Evolution Of Size Distribution Research Articles

Dust diffusion in SPH simulations of an isolated galaxy

ABSTRACT We compute the evolution of the grain size distribution (GSD) in a suite of numerical simulations of an isolated Milky Way-like galaxy using the N-body/smoothed-particle-hydrodynamics code gadget4-osaka. The full GSD is sampled on a logarithmically spaced grid with 30 bins, and its evolution is calculated self-consistently with the hydrodynamical and chemical evolution of the galaxy using a state-of-the-art star formation and feedback model. In previous versions of this model, the GSD tended to be slightly biased towards larger grains and the extinction curve had a tendency to be flatter than the observations. This work addresses these issues by considering the diffusion of dust and metals through turbulence on subgrid scales and introducing a multiphase subgrid model that enables a smoother transition from diffuse to dense gas. We show that diffusion can significantly enhance the production of small grains and improve the agreement with the observed dust extinction curve in the Milky Way.

The co-evolution of molecular hydrogen and the grain size distribution in an isolated galaxy

ABSTRACT Understanding the evolution of dust and molecular hydrogen (H2) is a critical aspect of galaxy evolution, as they affect star formation and the spectral energy distribution of galaxies. We use the N-body/smoothed particle hydrodynamics code gadget4-osaka to compute the evolution of dust and H2 in a suite of numerical simulations of an isolated Milky Way-like galaxy. The evolution of the full grain size distribution (GSD) is solved by sampling the grain size on a logarithmically spaced grid with 30 bins. The evolution of a primordial chemistry network with 12 species is solved consistently with the hydrodynamic evolution of the system, including star formation, metal and energy ejections from stars into the interstellar medium through supernova feedback, and stellar winds. The formation model for H2 considers the GSD and photodissociation through the UV radiation of young stars. We identify the processes needed for producing a sizeable amount of H2, verify that the resulting star formation law in the later stages of galaxy evolution is consistent with observations of local spirals, and show that our model manages to produce a galactic molecular gas fraction in line with observations of Milky Way-like galaxies. We stress the importance of the co-evolution of the GSD and H2, as models assuming a fixed MRN shape for the GSD overestimate the production of H2 in regimes where the dust abundance is dominated by large grains and underestimate it in the regime where the dust is dominated by small grains, both of which are realized in simulations of dust evolution.

Modelling dynamic precipitation in pre-aged aluminium alloys under warm forming conditions

This work presents a model for deformation enhanced precipitate growth and coarsening kinetics in pre-aged 7xxx aluminium alloys under warm forming conditions (100 to 200 °C). A multi-class Kampmann–Wagner framework is used to describe the evolution of precipitate size distribution, where the effect of deformation is incorporated through enhanced solute diffusivity resulting from deformation induced excess vacancies. A classical phenomenological model is used to describe the accumulation of excess vacancies. The model is validated with experimental warm deformation data from the literature, and applied to investigate a wide range of deformation conditions to predict the effect of strain, strain rate and temperature on precipitate growth and coarsening kinetics. It is demonstrated that the interaction of solute supersaturation and excess vacancy concentration can lead to complex non-monotonic precipitate growth rate variation for certain regimes of strain rate and temperature.

Analysis of Pore Structure and Thaw Settlement Characteristics of Frozen Silty Sand Based on Computer-Assisted Pulse Nuclear Magnetic Resonance

Computer-assisted pulse nuclear magnetic resonance (NMR) can be used to get important parameters for pore structure characteristics of porous materials. In order to fully understand the effect of frozen soil thaw settlement, the mechanism of artificially frozen soil thaw settlement was examined from a microscopic perspective in conjunction with the frozen soil thaw settlement test. Additionally, to have a better understanding of how pore features change during the thaw settling process, the evolution of the pore size distribution in silty sand was studied. The findings demonstrate the porosity is obviously larger than the initial porosity after freeze-thaw, and the evolution of thaw settlement displacement is related to the change in porosity as thawing progresses, which grows exponentially with porosity. The fraction of medium and large pores (>0.1 μm) in the soil increases significantly during the thawing process. Accordingly, there is a slight increase in the proportion of pores (<0.1 μm) during the thawing progress. The variation in the pore size distribution of silty sand is compatible with that in settlement displacement during the thawing process. Additionally, the thaw settling rate’s development law is consistent with that of the proportion of pores. The number of medium and large pores is critical in determining the rate of thaw settlement. In other words, the development law of thaw settlement rate is consistent with the development law of medium and large pore size distribution.

Cloud Morphology Evolution in Arctic Cold‐Air Outbreak: Two Cases During COMBLE Period

AbstractCloud feedbacks play an important role in Arctic warming. Cloud morphology, for example, cloud size and spatial distributions, is among key factors that directly impact their radiative effects. In this work, we use two cases observed during the Cold‐air Outbreak (CAO) in the Marine Boundary Layer Experiment (COMBLE) to study the evolution of cloud size distributions as an air mass is advected from the Arctic over a comparatively warm ocean and cloud mesoscale organization changes from rolls to cells. Cloud objects are identified from Moderate Resolution Imaging Spectroradiometer (MODIS) reflectance images through an object segmentation procedure and roll breakup is identified by homogeneities in cloud water path (CWP). Roll breakup is found to be accompanied by a local minimum in wind shear and local maxima in cloud size and marine cold air outbreak index. The mean cloud horizontal aspect ratio has weak fetch dependency and is around 2 in roll, transition, and cell regimes. Regardless of distance from the ice edge, smaller clouds (<10 km2) dominate the population number but not cloud cover. Cloud size distributions show bimodality in transition and cell regimes. For clouds with comparable sizes, mean nearest neighbor distances normalized by equivalent cloud radius converge to a single value for all regimes and for all but the smallest clouds, suggesting that clouds of comparable sizes in CAOs are separated by distance proportional to their sizes. The presented statistical results pave the way to evaluating model simulated cloud organizations during CAO events.

Pore size distribution evolution in pellets based bentonite hydration: Comparison between experimental and numerical results

Several nuclear waste disposal concept designs take advantage of bentonite based materials to seal underground galleries and shafts. Safety assessment and long-term predictions of the material behaviour have been the main objective of a number of experimental campaigns and of constitutive models development. All these studies have underlined that the multi-porosity bentonite structure affects undeniably the strongly coupled hydro-mechanical processes taking place during water saturation. Due to this, in recent years, many classic experimental tests on unsaturated soils have been performed in conjunction with multi-scale observation techniques (for instance MIP, i.e. mercury intrusion porosimetry analises). Despite the well-known limitations of such observation methods, they provide interesting quantitative measurements in terms of pore diameters families, which differ by several orders of magnitude, and their distribution with respect to different assemblies' types (namely pellets mixtures and compacted bentonite blocks). On the other hand, very few studies have been focusing on the role of such pore size distributions with respect to the hydro-mechanical response, both from an experimental and a numerical point of view. The aim of this paper is to present the experimental campaign and the numerical modelling strategy adopted to analyse the role of different pore size distributions characterising MX-80 bentonite in different forms (i.e. 32 mm pellets mixture, 7 mm pellets mixture and compacted sample surrounded by gap) with same overall dry density during isochoric hydration tests. Taking advantage of multisensor-equipped cells and post-mortem analyses and of the finite element code LAGAMINE, the hydro-mechanical response of these bentonite assemblies is examined. Experimental and numerical outcomes result in good agreement and provide complementary information regarding the features of each assembly type.

LES of nanoparticle synthesis in the spraysyn burner: A comparison against experiments

The synthesis of iron oxide nanoparticles from iron nitrate in the SpraySyn spray flame reactor was investigated by experiment and simulation. The focus was on the spray and flame structure, the particle growth by nucleation and coagulation, and the unresolved effects and their impact on the dispersed phase. The reacting flow was modeled in large eddy simulations with the premixed flamelet generated manifolds technique, including modifications for aerosol nucleation. Particle dynamics were described with a sectional model and a subgrid scale coagulation kernel. The particle size distributions at different distances from the burner surface were obtained using a particle mass spectrometer. The experiments and simulations are in good agreement for the flame centreline velocity and both size distribution and mean size of the particles (for particles larger 1 nm - the approximate detection limit of the experiment). Furthermore, simulations enabled to interpret the temporal evolution of the particle size distribution.

Size distribution evolution and viscosity effect on spherical submicrometer particle generation process by pulsed laser melting in liquid

Spherical submicrometer particles (SMPs) can be fabricated by pulsed laser melting in liquid (PLML). In this process, raw nanoparticles dispersed in liquid are irradiated by a pulsed laser, heated over the melting point to generate molten droplets, and quenched to form SMPs. The particle size increment is caused by aggregating and merging raw particles in liquid by transient heating. In this study, the viscosity effect on the formation process of SMPs by PLML process is studied by changing aqueous glycerin solution concentration. In highly viscous liquid, smaller SMPs are generated due to the ineffective aggregation process. The temporal evolution of cumulative volume frequency of particles can be simulated, considering the constraints of the non-melting at larger size due to high heat capacity and evaporation for smaller particles by overheating. The SMP size can be controlled by viscosity of the liquid, prior disaggregation time, and liquid temperature.

Effect of Ta microalloying on joint performance by tailoring the microstructure during laser beam welding of Ti-22Al-27Nb

The development of Ti2AlNb based alloys has set a strong competition between conventional Ni-based superalloys and titanium aluminides for aerospace industry due to their compatible/superior mechanical properties. With advent of time, progressive manufacturing technologies are being worked out to transform this novel alloy system into tangible engineering products. Laser beam welding (LBW) of Ti2AlNb based alloys is a provocative task due to evolution of metastable B2 phase in the fusion zone (FZ). In the present study, a comparative analysis on LBW of Ti-22Al-27Nb was carried out by preparing the joints with/without an interlayer of Tantalum (Ta) microfilm. The evolution of microstructure in the weld zone (WZ) was analyzed through Electron probe microanalysis (EPMA), Electron backscattered diffraction (EBSD) analysis, High-angle annular dark-field (HAADF), Bright field (BF) and Selected area electron diffraction (SAED) imaging. The effect of Ta on laser beam welded joint (LBWJ) of Ti-22Al-27Nb was established by correlating the room temperature mechanical properties (tensile properties and hardness) with the evolution of phases, grains and grain size distribution and inter/intra grain misorientations in the weld zone (WZ). The addition of Ta into FZ triggered heterogeneous nucleation, causing epitaxial as well as non-epitaxial mode of solidification in the weld pool. A substantial increase in tensile strength of Ta adulterated LBWJ of Ti-22Al-27Nb was the provenance of grain refinement and greater fraction of high angle grain boundaries (64.89%). The tensile strength and percentage elongation of LBWJ prepared with 0.01 mm thin interlayer of Ta was measured up to 1049 MPa (i.e. 99.15% of that of the base material) and 9.53% respectively. Further dilution of the LBWJ with Ta contributed no significant increase in tensile strength due to nucleation of Intermetallics along the periphery of FZ and caused an early failure.

Coarsening Mechanisms of CaS Inclusions in Ca-Treated Steels

In this work, the coarsening mechanisms of CaS inclusions in liquid steel were investigated by analyzing inclusions in experimental and industrial samples. A detailed particle size distribution evolution was reported. The observed CaS coarsening rate was compared with the theoretical coarsening rate calculated by using the models proposed in the literature. For both experimental and industrial data, it was observed that the coarsening mechanisms varied during different stages of Ca treatment. It was found that in the early stage (after Ca addition) of experiments and during Ca addition under industrial conditions, the coarsening of CaS was governed by diffusion-controlled growth. As the Ca dissolved in steel diminished, the coarsening was governed by collision-dependent mechanisms. For experimental conditions, the growth of CaS was controlled by the Brownian collisions, while the coarsening by turbulent collisions was the dominant mechanism under industrial conditions.

Dust spectral energy distributions in Milky Way-like galaxies in the IllustrisTNG simulations based on the evolution of grain size distribution

ABSTRACT To understand how the evolution of grain size distribution in galaxies affects observed dust properties, we apply a post-processing dust evolution model to galaxy merger trees from the IllustrisTNG cosmological hydrodynamical simulation. Our dust model includes stellar dust production, sputtering in hot gas, dust growth by accretion and coagulation in the dense interstellar medium (ISM), and shattering in the diffuse ISM. We decompose the grain size distribution into different dust species depending on the elemental abundances and the dense ISM fraction given by the simulation. In our previous work, we focused on Milky Way (MW) analogues and reproduced the observed MW extinction curve. In this study, we compute dust spectral energy distributions (SEDs) for the MW analogues. Our simulated SEDs broadly reproduce the observed MW SED within their dispersion and so does the observational data of nearby galaxies, although they tend to underpredict the MW SED at short wavelengths where emission is dominated by polycyclic aromatic hydrocarbons. We find that metallicity and dense gas fraction are the most critical factors for the SED shape, through their influence on coagulation and shattering. The overall success of our models in reproducing the MW SED further justifies the dust evolution processes included in the model and predicts the dispersion in the SEDs caused by the variety in the assembly history. We also show that the most significant increase in the dust SED occurs between redshifts z ∼ 3 and 2 in the progenitors of the simulated MW-like galaxies.

Radiance-based assessment of bulk microphysics models with seven hydrometeor species in forecasting Super-typhoon Lekima (2019) near landfall

Extreme precipitation concerning typhoons brings great losses to coastal cities every year. How to accurately describe the natural cloud and precipitation processes in model remains a major challenge in typhoon forecasts. Observations found rain and hail can both exist under severe typhoon convections. But current operational forecasting models fail to take hail into consideration in super-typhoon prediction. This study assesses the performances of five typical bulk microphysical schemes (BMSs) of the Weather Research and Forecasting (WRF) model in the forecast of Super-typhoon Lekima (2019) near landfall. Unlike other microphysical schemes, all the selected BMSs in this study incorporate seven hydrometeor species including hail, which can represent the hydrometeor distribution within natural super-storm more realistically as supported by field observational facts. Through statistical-physical evaluation processes and using radar-satellite joint observations, the goal is to identify the best scheme to accurately forecast Super-typhoon Lekima and to find the future avenue to possible microphysical scheme improvement. It is found that the WRF double-moment 7-class (WDM7) scheme exhibits the smallest root mean square error (RMSE) of approximately 1.5 for both composite reflectivity and brightness temperature signatures, and predicts the closest macro-physical hydrometeors structure, amplitude and location to observations. Moreover, the azimuthal mean brightness temperature distributions suggest large forecasting errors over typhoon inner rainband, with WDM7 scheme performing best. The vertical reflectivity profiles further suggest that WDM7 scheme could well characterize the updraft, water content, and cold-cloud processes, but needs further improvement in the representation of warm-cloud processes. The performances of BMSs are found to be closely related to the moments used to describe the evolution of the drop size distribution. Among all the schemes, the double-moment schemes generally perform better in simulating warm-cloud processes, while the single-moment schemes show better performance in simulating cold-cloud processes. As a partially double-moment and partially single-moment scheme, WDM7 scheme exhibits unique advantages over the others. The optimum choice of moments is an important step toward the future improvement of BMS.

Residual Stresses Measurements in Laser Powder Bed Fusion Using Barkhausen Noise Analysis.

In recent years, the advancement of technology brought the laser powder bed fusion process to its industrialisation step. Despite all the advancements in process repeatability and general quality control, many challenges remain unsolved due to the intrinsic difficulties of the process, notably the residual stresses issue. This work aimed to assess the usability of Barkhausen noise analysis (BNA) for the residual stress in situ monitoring of laser powder bed fusion on Maraging steel 300 (18Ni-300/1.2709). After measuring the evolution of grain size distribution over process parameter changes, two series of experiments were designed. First, a setup with an external force allows to validate the working principle of BNA on the chosen material processed using LPBF. The second experiment uses on-plates samples with different residual stress states. The results show a good stability in microstructure, a prerequisite for BNA. In addition, the external load setup acknowledges that signal variation correlates with the induced stress state. Finally, the on-plate measurement shows a similar signal variation to what has been observed in the literature for residual stress variation. It is shown that BNA is a suitable method for qualitative residual stresses variation monitoring developed during the LPBF process and underlines that BNA is a promising candidate as an in situ measurement method.

Evolution of the particle size distribution of tricalcium silicate during hydration by synchrotron X-ray nano-tomography

The particle size distribution of tricalcium silicate (C3S) is essential for the modelling of early C3S hydration kinetics. In this study, this parameter is analysed during the main hydration period until the first 20 h by synchrotron near-field ptychographic (NF-PXCT) and holographic (HXCT) computed nano-tomography. Additionally, X-ray diffraction, 29Si NMR, thermal analysis, scanning electron microscopy, and inductively coupled plasma-optical emission spectroscopy were used to investigate the system evolution. The time-dependent pore solution composition is also provided to gain further information.HXCT and NF-PXCT show comparable values regarding the evolution of the C3S particle size distribution during hydration, indicating that C3S particles smaller than 1.3 μm are completely dissolved after 20 h of hydration. The results can be reasonably reproduced by numerical models if for all particle sizes a constant reacted rim thickness for each degree of hydration is assumed. Data on the aqueous phase composition are also provided.

Similarities in Evolution of Aggregate Size Distributions during Successive Wetting and Drying Cycles of Heavy Textured Soils of Variable Clay Mineralogy

A phenomenon causing instability of soil structure and associated hydraulic properties in recently tilled soils is aggregate fragmentation induced by wetting and drying cycles. We analyzed data from three experiments in Puerto Rico, the UK and China measuring fragmentation and resulting evolution of aggregate size distributions during successive wetting and drying cycles in heavy textured soils. Aggregate distributions were represented as the cumulative fraction F of aggregates passing through successively larger sieve sizes X. To a good approximation, all distributions exhibited similarity in that the aggregate diameter X(F) corresponding to F in a given test distribution was always a characteristic multiple α¯ of X(F) in a fixed reference distribution, where α¯ for a distribution was calculated as its mean weight aggregate diameter (MWD) divided by the MWD of the reference distribution. In most cases, α¯ for a given soil varied inversely with the square of the number of wetting and drying cycles. For different soils of similar initial aggregate sizes, α¯ for a given wet–dry cycle decreased with increasing activity coefficient, reflecting the enhancing effect of soil shrink–swell potential on fragmentation. Results highlight usefulness of the van Bavel mean weight diameter as a natural scaling parameter for characterizing aggregate distributions.

Evolution process and stabilization mechanism of different gas nanobubbles based on improved statistical analysis

AbstractNanobubbles (NBs) have attracted increasing attention due to their unique physicochemical characteristics and enormous potential industrial applications in the biology, environment, medicine, and many other fields. A complete understanding of the underlying stability mechanism of NBs is an essential requirement for their research, development, and industrial applications. In this study, a facile and reliable approach to generating different gas NBs using a porous ceramic membrane is reported. In addition, an improved method of statistical analysis to predict NB size distribution is proposed. The results indicated that the gas NBs presented a log‐normal distribution due to an underlying Ostwald ripening process. The concentration of NBs in solution was controlled by the gas type owing to different magnitude of molecular polarizability of dissolved gases. The mean size of the NB was inversely proportional to the surface charge density. Moreover, the NB stability lies in a special state at the bubble interface, not only because the presence of surface charges hinders collisions between bubbles, but also because the degree of gas supersaturation of molecules around bubbles resulting in gas exchange has a certain stabilizing effect, and also controls the evolution of particle size distribution (PSD) for different bulk NBs.

Observed and Bin Model Simulated Evolution of Drop Size Distributions in High‐Based Cumulus Congestus Over the United Arab Emirates

AbstractThis study examines microphysical processes in developing high‐based cumulus congestus over the United Arab Emirates using aircraft observations and a large‐eddy‐simulation model with bin microphysics. A notable feature of this case is the lack of mm‐sized drops despite having a liquid cloud layer km deep, contrasting with copious large drops observed in maritime tropical cumulus congestus having a similar vertical extent. Modeled drop size distributions are similar to observations at various temperatures between 9.5 and −12°C, including the lack of mm‐sized drops. Cloud dilution leads to low‐to‐moderate liquid water contents (∼0.5–1.5 g m−3) in most of the cloud core, several times smaller than adiabatic values. Dilution is enhanced in the inflowing branch of the toroidal circulations associated with individual cloud thermals, which are favored regions for secondary droplet activation (activation above cloud base). Secondary activation in general contributes substantially to the droplet population. Turning it off leads to a sharp decrease in droplet concentration and increase in mean size aloft, but does little to increase rain drop production. Warm rain generation (or lack thereof) in this case is therefore determined more by the sub‐cloud aerosol and the cloud base droplet size distribution (DSD) than DSD evolution aloft from secondary droplet activation. Decreasing the aerosol concentration by a factor of 10 greatly increases production of large drops via collision‐coalescence. Thus, despite its high base (low temperatures) and substantial dilution, the simulated cloud is thermodynamically and dynamically capable of rapidly producing copious mm‐sized drops from collision‐coalescence under pristine aerosol conditions.

A bimodal population balance method for the dynamic process of engineered nanoparticles

The evolution of size distribution of engineered nanoparticles (ENPs) from the gas phase to the product in chemical reactors is a complicated heat and mass transfer process, whose mathematical description is commonly characterized by the population balance equation (PBE) in terms of particle number concentration. This study presents a new population balance model (PBM) for resolving the evolution of PBE for ENPs using a bimodal inverse Gaussian distributed method of moments (BIGDMOM). In this method, engineered nanoparticles’ size distribution is constructed by superposing two inverse Gaussian subdistribution. A close model for arbitrary moments is then obtained for achieving the final solution of the population balance equation for ENPs. The precision of BIGDMOM, which is verified in the test cases of two representative ENPs dynamics, is acceptable compared with widely used methods, such as log-normal MOM (log MOM), third-order Taylor-series expansion MOM, and unimodal IGDMOM, for key statistical quantities determining ENP size distributions, including kth moments (k = 0, 1/3, 2/3, and 2), shape factor, mean, and variance, sometimes is even better. Therefore, this study provides a new bimodal particle size distribution for the moment method, which can be used as an option to explore the specific bimodal practical problems of ENPs in the future.

Modelling the hydrodynamics and kinetics of methane decomposition in catalytic liquid metal bubble reactors for hydrogen production

Bubble reactors using molten metal alloys (e.g, nickel-bismuth and copper-bismuth) with strong catalytic activity for methane decomposition are an emerging technology to lower the carbon intensity of hydrogen production. Methane decomposition occurs non-catalytically inside the bubbles and catalytically at the gas-liquid interface. The reactor performance is therefore affected by the hydrodynamics of bubble flow in molten metal, which determines the evolution of the bubble size distribution and of the gas holdup along the reactor height. A reactor model is first developed to rigorously account for the coupling of hydrodynamics with catalytic and non-catalytic reaction kinetics. The model is then validated with previously reported experimental data on methane decomposition at several temperatures in bubble columns containing a molten nickel-bismuth alloy. Next, the model is applied to optimize the design of multitubular catalytic bubble reactors at industrial scales. This involves minimizing the total liquid metal volume for various tube diameters, melt temperatures, and percent methane conversions at a specified hydrogen production rate. For example, an optimized reactor consisting of 891 tubes, each measuring 0.10 m in diameter and 2.11 m in height, filled with molten Ni0·27Bi0.73 at 1050 °C and fed with pure methane at 17.8 bar, may produce 10,000 Nm3.h−1 of hydrogen with a methane conversion of 80% and a pressure drop of 1.6 bar. The tubes could be heated in a fired heater by burning either a fraction of the produced hydrogen, which would prevent CO2 generation, or other less expensive fuels.

In vitro gastric digestion and emptying of cooked white and brown rice using a dynamic human stomach system

In this study, a dynamic in vitro human stomach system was employed to elucidate the influence of structural differences between white and brown rice on gastric emptying and starch digestion. The evolution of gastric digesta particle size distribution, pH, viscosity and starch hydrolysis was investigated during digestion. Due to the protective effect of the outer bran layer against structural breakdown, brown rice showed higher pH buffering capacity, larger digesta particle size and greater rheology, resulting in a delayed gastric emptying and consequently, lower starch hydrolysis in an overall starch digestibility in the stomach than the white rice. The current study has provided quantitative evidence regarding the importance of macrostructure (i.e. the bran layer) in rice gastric digestion that may further impact intestinal absorption. Meanwhile, the particle size was significantly smaller in the digesta emptied out of the stomach in both white and brown rice throughout the digestion compared to that retained in the stomach. This demonstrates an effective size reduction and sieving efficiency exhibited by the in vitro system. It is practically meaningful to use the in vitro system to track the dynamic changes in structural and physicochemical properties of food materials during digestion in the stomach.