Size Distribution Of Precipitated Particles Research Articles

Understanding the Global Three-dimensional Distribution of Precipitation Mean Particle Size with the Global Precipitation Measurement Mission

AbstractThis study addresses the global distribution of precipitation mean particle size using data from the Global Precipitation Measurement (GPM) mission. The mass-weighted mean diameter, Dm, is a characteristic parameter of the precipitation particle size distribution (PSD), estimated from the GPM Combined Radar-Radiometer Algorithm (CORRA) using data from GPM’s dual-frequency precipitation radar and microwave imager. We examine Dm in individual precipitation systems in different climate regimes and investigate a six-year (2014-2020) global climatology within 70° N/S.The vertical structure of Dm is demonstrated with cases of deep convection, frontal rain and snow, and stratocumulus light rain. The Dm values, detectable by GPM, range from ~0.7 mm in stratocumulus precipitation to >3.5 mm in the ice layers of intense convection. Within the constraint of the 12-dBZ detectability threshold, the smallest annual mean Dm (~ 0.8 mm) are found in the eastern oceans, and the largest values (~ 2 mm) occur above the melting levels in convection over land in summer. The standard deviation of the annual mean is generally < 0.45 mm below 6 km.Climate regimes are characterized with Dm annual/seasonal variations, its convective/stratiform components, and vertical variabilities (2-10 km). The US Central Plains and Argentina are associated with the largest Dm in a deep layer. Tropical Africa has larger Dm and standard deviation than Amazon. Large convective Dm occurs at high latitudes of Eurasia and North America in summer; the southern hemisphere high latitudes have shallower systems with smaller Dm. Oceanic storm tracks in both hemispheres have relatively large Dm, particularly for convective Dm in winter. Relatively small Dm occurs over tropical oceans, including ITCZ, requiring further investigation.

Corrections of Precipitation Particle Size Distribution Measured by a Parsivel OTT2 Disdrometer under Windy Conditions in the Antisana Massif, Ecuador

Monitoring precipitation in mountainous areas using traditional tipping-bucket rain gauges (TPB) has become challenging in sites with strong variations of air temperature and wind speed (Ws). The drop size distributions (DSD), amount, and precipitation-type of a Parsivel OTT2 disdrometer installed at 4730 m above sea level (close to the 0 °C isotherm) in the glacier foreland of the Antisana volcano in Ecuador are used to analyze the precipitation type. To correct the DSDs, we removed spurious particles and shifted fall velocities such that the mean value matches with the fall velocity–diameter relationship of rain, snow, graupel, and hail. Solid (SP) and liquid precipitation (LP) were identified through −1 and 3 °C thresholds and then grouped into low, medium, and high Ws categories by k-means approach. Changes in DSDs were tracked using concentration spectra and particle’s contribution by diameter and fall velocity. Thus, variations of concentration/dispersion and removed hydrometeors were linked with Ws changes. Corrected precipitation, assuming constant density (1 g cm−3), gives reliable results for LP with respect to measurements at TPB and overestimates SP measured in disdrometer. Therefore, corrected precipitation varying density models achieved fewer differences. These results are the first insight toward the understating of precipitation microphysics in a high-altitude site of the tropical Andes.

Measurement and Modeling of the Precipitation Particle Size Distribution

Precipitation plays a vital role within the Earth system [...]

Winter precipitation particle size distribution measurement by Multi-Angle Snowflake Camera

From the radar meteorology viewpoint, the most important properties for quantitative precipitation estimation of winter events are 3D shape, size, and mass of precipitation particles, as well as the particle size distribution (PSD). In order to measure these properties precisely, optical instruments may be the best choice. The Multi-Angle Snowflake Camera (MASC) is a relatively new instrument equipped with three high-resolution cameras to capture the winter precipitation particle images from three non-parallel angles, in addition to measuring the particle fall speed using two pairs of infrared motion sensors. However, the results from the MASC so far are usually presented as monthly or seasonally, and particle sizes are given as histograms, no previous studies have used the MASC for a single storm study, and no researchers use MASC to measure the PSD. We propose the methodology for obtaining the winter precipitation PSD measured by the MASC, and present and discuss the development, implementation, and application of the new technique for PSD computation based on MASC images. Overall, this is the first study of the MASC-based PSD. We present PSD MASC experiments and results for segments of two snow events to demonstrate the performance of our PSD algorithm. The results show that the self-consistency of the MASC measured single-camera PSDs is good. To cross-validate PSD measurements, we compare MASC mean PSD (averaged over three cameras) with the collocated 2D Video Disdrometer, and observe good agreements of the two sets of results.

The impact of polymeric excipients on the particle size of poorly soluble drugs after pH-induced precipitation

Active pharmaceutical ingredients (APIs) with strongly pH-dependent aqueous solubility can face the problem of precipitating from solution when the pH changes from acidic in the stomach to neutral in the intestine. The present work investigates the effect of two polymeric excipients – polyvinylpyrrolidone (PVP) and Soluplus – on the ability to either prevent precipitation, or to control the size distribution of precipitated particles when precipitation cannot be prevented. Two different APIs were compared, Dabigatran etexilate mesylate and Rilpivirine hydrochloride. The effect of excipient concentration on the precipitation behaviour during pH titration was systematically investigated and qualitatively different trends were observed: in case of Soluplus, which forms a micellar solution when critical micelle concentration is exceeded, precipitation was inhibited in the case of Dabigatran etexilate, which partitioned into the micelles. On the other hand, Rilpivirine precipitated independently of Soluplus concentration. In the case of PVP, which does not form micelles, precipitation could not be avoided. Increased polymer concentration, however prevented the aggregation of precipitated particles into larger cluster. The observed effect of PVP was especially pronounced for Rilpivirine. The main conclusion of this study is that a suitably chosen polymeric excipient can either prevent precipitation altogether or reduce the size of the resulting particles. The mechanism of action, however, seems-specific to a given molecule. It was also shown that the polymer-stabilised particles have a potential to redissolve.

Modelling and Simulation of Particle Size Distribution of Precipitates in Continuous Tubular Crystallizers

This paper presents a population balance model for describing the temporal evolution of the particle size distribution of a precipitate produced in a laboratory scale tubular crystallizer, including nucleation, growth and agglomeration of crystals. The quadrature method of moments is used to calculate the moments of the crystal size distribution. The gamma probability density function with the sixth order Laguerre polynomials are used to reproduce the particle size distribution from moments. A sensitivity analyses is carried out by simulation that can be helpful when designing a crystallizer. Influence of the design and process parameters on the particle size distribution of product is analysed.

Influence of Formulation and Processing Variables on Properties of Itraconazole Nanoparticles Made by Advanced Evaporative Precipitation into Aqueous Solution

Nanoparticles, of the poorly water-soluble drug, itraconazole (ITZ), were produced by the Advanced Evaporative Precipitation into Aqueous Solution process (Advanced EPAS). This process combines emulsion templating and EPAS processing to provide improved control over the size distribution of precipitated particles. Specifically, oil-in-water emulsions containing the drug and suitable stabilizers are sprayed into a heated aqueous solution to induce precipitation of the drug in form of nanoparticles. The influence of processing parameters (temperature and volume of the heated aqueous solution; type of nozzle) and formulation aspects (stabilizer concentrations; total solid concentrations) on the size of suspended ITZ particles, as determined by laser diffraction, was investigated. Furthermore, freeze-dried ITZ nanoparticles were evaluated regarding their morphology, crystallinity, redispersibility, and dissolution behavior. Results indicate that a robust precipitation process was developed such that size distribution of dispersed nanoparticles was shown to be largely independent across the different processing and formulation parameters. Freeze-drying of colloidal dispersions resulted in micron-sized agglomerates composed of spherical, sub-300-nm particles characterized by reduced crystallinity and high ITZ potencies of up to 94% (w/w). The use of sucrose prevented particle agglomeration and resulted in powders that were readily reconstituted and reached high and sustained supersaturation levels upon dissolution in aqueous media.

Effect of antiscalant degradation on salt precipitation and solid/liquid separation of RO concentrate

The key limitation to the application of reverse osmosis (RO) desalination on inland brackish waters is concentrate disposal. Due to precipitation of sparingly soluble salts (CaCO 3, CaSO 4, BaSO 4, SrSO 4), RO membrane recovery cannot be increased further; therefore, other strategies must be investigated. Antiscalants are often added to RO feed water to help prevent precipitation and increase RO recovery, but in concentrate treatment, antiscalants may prevent precipitation of problematic constituents. A three-stage process to treat brackish water RO concentrate was investigated; the stages include oxidation of antiscalants with ozone and hydrogen peroxide, precipitation at elevated pH, and solid/liquid separation. A model water concentrate was used to perform laboratory scale experiments for each treatment stage. Experimental results showed that the advanced oxidation process (AOP) of ozonation and hydrogen peroxide on phosphonate antiscalants allowed increased calcium precipitation as well as loss of the solubilizing effects of antiscalants as compared to precipitation without prior ozonation of the antiscalants. The AOP also removed the effect of antiscalant on precipitate particle size distribution and particle morphology. In some cases, the AOP also improved microfiltration performance for the solid/liquid separation stage. The concentrate treatment could increase overall recovery from 80% to 90% for non-ozonated, antiscalant-dosed concentrate and from 80% to 94% for ozonated, antiscalant-dosed concentrate.

Modelling and characterization of chi-phase grain boundary precipitation during aging of Fe–Cr–Ni–Mo stainless steel

High molybdenum stainless steels may contain the chi-phase precipitate ( χ, Fe 36Cr 12Mo 10) which may lead to undesirable effects on strength, toughness and corrosion resistance. In the present work, specimens of a 12Cr–9Ni–4Mo wt% steel are heat treated at different temperatures and times, and the average particle size and particle size distribution of chi-phase precipitate are studied quantitatively. A computer model based on the KWN framework has been developed to describe the evolution of chi-phase precipitation. The kinetic model takes advantage of the KWN model to describe the precipitate particle size distribution, and is coupled with the thermodynamic software ThermoCalc ® for calculating the instantaneous local thermodynamic equilibrium condition at the interface and the driving force for nucleation. A modified version of Zener's theory accounting for capillarity effects at early growth stages is implemented in this model. The prediction of the model for chi-phase precipitation at a grain boundary is compared to experimental results and both the average particle size and the particle size distribution are found to be in good agreement with experimental observations at late precipitation stages.

Steady State Size Distribution of Asphaltenes by Flocculation From Toluene–n-Heptane Mixtures

The aggregation mechanisms of asphaltenes have been the subject of several recent studies. In this work, we have studied the effect of inhibitors on size distribution of asphaltene particles, in solutions containing toluene and mixtures of n-heptane and toluene. The asphaltenes used have been extracted from Marlim crude oil, using a modified procedure IP-143/82. Several solutions containing one percent volume of asphaltenes have been prepared in pure toluene and in toluene and n-heptane mixtures with and without inhibitors and have been homogenized during a period of 24 h. The particles sizes were determined by filtering the solutions through a set of standard filters ranging from 0.45 to 0.02 µm pore size. In addition, from the saturated filtered solution of asphaltene in toluene, three other solutions were prepared having 10, 20, and 30% volume of n-heptane and were homogenized for 24 h. Again the size distribution of precipitated particles was obtained by filtering. The concentration of asphaltenes remaining in the solution was measured directly by evaporation or by spectroscopy. The results have shown that large part of asphaltenes remain as colloidal particles in the size range tested in toluene solution without inhibitor. On the solutions in which inhibitors were used, one of the inhibitors effectively prevented flocculation, concentrating the asphaltene particles on the smaller size range even on mixtures containing 20 and 30% volume of n-heptane, which is a strong flocculating agent.

Prediction of the size distribution of precipitates

Modelling has proven to be an efficient way of cutting the time and costs associated with the investigation of materials properties. A new mathematical model for the prediction of the particle size distribution of precipitates has been developed. The model allows the description of all stages of the precipitation process: nucleation, growth and Ostwald ripening of particles. The incorporation of existing thermodynamic databases allows the simulation of a formation of dispersed phases in commercial multicomponent alloys.The influence of the model parameters on the final particle size distribution was investigated with the example of NbC formation in austenite. It was shown that the interfacial energy of a particle‐matrix interface has the most significant effect on the final particle arrangement. A pre‐exponential factor, which is the subject of nucleation theories, plays a less significant role in the final particle arrangement.

Precipitate particle size distribution in rigid and floppy networks

It is a usual assumption that oxide glasses build up continuous random networks. A further and very important development of this approach is the rigidity networks idea. According to it, the network switches from floppy to rigid if the number of bridges between the network formers exceeds a certain threshold value. In oxide glasses, only properties which require a motion over a sufficiently large distance will be subject to angular constraints at oxygen bonds thus there can be a switch from floppy to rigid modes. The kinetics of phase transition (and most nucleation processes) are very sensitive to the rigidity of the network. Slightly above the threshold concentration of rigid bonds some tiny floppy regions still exist inside the rigid network. They can serve as active centers for the nucleation process. Much later, nucleation can appear in the rigid part of the network. Therefore, we predict a certain interval of concentration of rigid bonds in which a bimodal size distribution function of precipitated particle will be observed. This prediction is confirmed by experimental data.

Preparation of homogeneous microspheres for optical cavity

Using phenyltriethoxysilane (PTES) as a starting material, preparation of pore-free organic–inorganic hybrid spheres of micrometer sizes have been investigated for their application to optical cavities. Undesirable imperfections such as inside pores which scatter light decrease the quality factor ( Q value) of a sphere. Centrifugation technique using potassium tartrate aqueous solution as a density-changing solvent from 1.0 to 1.4 was developed to separate pore-free particles from as-prepared particles. The percentage of pore-free particles was estimated about 5% of the weight of as-prepared samples. The size distribution of precipitated particles in various density solvents was estimated by scanning electron micrograph. Larger density, pore-free particles had a smaller size compared with those of low density, pore-containing spheres.

A small-angle X-ray scattering study of late-stage δ′ precipitation in Al-7.9%Li alloy for growth kinetics and dynamic scaling

A modified method for small-angle X-ray scattering (SAXS) analysis was developed to reconstruct the free-form particle size distribution of precipitates by including the interparticle interference effect. In this paper, the known indirect Fourier transform method (ITM) is extended to include the hard-sphere (HS) model which considers the interaction between the precipitates. This method is tested by analyzing simulated SAXS data and shows a better agreement than other similar studies. Then this modified method is applied to analyze several experimental SAXS data from δ′ (Al 3Li particles) precipitation in Al-7.9at%Li alloys aged at various conditions. The variation of average radii with aging time was found to follow the kinetic power law. The SAXS results are used to investigate the kinetic model of the δ′ coarsening (Ostwald ripening) with volume fraction effect. When comparing both experimentally obtained asymptotic size distributions of δ′ particles with those predicted by the kinetic theories, the MLSW theory is found to be in better agreement with the experimental results. This work gives a more clear interpretation of the coarsening mechanism than other experimental results. The dynamic scaling behavior of this phase separation is also investigated.

A new theoretical formulation for calculation of the specific attenuation due to precipitation particles on terrestrial and satellite radio links

The propagation of high frequency electromagnetic waves through rain is affected by absorption and scattering, which both lead to signal attenuation on satellite or terrestrial super high frequency (SHF) and extremely high frequency (EHF) links. Many factors govern rain effects on waves propagating in the atmosphere, namely raindrop size distribution, rain cumulative distribution, water temperature, refractive index and operating frequency. A high degree of accuracy in the calculation of specific attenuation caused by rain (attenuation per km) is of importance when planning high frequency radio communication systems. Until now, the kR α expression has been widely used for such calculations. This relationship in which R (mm/h) represents the rain rate, α and k parameters determined for each frequency by interpolation, can be considered to be a compromise between the complexity and a simplified approach of the Van de Hulst relationship. In this paper, we present a new theoretical model based on physical laws and allowing the calculation of specific attenuation caused by all kinds of hydrometeor particles on high frequency electromagnetic waves. This method, which we derived from the forward scattering amplitude and the Van de Hulst relationship, is governed by wave polarization, the wave incidence angle, the radio link operating frequency, and precipitation particle size distribution in the climate of interest. Its application gives theoretical results which are in very good agreement with data gathered on terrestrial or earth-satellite links in several localities around the world. This new proposed model can be easily used and will constitute a very useful tool for evaluating satellite and terrestrial radio link performances, mainly in the future which will bring an expansion of high frequency satellite systems.

The effect of fluid-jet mixing on protein precipitate growth during low-frequency conditioning

The mixing effects of low-frequency conditioning during protein precipitate aggregation are investigated. The conditioning process is described on the basis of a jet-mixing phenomena with aggregation being enhanced by the mixing effect of a fluid jet formed during vibration. The mixing performance is shown to correlate with the frequency of formation and the amplitude of the fluid jet. This amplitude is determined by the response of the conditioning system to a pulse or disturbance and is, for a particular suspending fluid, a function of the geometry of the outlet pipe of the conditioning chamber. The fluid-jet acceleration determines the break-up or prevention of formation of large precipitate aggregates. Improvements in the precipitate particle size distribution are related to the extent of fluid-jet mixing which promotes the removal of fine particles by aggregation with larger particles. Maxima are observed in particle size enhancement as a function of the fluid-jet acceleration with up to 40% increase in particle size at the fine end of the cumulative size distribution.

The effects of micromixing and the manner of reactor feeding on precipitation in stirred tank reactors

The effect of micromixing on the course of a precipitation process involving instantaneous irreversible chemical reaction (of the type: A + B → C) between two ionic solutions snd subsequent crystallization of the product is considered. It is demonstrated that the micromixing intensity and the manner of reactor feeding (batch or continuous, premixed or unpremixed feed system) are major factors affecting the precipitation process and the resulting size distribution of precipitated particles. The method of prediction of these effects is based on a micromixing model, which is related to the theory of turbulent mixing in an isotropic, homogeneous turbulent field.

A new example for the applicability of the relationship between the particle size and the kinetic of the crystal growth

AbstractExperiments have been made with PbCrO4 precipitating system in a batch type tank. In the experiments the speeds of stirring and the residence times were changed. The particle size distribution of precipitates formed has been determined. The rate determining mechanism of the crystal growth were evaluated by two different methods (NIELSEN method and method elaborated in our institute). The two methods used have indicated the same informations about the rate determining processes. It also has been stated that the coagulation does not disturb the selection of the suitable growing mechanism.