systems both in SI and in Diesel engines. The application of monolith cores with a honeycomb structure is an established practice: however, to overcome drawbacks such as poor flow homogenization, the use of ceramic foams has been recently investigated [1,2,3] as an alternative showing better conversion efficiencies (even if with higher pressure losses).

This study investigates the two-way coupling effects of finite-size solid spherical particles on decaying isotropic turbulence using direct numerical simulation with an immersed boundary method. We fully resolve all the relevant scales of turbulence around freely moving particles of the Taylor length-scale size, 1.2≤d/λ≤2.6. The particle diameter and Stokes number in terms of Kolmogorov length- and time scales are 16≤d/η≤35 and 38≤τp/τk≤178, respectively, at the time the particles are released in the flow. The particles mass fraction range is 0.026≤φm≤1.0, corresponding to a volume fraction of 0.01≤φv≤0.1 and density ratio of 2.56≤ρp/ρf≤10. The maximum number of dispersed particles is 6400 for φv=0.1. The typical particle Reynolds number is of O(10). The effects of the particles on the temporal development of turbulence kinetic energy E(t), its dissipation rate (t), its two-way coupling rate of change Ψp(t) and frequency spectra E(ω) are discussed.In contrast to particles with d < η, the effect of the particles in this study, with d > η, is that E(t) is always smaller than that of the single-phase flow. In addition, Ψp(t) is always positive for particles with d > η, whereas it can be positive or negative for particles with d < η.

In this work, we employ direct numerical simulation of turbulence one-way coupled to Lagrangian tracking to investigate microbubble distribution in upward and downward channel flow. We consider a closed channel flow at Re = 150 and a dispersion of microbubbles characterized by a diameter of 220m. Bubbles are assumed contaminated by surfactants (i.e., no-slip condition at bubble surface) and are subject to drag, gravity, pressure gradient forces, Basset history force and aerodynamic lift. Our results confirm previous findings and show that microbubble dispersion in the wall region is dominated by the action of gravity combined with the lift force. Specifically, in upward flow, bubble rising velocity in the wall region generates a lift force which pushes bubbles to the wall. In downward flow, bubble rising velocity against the fluid generates a lift force which prevents microbubbles from reaching the viscous sublayer. In the wall region, we observe bubble preferential segregation in high-speed regions in the downflow case, and non-preferential distribution in the upflow case. This phenomenon is related to the effect of the lift force. Compared to experiments, the current lift force model produces larger consequences, this effect being overemphasized in the upflow case in which a large number of bubbles is segregated near the wall. In this case, the resulting bubble wall-peak of concentration outranges experimental results. These results, so deeply related to the lift force, underline the crucial role of current understanding of the fluid forces acting on bubbles and help to formulate questions about available force models, bubble–bubble interactions and two-way coupling which can be crucial for accurate predictions in the region very near the wall. 2005 Elsevier Ltd. All rights reserved.

Open cell foams are attractive materials for various industrial applications, but building accurate universal correlations is challenging due to their great geometrical complexity. Momentum and mass transfer of a randomly packed Kelvin cell structures are numerically investigated. Porosity, e, Kelvin cell size, PPI, and inflow velocity, u, are systematically varied for a total of 120 simulations. Correlations for geometrical and transfer properties are discussed. The analogy based on the generalized Leveque equation (Martin, 2002) between mass and momentum transfer is evaluated and it is qualitatively in agreement with the results of Incera Garrido et al. (2008) on ceramic foams.

[1] Ground-based measurements of stratospheric constituents were carried out from Thule Air Base, Greenland (76.5°N, 68.7°W), during the winters of 2001–2002 and 2002–2003, involving operation of a millimeter-wave spectrometer (GBMS) and a lidar system. This work focuses on the GBMS retrievals of stratospheric O3, CO, N2O, and HNO3, and on lidar stratospheric temperature data obtained during the first of the two winter campaigns, from mid-January to early March 2002. For the Arctic lower stratosphere, the winter 2001–2002 is one of the warmest winters on record. During a large fraction of the winter, the vortex was weakened by the influence of the Aleutian high, with low ozone concentrations and high temperatures observed by GBMS and lidar above ∼27 km during the second half of February and in early March. At 900 K (∼32 km altitude), the low ozone concentrations observed by GBMS in the Aleutian high are shown to be well correlated to low solar exposure. Throughout the winter, PSCs were rarely observed by POAM III, and the last detection was recorded on 17 January. During the lidar and GBMS observing period that followed, stratospheric temperatures remained above the threshold for PSCs formation throughout the vortex. Nonetheless, using correlations between GBMS O3 and N2O mixing ratios, in early February a large ozone deficiency owing to local ozone loss is noted inside the vortex. GBMS O3-N2O correlations suggest that isentropic transport brought a O3 deficit also to regions near the vortex edge, where transport most likely mimicked local ozone loss.

It has been established both numerically and experimentally [see, e.g., A. Ferrante and S. E. Elghobashi, “On the physical mechanisms of two-way coupling in particle-laden isotropic turbulence,” Phys. Fluids 15, 315 (2003); T. S. Yang and S. S. Shy, “Two-way interaction between solid particles and homogeneous air turbulence: Particle settling rate and turbulence modification measurements,” J. Fluid Mech. 526, 171 (2005)] that the Stokes number, τp/τk, can be used as an indicator to determine the extent to which small particles (dp