Small Fraction Of Particles Research Articles

Study on the Membrane Fouling Process and Mechanism of Constant Pressure Filtration in Stirred Membrane Reactors

Stirred membrane reactors allow for catalyst recycling and product separation. However, membrane fouling becomes a major problem limiting such reactors. In this work, the dynamic process and mechanism of constant pressure filtration membrane fouling were investigated through experiments combined with computational fluid dynamics (CFD) simulation. The results show that according to the Hermia model, the filtration model at the high shear position is the cake filtration model, and the filtration model at the low shear position is the combined filtration model due to the different particle accumulation speeds. Second, the stronger the shear rate or the lower the transmembrane pressure, the easier it is for the filtration system to stabilize. However, the smaller the porosity ε, the larger the fraction of small particles in the filter cake. Finally, this work explains the mechanism of membrane fouling from the changes in particle radial velocity and acceleration at the micro level.

Effect of Particle Size of a Powder upon the Properties and Microstructure of Boron-modified Fe-Ni-Mo-Cu Sinters

The article discusses the effect of different particle fractions of prealloyed iron powder on the microstructure, density and hardness of sintered material. Each particle fraction (apart from 160–200 µm, which is a trace fraction) was modified with boron, its contents being, respectively, 0.2 wt.%, 0.4 wt.% and 0.6 wt.%. Next, the powder mixtures were pressed under a pressure of 600 MPa, and the final compacts were subject to sintering at 1200°C for 60 min in a hydrogen atmosphere. It was observed that the higher values of density and hardness were found in samples made from finer fractions of powder. A higher homogeneity of the microstructure and the highest degree of compactness was obtained in sinters from powder of 40–56 µm particle size, with 0.4 wt.% boron. Due to the use of small particle fractions of prealloyed powder, a higher degree of compactness in sinters was obtained with lower boron content. Also indicated was which particle fraction of Fe-Ni-Mo-Cu powder should be applied to obtain density in sinters with boron addition equal to almost 100% of the relative density of the analyzed alloy. The presented studies have both scientific and technological aspects.

Sintered Fe-Co-Si alloy with excellent magnetic and mechanical properties by coherent precipitation of submicrometer-sized carbide particles

A novel sintered Fe-Co-Si alloy with coherent precipitation of submicrometer-sized carbide particles of Ta3Co3C containing iron and silicon is fabricated by a unique synthesis route through evaporation of an Fe-Co-Si matrix and diffusion of tantalum and carbon by sintering in high vacuum at a high temperature. The carbide particles precipitate homogeneously on the surface, in the grain boundaries, and inside the grains of the matrix. In particular, many particles precipitate homogeneously along the grain boundaries, which can contribute to improving mechanical strength by preventing intergranular fracture in spite of very small volume fraction (0.8 vol%) of the precipitated particles. The strength improvement can be explained by the particle shearing mechanism by the coherent precipitation of carbide particles. The orientation relationships between the carbide particles and Fe-Co-Si matrix are (4̅04)particle//(2̅02)matrix, (04̅0)particle//(02̅0)matrix, and (4̅00)particle//(2̅00)matrix with a very small lattice mismatch (<2%). As a result of the coherent precipitation, the magnetic properties such as low magnetic loss and high magnetic permeability does not deteriorate, and are rather improved mainly by a promoted densification with very few pores and grain growth by sintering in high vacuum at a high temperature. It is also demonstrated that the fabricated alloy has excellent magnetic and mechanical properties compared to conventional sintered or compressed powder materials.

Нарушение закона броуновской релаксации для частиц феррита кобальта в воде

In the temperature range 0–90°C, the dynamic susceptibility of three samples of a magnetic fluid based on cobalt ferrite particles stabilized in water with a double layer of a surfactant was meas-ured. The first layer of the stabilizer was formed of auric acid molecules. The second layer consisted of a mixture of lauric acid and sodium dodecyl sulfate. The liquid samples had a small (about 10%) volume fraction of particles in order to reduce the influence of interparticle interactions and eliminate non-Newtonian rheological properties. The main parameter in which the samples differed was viscosity. It was changed by adding a small amount of polyvinyl alcohol. For all samples, in the studied temperature range the frequency dependence of the dynamic susceptibility had a quasi-Debye form with a pronounced maximum for the imaginary part. The value of the magnetization relaxation time was determined from the frequency of the maximum on the imaginary part of the dynamic susceptibility. As a result, the dependences of themagnetization relaxation time on tem-perature were obtained. To analyze the results obtained, viscosities of the samples were measured. All samples exhibited the properties of Newtonian fluids –the value of dynamic viscosity did not depend on the shear rate. The obtained results on the dynamic susceptibility and viscosity were compared by plotting relaxation times as a function of the ratio ofdynamic viscosity to absolute temperature. The resulting dependences do not fit on one universal straight line, as it is supposed to be according to the theory. The actual graph looks like a family of three different curves that di-verge as viscosity increases. In order to assess the influence of Néel relaxation on the resulting sus-ceptibility, the dynamic susceptibility of a frozen sample of the magnetic fluid was measured. The resulting susceptibility value was about 3% of the initial susceptibility of the liquid sample. Thus, despite the insignificant contribution of the Néel mechanism of magnetization relaxation to the dy-namic susceptibility, it is impossible to explain the obtained measurement results on the basis of the Brownian relaxation mechanism alone.

Design of a shelf pneumatic classifier for separating a polydisperse mixture of granulated superphosphate

The object of this study is a polydisperse mixture of granular superphosphate. It is emphasized that existing technologies of granulation and processing of granules lead to the formation of dusty fractions of small particles. The content of small fractions in the finished product should be minimal and, in connection with this problem, the task is to remove small particles from the mixture. The purpose of the current experimental study is to classify a polydisperse mixture of granular superphosphate in a pneumatic classifier. The device includes an inclined perforated shelf with an unloading space between its end and the wall of the apparatus. It has been experimentally revealed that the maximum efficiency of extraction into the entrainment of small particles is achieved with a width of the discharge space equal to 0.5 of the length of the cross-sectional side of the apparatus; the degree of perforation of the shelf is 5 %; the angle of inclination of the shelf is 25–30°; the speed of the gas flow in the free section of the apparatus is 3.7 m/s. It is shown that the degree of extraction into the entrainment of a small fraction less than 1 mm in size reaches 70–75 %, the content of the small fraction in the carry-over is 96–98 %, and the large fraction is less than 5 %. By processing experimental data, an empirical equation was built that makes it possible to determine the concentration of particles in the gas stream for individual fractions of the material. It is shown that due to the implementation of an active aerodynamic weighing mode, the shelf pneumatic classifier works at specific loads for air flow rate less than the typical designs of fluidized bed separators. It is noted that the effective operation of the shelf pneumatic classifier in the production of granular mineral fertilizers is ensured at a productivity of no more than 10–12 t/h. With greater productivity, there is a need to install several devices in the technological line

High-resolution multi-parameter monitoring of microbial water quality and particles at two alpine karst springs as a basis for an early-warning system

Karst aquifers are important resources for drinking water supply and are very vulnerable to contamination. Microbial concentrations at karst springs, in particular, often vary quickly over a short period of time. In this study, the response of microbial water quality and particle-size distribution of two alpine karst springs to rainfall events was investigated to test and validate parameters that can be used as early-warning systems for fecal contamination. At both investigated karst springs, total organic carbon, particle-size distribution (especially small particle fractions), and particle load show a good correlation to the fecal indicator bacteria E. coli and can therefore be used as a real-time indicator of fecal contamination at the investigated springs. In addition to conventional bacterial determination methods, the β-D-glucuronidase activity, which can be measured in near real-time, was used as a novel indicator parameter for fecal contamination. At the event scale, the β-D-glucuronidase (GLUC) activity shows a good correlation to E. coli and can be used as an additional real-time indicator of fecal contamination. For the studied springs, when they show two peaks in turbidity and small particles, these two parameters are suitable for an early warning system because the bacterial contamination occurs during the secondary peak of these parameters. These results highlight the vulnerability of karst aquifers and demonstrate the applicability of advanced measurement techniques in detecting fecal contamination in real-time, which is especially important given the time-consuming nature of conventional bacterial detection methods.

A Parameterization of Interstitial Aerosol Extinction and Its Application to Marine Cloud Brightening

Abstract Marine cloud brightening (MCB) is a geoengineering approach to counteract climate change by the deliberate seeding of sea salt aerosol particles that, once they activated to cloud droplets, directly increase cloud reflectance and hence global albedo. However, a large fraction of the seeded aerosol may remain interstitial, i.e., unactivated particles among cloud droplets. Because the consideration of interstitial aerosol optical properties usually requires computationally expensive simulations of the entire particle spectrum and direct Mie calculations, we develop a simple parameterization to be used with computationally efficient bulk and even bin cloud microphysical schemes that do not treat the unactivated aerosol explicitly. Using parcel and large-eddy simulations with highly detailed Lagrangian cloud microphysics and direct Mie calculations as a reference, we show that the parameterization captures the variability in the interstitial aerosol extinction successfully. By applying the parameterization to typical MCB cases, we find that the consideration of interstitial aerosol extinction is important for the assessment of MCB in shallow clouds with weak updrafts, in which only a small fraction of aerosol particles is activated to cloud droplets. Significance Statement The optical properties of clouds are not only determined by the number and size of cloud droplets. Unactivated aerosol particles, so-called interstitial aerosol, can contribute substantially to the optical thickness of shallow clouds with weak updrafts in aerosol-laden conditions. The consideration of interstitial aerosol optical thickness has been computationally challenging, but the new parameterization presented here allows for an efficient representation in various types of cloud models. The parameterization is shown to be an important addition for the assessment of marine cloud brightening (MCB), a potential geoengineering technique to counteract global warming by increasing the cloud albedo through the deliberate seeding of aerosol.

The velocity-dependent J-factor of the Milky Way halo: does what happens in the galactic bulge stay in the galactic bulge?

We consider the angular distribution of the photon signal which could arisefrom velocity-dependent dark matter annihilation within the Galactic bulge. We find that, for thecase of Sommerfeld-enhanced annihilation, dark matter annihilation within the bulge isdominated by slow speed particles which never leave the bulge, allowing one to find a simpleanalytic relationship between the dark matter profile within the Galactic bulge and the angulardistribution. On the other hand, for the case p- or d-wave annihilation, we find thatthe small fraction of high-speed particles which can leave the bulge provide a significant,often dominant, contribution to dark matter annihilation within the bulge. For these scenarios,fully understanding dark matter annihilation deep within the Galactic bulge, and the angular distribution ofthe resulting photon signal, requires an understanding ofthe dark matter profile well outside the bulge. We consider the Galactic Center excess inlight of these results, and find that an explanation of this excess in terms of p-waveannihilation would require the dark matter profile within the bulge to have a much steeperprofile than usually considered, but with uncertainties related to the behavior of the profileoutside the bulge.

Precipitation Evolution in the Heat‐Affected Zone and Coating Material of AA2024 Processed by Friction Surfacing

Herein, self‐mating coating depositions are generated from Al–Cu–Mg alloy AA2024 by using the solid‐state joining method, friction surfacing (FS). The precipitation evolution in the heat‐affected zone (HAZ) of the substrate material and in the deposited coatings is analyzed using hardness mapping, temperature measurements, differential scanning calorimetry (DSC), transmission electron microscopy (TEM) as well as synchrotron small‐angle X‐Ray scattering (SAXS) used for mapping mean particle radius and particle volume fraction over the whole sample. Quantitative measurements of the thermal cycle using thermocouples positioned inside the substrate sheets reveal a distinguishing temperature distribution and a maximum temperature up to 420 °C close to the center of the bonding zone (BZ). The hardness distribution is frequently encountered in solid‐state joining processes. It can be understood taking into account the complex modifications of the precipitate size distribution, including small Guinier–Preston–Bagaryatsky GPB (Al2CuMg)/Guinier–Preston GP(I) (Al2Cu)‐zones and larger S′ (Al2CuMg)/θ′ (Al2Cu)‐phases. Uniform precipitation of small and larger particles leads to an increase in hardness. It has become apparent that the highest hardness values within the HAZ are obtained when the volume fractions of small and larger particles are increased and equally distributed.

Influence of Addition of Ti Particles and Processing Condition on Microstructure and Properties of Selectively Laser-Melted Invar 36 Alloy.

Invar 36 exhibits extremely low thermal expansion coefficients at low temperatures but also low yield strength (YS), which greatly restricts its application as a structural material. In this study, a small fraction of pure titanium powder particles was added into Invar 36 by powder mixing and selective laser melting (SLM) with the aim of further improving tensile strengths of Invar 36. It was found that increased laser power led to increased grain size and to slight decrease in YS in Invar 36. During SLM, amorphous SiO2 nanoparticles were formed and homogeneously distributed in Invar 36. With the addition of 2 at% Ti powder particles, grains became larger and the crystallographic texture along <001> and <111> increased to some extent. Moreover, the bottom of solidified melt pools was segregated with Ti while the matrix was homogeneously decorated by a great number of nano-sized spherical Ti2O3 particles. These particles were found to have effectively impeded dislocation motion during plastic deformation, leading to significant improvement in 0.2% YS and ultimate tensile strength. The above precipitation led to consumption of a small amount of Ni from the matrix, which caused a minor compromise in thermal expansion properties. Nonetheless, the newly synthesized Invar 36-Ti alloy still exhibits low thermal expansion coefficients at low temperatures and remarkably enhanced tensile strengths.

Flame structure and burning velocity of flames propagating in binary iron aerosols

A numerical study was performed for binary dispersed iron aerosols in air using different particle sizes with constant average particle size. The effects of particle size and density of the two aerosols on flame structure and speed are systematically investigated. Varying the amount of small and big particles results in separated and overlapped flame fronts. For higher values of particle size ratio (ratio between the size of big and small particles) and density of small particles, flame fronts are observed to overlap. The flame speed of the binary mixture is compared with the mono-dispersed case and the difference is analyzed for different particle size ratios. The addition of a small fraction of small particles in the binary mixture is found to result in a substantial increase in the flame speed if the particle size ratio is large. Detailed analyses on the variation of the total amount of fuel shows the particle size ratio determines the equivalence ratio at which the maximum flame speed occurs. The maximum flame speed as a function of equivalence ratio was observed to move from the lean to the rich side for particle size ratio sufficiently large enough.

An experimental approach to investigate the viscoelastic and rheological behavior of polydisperse glass suspensions

Polydispersity is an essential factor in characterizing suspensions, specifically in industrial processes. In the present work, we report the viscosity of non-colloidal polydisperse glass suspensions for the first time and study the predictability of log-transformed quadratic viscosity equations over a wide range of blending ratios at a constant total volume fraction of solid particles. The viscosity and viscoelasticity measurement of multimodal suspensions was carried out by mixing three monomodally distributed solid particle suspensions with a relatively narrow size distribution to prepare bidisperse and tridisperse suspensions. The results showed a good agreement between experimental and predicted viscosity data for multimodal suspensions, making the generalized model a good alternative to describe the viscosity of polydisperse mixtures. The diameter ratio of large-to-small particles and the volume fraction of small particles in bidisperse systems strongly affected the viscoelastic behavior of multimodal suspensions. In addition, the dynamic rheology measurement showed that the storage modulus was independent of frequency, while a linear frequency dependence of loss modulus was observed for multimodal suspensions. In the case of polydisperse suspensions, this yield stress and dimensionless elastic modulus increased by declining the particle size ratio and increasing the volume fraction of small particles in bidisperse subsystems.

Effect of Post-Processing Heat Treatments on Short-Term Creep Response at 650 °C for a Ti-6Al-4V Alloy Produced by Additive Manufacturing

Post-processing heat treatments of Ti-6Al-4V parts produced by additive manufacturing are essential for restoring the peculiar martensitic structure that originates from the extremely high cooling rates typical of this technology. In this study, the influence of a 1050 °C annealing on a Ti-6Al-4V alloy, produced by additive manufacturing, on the minimum creep rate dependence on applied stress and temperature, was investigated at 650 °C. Experimental data obtained after two different subcritical annealings were also considered for comparison purposes. The analysis of the experimental creep data demonstrated that the alloy annealed at the highest temperature exhibited lower creep rates. The improved creep response was attributed to the combined effect of the presence of extended α-β interfaces and of a small volume fraction of Ti3Al particles.

Safety of zinc l-carnosine as a Novel food pursuant to Regulation (EU) 2015/2283 and the bioavailability of zinc from this source in the context of Directive 2002/46/EC on food supplements.

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver an opinion on zinc l‐carnosine as a novel food (NF) pursuant to Regulation (EU) 2015/2283 and as a source of zinc for use in food supplements. The NF is produced by chemical synthesis and is proposed to be used in food supplements as a source of zinc. The target population proposed by the applicant is individuals above the age of 12, excluding pregnant and lactating women. The NF which is the subject of the application is a chelate‐complex, formed between Zn2+ and l‐carnosine and is present as a mixture of a monomer and a dimer. The material is a powder with particulate nature and is insoluble in water at neutral pH. No relevant data using an existing zinc source as comparator have been made available by the applicant and the actual bioavailability of the zinc provided by the NF at the proposed use levels remains uncharacterised. Owing to the lack of a correct characterisation of the fraction of small particles, including nanoparticles of the NF, the Panel is not in the position to evaluate specification limits for the size of the constituent particles in the NF. Owing to the lack of information on the size distribution and the physico‐chemical properties of the particles constituting the NF, the Panel is not in the position to confirm whether the ADME studies and the toxicological studies provided by the applicant are appropriate to assess the safety of the NF. The Panel concludes that the NF is absorbed and provides zinc, but as it is in an insufficiently characterised particulate form, its safety has not been established and the bioavailability has not been determined.

Experimental Evaluation of Nanofluid for Improved Cooling Efficiency in an AL Mini Channel Heat Sink

Abstract: Efficient heat transfer has become major need these days. In this thesis, both experimental and CFD investigations have to be carried out to evaluate the cooling performance of a mini-channel consisting of fins on upper surface of flat plate. Nano fluids contain a small fraction of solid nano particles in base fluids flowing through groves in bottom plate attached with heater at base. Nano fluids cools small channel heat sinks, have been anticipated to be an excellent heat dissipation method for the next generation electronic devices. Computational Fluid Dynamics (CFD) simulations is to be carried out to study the heat sinks heat transfer mechanism. The sectional geometry of channels affects the flow and heat transfer characteristics of mini channel heat sinks. The heat transfer principle states that maximum heat transfer is achieved in mini channels with minimum pressure drop across it. In this research work the experimental and numerical investigation for the improved heat transfer characteristics of mini channel heat sink using Al2O3/water nano with (1 and 2 % volume fraction) fluid is to be done. The fluid flow characteristics are also analysed for the serpentine shaped mini channel. Heating element of 130 W capacities is to be used to heat up the heating element of base plate. Keywords: Heat, Fluids, Heating, Nano, Fraction, Flow, Sink, Channel, Plate, Aluminum.

Gel‐like inclusions of C‐terminal fragments of TDP‐43 sequester stalled proteasomes in neurons

Aggregation of the multifunctional RNA‐binding protein TDP‐43 defines large subgroups of amyotrophic lateral sclerosis and frontotemporal dementia and correlates with neurodegeneration in both diseases. In disease, characteristic C‐terminal fragments of ~25 kDa ("TDP‐25") accumulate in cytoplasmic inclusions. Here, we analyze gain‐of‐function mechanisms of TDP‐25 combining cryo‐electron tomography, proteomics, and functional assays. In neurons, cytoplasmic TDP‐25 inclusions are amorphous, and photobleaching experiments reveal gel‐like biophysical properties that are less dynamic than nuclear TDP‐43. Compared with full‐length TDP‐43, the TDP‐25 interactome is depleted of low‐complexity domain proteins. TDP‐25 inclusions are enriched in 26S proteasomes adopting exclusively substrate‐processing conformations, suggesting that inclusions sequester proteasomes, which are largely stalled and no longer undergo the cyclic conformational changes required for proteolytic activity. Reporter assays confirm that TDP‐25 impairs proteostasis, and this inhibitory function is enhanced by ALS‐causing TDP‐43 mutations. These findings support a patho‐physiological relevance of proteasome dysfunction in ALS/FTD.

Hydrodynamically Controlled Self-Organization in Mixtures of Active and Passive Colloids.

Active particles are known to exhibit collective behavior and induce structure in a variety of soft-matter systems. However, many naturally occurring complex fluids are mixtures of active and passive components. The authors examine how activity induces organization in such multi-component systems. Mixtures of passive colloids and colloidal micromotors are investigated and it is observed that even a small fraction of active particles induces reorganization of the passive components in an intriguing series of phenomena. Experimental observations are combined with large-scale simulations that explicitly resolve the near- and far-field effects of the hydrodynamic flow and simultaneously accurately treat the fluid-colloid interfaces. It is demonstrated that neither conventional molecular dynamics simulations nor the reduction of hydrodynamic effects to phoretic attractions can explain the observed phenomena, which originate from the flow field that is generated by the active colloids and subsequently modified by the aggregating passive units. These findings not only offer insight into the organization of biological or synthetic active-passive mixtures, but also open avenues to controlling the behavior of passive building blocks by means of small amounts of activeparticles.

Production and characterization of the Cr35Fe35V16.5Mo6Ti7.5 high entropy alloy

The microstructure, thermal stability, and mechanical properties of a novel Cr35Fe35V16.5Mo6Ti7.5 high-entropy alloy were studied. The mechanical properties were mapped by nanoindentation, and the results correlated with the microstructure and the Vickers microhardness measurements. The alloy was produced by arc melting in a low pressure He atmosphere. Thermal treatments were performed to study the thermal stability of the alloy. The as-cast microstructure of the alloy exhibited a body-centered cubic phase with morphology of dendrites, outlined by a very thin interdendritic phase with a crystallographic structure compatible with Fe2Ti. The presence of the intermetallic particles was predicted by a free-energy based model, in contrast with the single solid solution alloy predicted by a parameter-based model. The volume fraction of the dendrites in the alloy is ∼ 94 % after arc melting. A small fraction of sparse Ti-rich particles, ∼0.4 vol%, was observed. The thermal treatments produced an increase of the population of Ti-rich particles, the formation of a σ-phase and nucleation of precipitates enriched with Fe and Ti into the previous dendrites. The material in as-cast condition exhibited a microhardness value of 6.2 ± 0.3 GPa, while the alloy aged at 960 °C resulted in 7.1 ± 0.4 GPa. Nanoindentations maps showed an excellent correlation with the microstructure, and their statistical analyses yielded a nanohardness mean value of 8.2 ± 0.4 GPa in the dendritic BCC regions of the as-cast and thermal treated samples and 14.1 ± 0.6 GPa for the σ-phase. The onset of the plastic behavior has been studied by analyzing the pop-in phenomenon observed in the nanoindentation loading curves. For the as-cast alloy, this analysis showed that the elastic-to-plastic transition seems to be triggered by dislocation nucleation. The alloy has a low thermal diffusivity in the measured temperature range that increases on increasing temperature.

Formation and suppression of secondary cracks in deposits of colloidal ellipsoids

Primary and secondary cracks often coexist in a dried colloidal deposit. While, primary cracks have been the focus of investigation in most of the theoretical and experimental studies, understanding the formation and time evolution of secondary cracks is scarce. In addition, secondary cracks at times are undesirable especially when used as a template in the nano-lithography. Therefore, a control over their formation and suppression is of high importance. We consider the drying of sessile drops containing colloidal ellipsoids on a solid substrate. The resulting coffee-ring-like deposit of ellipsoids is found to accompany primary cracks in the circumferential direction and secondary cracks in the radial direction. A systematic study is performed to understand the nucleation and propagation of cracks. Our experiments explicitly showed that the primary cracks always nucleate at the top surface of the deposit and then penetrate the interior of the deposit. However, in contrast, the secondary cracks always form at the bottom surface of the deposit, which is in contact with the solid substrate. The secondary cracks are found to form only when the deposit thickness exceeds a critical value. In addition, we discuss methods to completely suppress the formation of secondary cracks by (i) tuning the aspect ratio of the ellipsoidal particles, and (ii) incorporating a small fraction of spherical particles in the drying drop of ellipsoids prior to the evaporation experiments.

The number fraction of iron-containing particles affects OH, HO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; budgets in the atmospheric aqueous phase

Abstract. Reactive oxygen species (ROS), such as OH, HO2 and H2O2, affect the oxidation capacity of the atmosphere and cause adverse health effects of particulate matter. The role of transition metal ions (TMIs) in impacting the ROS concentrations and conversions in the atmospheric aqueous phase has been recognized for a long time. Model studies usually assume that the total TMI mass as measured in bulk aerosol or cloud water samples is distributed equally across all particles or droplets. This assumption is contrary to single-particle measurements that have shown that only a small number fraction of particles contain iron and other TMIs (FN,Fe&lt;100 %), which implies that also not all cloud droplets contain TMIs. In the current study, we apply a box model with an explicit multiphase chemical mechanism to simulate ROS formation and cycling in aqueous aerosol particles and cloud droplets. Model simulations are performed for the range of 1 % ≤ FN,Fe ≤ 100 % for constant pH values of 3, 4.5 and 6 and constant total iron mass concentration (10 or 50 ng per cubic meter of air). Model results are compared for two sets of simulations with FN,Fe&lt;100 % (FeN&lt;100) and 100 % (FeBulk). We find the largest differences between model results in OH and HO2 / O2- concentrations at pH = 6. Under these conditions, HO2 is subsaturated in the aqueous phase because of its high effective Henry's law constant and the fast chemical loss reactions of the O2- radical anion. As the main reduction process of Fe(III) is its reaction with HO2 / O2-, we show that the HO2 subsaturation leads to Fe(II) / Fe(total) ratios for FN,Fe&lt;100 % that are lower by a factor of ≤ 2 as compared to bulk model approaches. This trend is largely independent of the total iron concentration, as both chemical source and sink rates of HO2 / O2- scale with the iron concentration. We compare model-derived reactive uptake parameters γOH and γHO2 for the full range of FN,Fe. While γOH is not affected by the iron distribution, the calculated γHO2 values range from 0.0004 to 0.03 for FN,Fe = 1 % and 100 %, respectively. Implications of these findings are discussed for the application of lab-derived γHO2 in models to present reactive HO2 uptake on aerosols. We conclude that the iron distribution (FN,Fe) should be taken into account to estimate the ROS concentrations and oxidation potential of particulate matter that might be overestimated by bulk sampling and model approaches. Our study suggests that the number concentration of iron-containing particles FN,Fe may be more important than the total iron mass concentration in determining ROS budgets and uptake rates in cloud and aerosol water.