Particle Number Density Research Articles

Property of water-nanoparticle flow and heat transfer in the double-tube heat exchanger with nanofluid

The three-dimensional numerical simulation is conducted to study the impact of Al2O3/water nanofluid on the flow property and heat transfer of a counter flow double-tube heat exchanger where a laminar flow of cold water is in the outer tube, and in the inner tube there is a turbulent flow of hot nanofluid with particle volume concentrations ranging from 0.05% to 3%. The effects of temperature, flow rate, and particle volume concentration on the property of nanofluid flow and heat transfer are explored. The results show that the friction factor decreases with the increase of temperature and flow rate, and the pressure drop increases with increasing particle volume concentration. The temperature of the nanofluid at the outlet first decreases rapidly with time and then increases gradually to a stable value. Along the flow direction, the temperature of nanofluid decreases slowly at x/D < 10, and the axial temperature gradient increases at the full development stage. At a constant Reynolds number, the lower the temperature or the larger the particle volume concentration, the stronger the heat transfer. The local heat transfer coefficient on the wall of the inner tube decreases rapidly after reaching the peak x/D = 2.3, and then increases slowly until the outlet. The particle number density decreases sharply at x/D < 5, and then slowly decreases, while the change of the geometric mean diameter of particles is just the opposite. Increasing the flow rate or the temperature will strengthen particle coagulation, resulting in the decrease of particle number density and the increase of geometric mean diameter of particles.

A framework to characterize WUI firebrand shower exposure using an integrated approach combining 3D particle tracking and machine learning

Firebrand showers are known for their devastating effects throughout Wildland-Urban Interface (WUI) communities threatened by wildfires. In this work, we propose a framework to better characterize firebrand flows and facilitate exposure comparisons across experimental cases. This framework leverages the National Institute of Standards and Technology (NIST) Emberometer, a measurement device that allows time-resolved motion tracking of burning particles in full 3D space. An improved version of the Emberometer, geared towards field use with enhanced firebrand detection capability and data processing pipelines, is presented. The device was used to investigate, in outdoor settings, a firebrand shower artificially generated to produce mixed amounts of smoldering and flaming particles. The ability to perform meaningful quantitative exposure comparisons, via metrics such as Cumulative Particle Count (CPC) and Particle Number Flux (PNF), is demonstrated. A sub-set of 3D-tracked firebrand images was used to train several Convolutional Neural Networks (CNN) to recognize firebrand combustion state. The best performing model was selected to process the entire tracking dataset (over 70,000 firebrand images), and time-resolved volumetric number densities of both smoldering and flaming particles were derived, a first for complex airborne firebrand flows.

Effects of oxygen addition to the fuel stream on the soot formation in an ethylene coflow partially premixed flame based on the orthogonal decoupling method

In this work, an orthogonal decoupling method based on the orthogonal design and decoupling method was used to simulate the effects of adding oxygen (O2) to the fuel stream on the soot formation characteristics in an ethylene (C2H4) coflow partially premixed flame. The dilution effect, thermal effect and chemical effect of the added O2, as well as the interaction between these effects were decoupled and analyzed. Results show that the peak soot volume fraction (SVF) in the flame decreases first and then increases as the O2 mole fraction gradually increases to 30%, and is lowest at an addition of 20%. The orthogonal decoupling calculations were performed for two O2 concentration ranges of 5%–10% and 25%–30%, and the differences on soot formation at these two ranges were found to be dominated by the chemical effects of O2 through the extremum difference analysis of the calculated peak SVF, number density of primary particle and particle aggregation degree. The chemical effect of O2 inhibits the formation of soot at an O2 addition of 5%–10%, while promotes the formation of soot at an O2 addition of 25%–30%, by affecting the inception, hydrogen-abstraction-carbon-addition (HACA) reaction, and polycyclic aromatic hydrocarbon (PAH) condensation rates of soot formation. When the O2 concentration is 25%–30%, the chemical effect of O2 promotes the soot surface growth rate and therefore increases the soot particle size, which in turn retards the complete oxidation process, leading to an increase in SVF.

Fast Radio Bursts Generated by Coherent Curvature Radiation from Compressed Bunches for FRB 20190520B

The radiation mechanism of fast radio bursts (FRBs) has been extensively studied, but still remains elusive. Coherent radiation has been identified as a crucial component in the FRB mechanism, with charged bunches also playing a significant role under specific circumstances. In the present research, we propose a phenomenological model that draws upon the coherent curvature radiation framework and a magnetized neutron star, taking into account the kinetic energy losses of outflow particles due to inverse Compton scattering (ICS) induced by soft photons within the magnetosphere. By integrating the ICS deceleration mechanism for particles, we hypothesize a potential compression effect on the particle number density within a magnetic tube/family, which could facilitate achieving the necessary size for coherent radiation in the radial direction. This mechanism might potentially enable the dynamic formation of bunches capable of emitting coherent curvature radiation along the curved magnetic field. Moreover, we examine the formation of bunches from an energy perspective. Our discussion suggests that within the given parameter space, the formation of bunches is feasible. Finally, we apply this model to FRB 20190520B, one of the most active repeating FRBs discovered and monitored by FAST. Several observed phenomena are explained, including the basic characteristics, frequency downward drifting, and bright spots within certain dynamic spectral ranges.

Sn–Sc microalloying-induced property improvement and micromechanisms of an Al–Mg–Si alloy

Microalloying is of great importance for the property modulation of lightweight high-strength aluminum alloys. Little is known, however, about the properties and micromechanisms of Al–Mg–Si alloys microalloyed with Sn and Sc. In this work, the property changes of Al–0.5Mg–0.4Si (wt%) alloys induced by 0.1Sn and 0.1Sn–0.1Sc (wt%) additions and underlying alloying mechanisms are revealed by atomic-scale transmission electron microscopy and first-principles calculations. The results show that the Sn–Sc coaddition results in a decreased diameter and an increased number density of the Sc-containing constituent particles of Mg2Si and Mg2(Si,Sn), as compared to the sole Sn addition. The featured Si-site columns in β'', B′ and β′ structures can be occupied by Sn and Sc. Substantial peak-aging β'' needles with confined cross-sectional coarsening are observed for the Sn–Sc containing alloy compared to the Sn containing alloy. The modified constituent particles and precipitates improve the plasticity and strength of peak-aging Al–Mg–Si–Sn–Sc alloy. The elevated peak-aging corrosion resistance and over-aging thermal stability of Al–Mg–Si–Sn–Sc alloy are associated with the sparse Sc-containing Mg2(Si,Sn) grain boundary precipitates and low strain filed of Al matrix around the β′ containing Sn/Sc, respectively. The obtained results are hoped to guide the design of high-performance Al alloys.

Dissolution-induced oxide synthesis using SiO2 microparticles for oxide dispersion strengthening of Fe-based alloys

This study reports on a single-track laser surface alloying process that utilizes SiO2 powder to disperse both SiO2 particles and oxide inclusions in 316L stainless steel for oxide dispersion strengthening (ODS) purposes. In this process, the SiO2 powders partially dissolve in the melt pool, and the released silicon and oxygen atoms nucleate to form oxide inclusions in-situ within the metal matrix. This dissolution-induced oxide synthesis route demonstrated a high potential for ODS, achieving a high particle number density (6.6 × 104 mm−2) and area fraction (3.3%) comparable to that of bulk 316L samples produced via directed energy deposition. The hardness of the SiO2/316L composites reached a maximum of 232.4 HV compared to that of the 316L substrate (average 170.8 HV). The improvement in hardness was theoretically explained and quantified, significantly originating from the enhanced dislocation density strengthening mechanism resulting from the large difference in the coefficient of thermal expansion between SiO2 and 316L.

Investigation of the Rayleigh–Taylor instability in charged fluids

The present study shows that the Rayleigh–Taylor (RT) instability and its growth rate are strongly dependent on the charge-mass ratio of charged particles in a charged fluid. A higher charge-mass ratio of the charged fluid appears to result in a stronger effect of the magnetic field to suppress the RT instability. We study the RT instabilities for both dusty plasma (small charge-mass ratio of charged particles) and ion-electron plasma (large charge-mass ratio of charged particles). It is found that the impact of the external magnetic field to suppress the RT instability for ion-electron plasma is much greater than that for dusty plasma. It is also shown that, for a dusty plasma, in addition to region parameters such as the external magnetic field, region length, its gradient, as well as dust particle parameters such as number density, mass, and charge of dust particles, the growth rate of the RT instability in a dusty plasma also depends on parameters of both electrons and ions such as the number densities and temperatures of both electrons and ions.

Enhancing efficiency in particle aggregation simulations: Coarse-grained particle modeling in the DEM-PBM coupled framework

The computational cost of the discrete element method (DEM)-population balance model (PBM) coupled framework is predominantly attributed to DEM simulations. To overcome this challenge, coarse-grained (CG) particles have been introduced in the DEM-PBM coupled framework. In this study, we proposed a new CG-enabled DEM-PBM coupled framework that builds upon the previous work of Das et al. (Proc. R. Soc. Lond. Ser. A Math. Phys. Eng. Sci. 478 (2261) (2022) 20220076). By incorporating the CG technique, the particle number density is reduced, resulting in fewer collisions compared to the resolved system. To address this issue, a scaling law has been developed to derive the collision frequency of the resolved system from the CG system. The verification of the new scaling law has been demonstrated through various simulation studies. Furthermore, the entire DEM-PBM coupled framework has been modified using the proposed methodology. The efficiency of the CG–DEM–PBM coupled simulation method has been successfully demonstrated through simulations of rotating drum and continuous mixing technology (CMT). Compared to the resolved simulation approach, the newly proposed CG-enabled DEM-PBM coupled framework maintains accuracy in terms of particle size distribution and other essential findings while significantly reducing simulation time.

New semi-analytical approach and its convergence analysis for a classical hyperbolic fragmentation model: A homotopy perturbation method

In the past few decades, the homotopy perturbation method (HPM) has been used intensively for finding analytical and semi-analytical solutions for linear and nonlinear differential equations. This method is well-known for its flexibility and efficiency to solve complicated physical problems. Moreover, HPM offers physical insight into the underlying dynamics of the system, as well as on the evolution of solutions. In this work, HPM is employed to obtain semi-analytic solutions for the hyperbolic particle-fragmentation equation. A recursive scheme is derived for finding the approximate solution. Mathematical formulation of the scheme is further studied by conducting a detailed convergence analysis of the method. Different physics-embedded test problems are solved using this recursive scheme and their series solutions are obtained. The proposed method is validated by comparing the approximated solutions with the exact results. For two test problems, new series solutions are presented in closed form. New analytical solutions are obtained for the particle number density c(x,t), with breakage kernels ℱ(x,y)=1,x+y, and initial condition c(0,x)=exp(−x)x. Moreover, the analytical solutions for ℱ(x,y)=1x+y corresponding to initial conditions c(0,x)=exp(−x) and exp(−x)x are derived for the first time in literature. Due to the non-availability of the analytical solutions of the particle density functions, the results are verified against the finite volume scheme (Saha and Bück, 2021). It is observed that the proposed method predicts the particle density as well as significant integral moments with high accuracy by considering only a fewer number of terms in the series solution.

Influence of Thermionic Emission on He Ionization and Plasma Enhancement in Thermionic Energy Conversion

In this paper, the influence of thermionic emission on He ionization and plasma enhancement in thermionic energy conversion (TEC) are studied by experiment and numerical simulation. A 1D unsteady plasma TEC model, which includes a He ionization model, plasma conservation equations, and a thermionic emission formula for the wall, is developed. A He plasma thermionic energy conversion device composed of a barium–tungsten cathode and a tungsten anode is established. The volt–ampere curves of the He plasma TEC device are measured at 1050 K, 1150 K, 1250 K, 1300 K, and 1350 K temperatures. Both important cathode parameters, work function and emission area, are estimated. Based on the modelling simulation and the experiment, the He ionization mechanism in plasma TEC is discovered. The effects of cathode temperature on several distributions of plasma reaction rates, particle number density, and potential in He plasma TEC are described. Some important parameters, including electron mobility, resistivity, and plasma equilibrium are analyzed. The relationship of thermionic emission on plasma enhancement to the output power of plasma TEC is presented. The output powers of plasma TEC and vacuum TEC are compared at various cathode temperatures. A dimensionless analyzing method concerning thermionic emission intensity and plasma enhancement power is proposed. A brief dimensionless relationship is deduced regarding thermionic emission intensity and the plasma enhancement contribution of TEC. The principles and methods for quantitative calculations concerning the output power of plasma TEC under the action of thermionic emission are established. It is possible to do quantitative research on the effects of thermionic emission on plasma-enhanced TEC.

Induced Wigner crystallization in a coupled electron-hole quantum wire system at finite-temperature

We explore the possibility of induced Wigner crystallization in a coupled electron-hole (e-h) quantum wire system at finite-temperature T by calculating the intra- and inter-wire static structure factors in the dynamic mean-field approximation of Singwi et al (the qSTLS theory). We find that owing to the dynamics of severely correlated particles, the e-h system may favour an induced phase transition from quantum liquid to the Wigner crystal state at a non-zero T and sufficiently low particle (electron/hole) number density in the close proximity of two wires. On the other hand, the static STLS approximation does not predict such phase transition due to complete neglect of the dynamics of particle correlations.

Experimental study of turbulent thermal diffusion of particles in an inhomogeneous forced convective turbulence

We investigate experimentally the phenomenon of turbulent thermal diffusion of micrometer-size solid particles in an inhomogeneous convective turbulence forced by one vertically oriented oscillating grid in an air flow. This effect causes the formation of large-scale inhomogeneities in particle spatial distributions in a temperature-stratified turbulence. We perform detailed comparisons of the experimental results with those obtained in our previous experiments with an inhomogeneous and anisotropic stably stratified turbulence produced by a one oscillating grid in the air flow. Since the buoyancy increases the turbulent kinetic energy for convective turbulence and decreases it for stably stratified turbulence, the measured turbulent velocities for convective turbulence are larger than those for stably stratified turbulence. This tendency is also seen in the measured vertical integral turbulent length scales. Measurements of temperature and particle number density spatial distributions show that particles are accumulated in the vicinity of the minimum of the mean temperature due to the phenomenon of turbulent thermal diffusion. This effect is observed in both convective and stably stratified turbulence, where we find the effective turbulent thermal diffusion coefficient for micrometer-size particles. The obtained experimental results are in agreement with theoretical predictions.

A free-surface particle regularization scheme based on numerical integration for particle methods

Particle shifting model plays a significant role in regularizing particle distribution in high-order accuracy Lagrangian particles methods. However, due to the incomplete neighbouring support of surface particles, the treatment of particle shifting models applied to free-surface particles still deserves attention from researchers. A new free-surface particle regularization scheme based on numerical integration (NIPS) for particle methods is proposed in this study. Specifically, high-resolution surrounding meshes are seeded outside the free surfaces to supplement the incomplete neighbouring support. Then, the contribution of the void region outside the free surface to the particle shifting vector is numerically integrated based on the surrounding meshes. The appropriate resolution and the screen scheme for constructing the surrounding meshes are optimized in this study. This scheme is easy to implement because the particle number density is only employed to screen the surrounding meshes. A typical high-order accuracy particle method, the LSMPS method is taken to evaluate the proposed scheme in this study. Numerical examples demonstrated that the proposed regularization method can keep uniform distribution of surface particles, thus the instability due to heterogeneous surface particles distribution can be effectively avoided.

Effect of the surface water content on dry saltation cloud dynamics: A wind tunnel simulation with particle tracking velocimetry

AbstractThe mass transport rate of wind‐borne particles, and indeed the fluid stress required for their entrainment, is strongly governed by inter‐particle cohesion arising from water retained through adsorption and capillary force. This paper reports on a series of wind tunnel experiments in which high‐speed photography was used to record the motion of dry sand particles as they impinged on test beds of systematically varied target gravimetric pore water content (0% ≤ W ≤ 10%). The wind friction velocity was preset to 0.33 m s−1, sufficient to maintain a saltation cloud above an upwind strip of dry sand, which then was blown over the wetted surface. Discrete particle trajectories were identified in the camera images using expected particle area searching–particle tracking velocimetry (EPAS‐PTV). Adding progressively more water produced an exponential decrease in the normalized particle number density over the test surface. The largest response was achieved by wetting the bed surface to just 2%. To reduce the number of particles by a further 40%, it was necessary to add eight times more water, signifying a diminishing return regarding water use. Relative to particles either rebounding or splashed from a dry bed, the total particle velocity increased incrementally by a factor between 1.5 and 2 with increasing water content. Increasing amounts of pore water were associated with progressively higher saltation trajectories, reaching a plateau beyond W ~8%. The spatio‐temporal adjustment in the sand cloud was observed to be extremely rapid. There is no consensus in the literature on how to measure the water content that effectively governs aeolian transport. In this study, all approaches to sampling W produced strong correlation (R2 ≥ 0.85). Sampling the topmost grains, however, provided the most accurate prediction of the normalized number density over the full range of water content.

Silica Nanoparticle Formation from Supercritical Geothermal Sources

Silica precipitation from high-enthalpy, depressurized supercritical fluids is investigated to determine the best method for accessing the scaling potential as a function of time, position and fluid composition. The most relevant knowledge application is for geothermal sources where the wells are drilled closed to magma and the temperature gradients in the rock are very high. The power potential per well for such a system is large compared to conventional geothermal power production, but several knowledge gaps, among them mineral precipitation from produced fluids, limit commercial use. For the high-enthalpy supercritical well fluid used as a base case in this review, conventional methods for reducing the silica content before it enters a turbine limit the power output. Knowledge of the particle-number density, size and time scales of growth in different depressurization scenarios, along with the silica solubility, kinetics and morphology, is essential to handle deposits and avoid scaling in inconvenient parts of the power plant. Experimental data on the precipitation of silica from highly supersaturated superheated steam are scarce, and it is known that the kinetics of precipitation in steam differ from those of liquid water. We argue that to quantify the number of solids in the depressurized supercritical fluid and superheated steam, dividing the process into three separate but dependable mathematical steps is a reliable approach: (1) the nucleation of nanocolloids, (2) growth by agglomeration, and (3) deposition onto a surface.

Iron Oxide Nanocubes as a New Certified Reference Material for Nanoparticle Size Measurements.

The rational design and increasing industrial use of nanomaterials require a reliable characterization of their physicochemical key properties like size, size distribution, shape, and surface chemistry. This calls for nanoscale reference materials (nanoRMs) for the validation and standardization of commonly used characterization methods closely matching real-world nonspherical nano-objects. This encouraged us to develop a nonspherical nanoRM of very small size consisting of 8 nm iron oxide nanocubes (BAM-N012) to complement spherical gold, silica, and polymer nanoRMs. In the following, the development and production of this nanoRM are highlighted including the characterization by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) as complementary methods for size and shape parameters, homogeneity and stability studies, and calculation of a complete uncertainty budget of the size features. The determination of the nanocubes' edge length by TEM and SAXS allows a method comparison. In addition, SAXS measurements can also provide the mean particle number density and the mass concentration. The certified size parameters, area equivalent circular diameter and square edge length, determined by TEM with a relative expanded uncertainty below 9%, are metrologically traceable to a natural constant for length, the very precisely known (111) lattice spacing of silicon. Cubic BAM-N012 qualifies as a certified nanoRM for estimating the precision and trueness, validation, and quality assurance of particle size and shape measurements with electron microscopy and SAXS as well as other sizing methods suitable for nanomaterials. The production of this new iron oxide nanocube RM presents an important achievement for the nanomaterial community, nanomaterial manufacturers, and regulators.

Thermophysical Properties of Air-PA66-Copper Plasmas for Low-Voltage Direct Current Switches

This paper presents the thermophysical properties of an air-PA66-copper mixture in thermal plasma. Equations based on mass action law, conservation of neutrality and perfect gas law are used to calculate particle number densities. Thermodynamic properties and transport coefficients were obtained from equilibrium compositions and computed using the Chapman-Enskog method. Radiative properties are described in terms of the total absorption coefficient and the net emission coefficient

The Scattering and Absorption Coefficients of Atmospheric Soot in the Hygroscopicity of Urban Aerosols

Aerosols are microscopic solid or liquid particles suspended in the atmosphere that have an impact on the Earth's radiative balance. This paper modeled and investigates the effect of scattering and absorption coefficients along with their respective hygroscopicity of atmospheric soot using extracted data from Optical Properties of Aerosols and Clouds (OPAC) incorporated with Fortran at spectral range of 0.25 to 1.00 m for eight different relative humidities (RHs) (0, 50, 70, 80, 90, 95, 98 and 99%). The fine – mode and coarse – mode aerosol size distribution were also investigated. The particle number densities of soot were varied as 110,000 120,000 and 130,000 cm-3 while the water soluble and insoluble components were kept constant. The scattering coefficient decreases with RHs and also with wavelength in the form of power law at all RHs. The absorption coefficient increases with addition of soot, reflecting warming effect. In this study, it was observed that there is a pronounced hygroscopicity growth as from 95-99% RHs. The Ångström exponent decreases with increase in RHs for the case of scattering coefficient but varies for absorption coefficient; the curvature reveals the presence of both fine and coarse mode particles. The results of the turbidity coefficient (????) based on the scattering coefficient indicated that the atmosphere is relatively clear and hazy while the absorption coefficient indicated that the atmosphere is relatively clear at 0 – 99% relative humidity. The results in this study revealed that the coefficient of determination, ???? 2 &gt; 96% for all the models (1 – 3).

Phase-Field Modeling of Spinodal Decomposition in Fe–Cr–Co Alloy under Continuous Temperature-changing Conditions

Fe-Cr-Co alloys are becoming important as a half-hard magnet for their novel applications, including non-contact electromagnetic brakes, because of the controllability of its magnetic hardness depending on the modulated structure formed by spinodal decomposition. However, the experimental optimization of the complicated heat-treatment process to control the microstructure significantly increases the development cost, and microstructure prediction by computational simulation is desired. In this study, we first developed the method of phase-field simulation for spinodal decomposition in Fe-Cr-Co alloy during various heat treatments, including isothermal heat treatment, multistep continuous fast and slow cooling, which allows us to conduct a simulation of spinodal decomposition under conditions close to the condition of practical heat treatment. The simulation results revealed that the morphology of the modulated structure is predominantly determined by the cooling rate and does not change significantly during the subsequent isothermal annealing process, while the difference between the concentrations of the FeCo-rich magnetic phase and the Cr-rich non-magnetic phase increases. Continuous cooling at rates higher than 140 K/h demonstrates the maximum number densities of the ferromagnetic particles of α1-phase seemingly almost reaching saturation, which is expected to give rise to exhibiting the largest coercive force of the Fe-Cr-Co magnet. Moreover, this method can be extended to other materials for designing a modulated structure to show a desired property.

Comparative study of NH3 and H2 impacts on combustion and emission characteristics of n-Hexadecane under different flame conditions

The addition of renewable fuel to hydrocarbon fuel mitigated the carbon monoxide, carbon dioxide and soot particle emissions of internal combustion engines. A comparative study of the ammonia and hydrogen effect on combustion and emission characteristics of n-hexadecane flames was executed at various flame conditions. The results showed that alternative fuels had a stronger impact on peak temperature at diffusion flame conditions rather than at premixed flame conditions. The premixed flame released carbon monoxide emission lower than the diffusion flames with/without additional fuels. The carbon monoxide emissions decreased highly with ammonia enrichment instead of hydrogen. At premixed and coflow diffusion flame conditions, the ammonia highly reduced carbon dioxide emission compared to hydrogen. Hydrogen addition reduced the nitrogen oxide emission, whereas it was increased by ammonia. The soot particle number density was reduced highly by hydrogen addition instead of ammonia at the premixed flow flame and diffusion coflow flame conditions. The impact of hydrogen on the reduction of soot mass concentration emissions was greater than that of ammonia at all combustion conditions. It is suggested that H2 ≥ 70% should be mixed in n-hexadecane fuel because a higher burning velocity can be achieved with a higher emission reduction. A reduction in the emission of carbon-related species can be realized with a small reduction in burning velocity at NH3 < 70%.