Growth Of Precipitate Particles Research Articles

Performance comparison of filtering methods on modelling and forecasting the total precipitation amount: a case study for Muğla in Turkey

Abstract Condensed water vapor in the atmosphere is observed as precipitation whenever moist air rises sufficiently enough to produce saturation, condensation, and the growth of precipitation particles. It is hard to measure the amount and concentration of total precipitation over time due to the changes in the amount of precipitation and the variability of climate. As a result of these, the modelling and forecasting of precipitation amount is challenging. For this reason, this study compares forecasting performances of different methods on monthly precipitation series with covariates including the temperature, relative humidity, and cloudiness of Muğla region, Turkey. To accomplish this, the performance of multiple linear regression, the state space model (SSM) via Kalman Filter, a hybrid model integrating the logistic regression and SSM models, the seasonal autoregressive integrated moving average (SARIMA), exponential smoothing with state space model (ETS), exponential smoothing state space model with Box-Cox transformation-ARMA errors-trend and seasonal components (TBATS), feed-forward neural network (NNETAR) and Prophet models are all compared. This comparison has yet to be undertaken in the literature. The empirical findings overwhelmingly support the SSM when modelling and forecasting the monthly total precipitation amount of the Muğla region, encouraging the time-varying coefficients extensions of the precipitation model.

Microstructural characterization of interrupted aging on an AA7050 aluminum alloy

Interrupted aging heat treatments are used to maximize the gain in mechanical properties in 7xxx aluminum alloys through the production of a microstructure with a high density of fine precipitates, which are homogeneously dispersed in the aluminum matrix. In an interrupted aging heat treatment, the first stage, at higher temperature, aims at creating sites for subsequent nucleation of precipitate particles, while the second stage, at lower temperature, aims at the nucleation and growth of precipitate particles. The Interrupted aging heat treatment has been increasingly studied because it confers resistance levels similar to, or even higher than conventional heat treatments (e.g. T6), in addition to producing a more stable microstructure. In this study, a microstructural characterization was carried out using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) in an AA7050 aluminum alloys that was submitted to aging heat treatments T7451, T6 and T6I4-65, seeking a better understanding of the microstructure produced in each heat treatment and the reasons of the gain in mechanical properties. The results indicated that the T6I4-65 interrupted aging heat treatment was the most efficient in creating sites for nucleation of phases in the aluminum matrix, when compared with other conditions, due to the higher density of particles of the phases η′, η and T, in addition to being the only condition to have GPII zones and S phase in its microstructure.

Numerical Study of the Dynamic, Thermodynamic and Microstructural Parameters of Convective Clouds

On the basis of a three-dimensional non stationary model of a convective cloud with detailed description of dynamic, thermodynamic and microphysical processes, numerical experiments were conducted to study the formation of parameters of convective clouds under unstable stratification of the atmosphere. Numerical experiments have been carried out to study the formation of convective processes in the atmosphere. The thermo hydrodynamic parameters in the zone of a thunderstorm cloud are determined, and regions with a vortex motion of air are identified. The main flows feeding the convective cloud in the mature stage are determined. Due to the means of visualization, the areas of formation and growth of precipitation particles are identified. In a three-dimensional form, the interaction of dynamic and thermodynamic processes is analyzed. The interaction of fields is manifested in the form of deformation of fields of thermodynamic parameters under the influence of dynamic processes. Trajectories of air streams around a cloud and the trajectories of drops in a cloud are determined. The results of numerical experiments confirm that dynamic processes significantly influence the formation of fields of thermodynamic parameters in the cloud, which also determine the course of microphysical processes and the nature of the growth of precipitation particles.

Influence of Cloud Condensation Nuclei on Orographic Snowfall

Abstract Pollution aerosols acting as cloud condensation nuclei (CCN) have the potential to alter warm rain clouds via the aerosol first and second indirect effects in which they modify the cloud droplet population, cloud lifetime and size, rainfall efficiency, and radiation balance from increased albedo. For constant liquid water content, an increase in CCN concentration (NCCN) tends to produce an increased concentration of droplets with smaller diameters. This reduces the collision and coalescence rate, and thus there is a local reduction in rainfall. While this process applies to warm clouds, it does not identically carry over to mixed-phase clouds in which crystal nucleation, crystal riming, crystal versus droplet fall speed, and collection efficiency play active roles in determining precipitation amount. Sulfate-based aerosols serve as very efficient cloud nuclei but are not effective as ice-forming nuclei. In clouds where precipitation formation is dominated by the ice phase, NCCN influences precipitation growth by altering the efficiency of droplet collection by ice crystals and the fall trajectories of both droplet and crystal hydrometeors. The temporal and spatial variation in both crystal and droplet populations determines the resultant snowfall efficiency and distribution. Results of numerical simulations in this study suggest that CCN can play a significant role in snowfall production by winter, mixed-phase, cloud systems when liquid and ice hydrometeors coexist. In subfreezing conditions, a precipitating ice cloud overlaying a supercooled liquid water cloud allows growth of precipitation particles via the seeder–feeder process, in which nucleated ice crystals fall through the supercooled liquid water cloud and collect droplets. Enhanced NCCN from sulfate pollution by fossil fuel emissions modifies the droplet distribution and reduces crystal riming efficiency. Reduced riming efficiency inhibits the rate of snow growth, producing lightly rimed snow crystals that fall slowly and advect farther downstream prior to surface deposition. Simulations indicate that increasing NCCN along the orographic barrier of the Park Range in north-central Colorado results in a modification of the orographic cloud such that the surface snow water equivalent amounts are reduced on the windward slopes and enhanced on the leeward slopes. The inhibition of snowfall by pollution aerosols (ISPA) effect has significant implications for water resource distribution in mountainous terrain.

Vertical radar reflectivity profiles in Slovenia

Radar reflectivity from hydrometeors is used for the estimation of the precipitation rate at ground level. If the vertical reflectivity profile is taken into account, the estimate can be improved considerably. In the first part of the article some theoretical explanations are given for the two most pronounced characteristic of the vertical radar reflectivity profile from clouds. In general, the observed values decrease with height in the upper part of the radar echo due to the growth of precipitation particles by collision and coalescence. The effect of the bright band, especially in more stratiform types of precipitation, adds a significant strong peak to the profile, at the approximate height of the 0 °C isotherm. These explanations, although being simplified, also provide a quantitative explanation of the two characteristics mentioned previously. Averaged seasonal characteristics of vertical profiles in Slovenia are used as the climatological basis for the construction of an idealised profile for correcting the precipitation estimate. For individual cases, and also after averaging, a maximum in the profiles can clearly be detected. This maximum is much sharper if the profiles are normalised. When looking at time changes, it is shown that most of the changes in radar reflectivity, on average, occur during a roughly 6-hour time-lag between the two measurements. With greater time-lags, the differences are smaller on average. This is caused by the local natural evolution of the precipitation field and indicates that a 6-hour to 12-hour accumulating and averaging of data could diminish much of the error due to the time variation in radar estimated precipitation.

Coarsening behavior of γ″ precipitates in modified inconel 718 superalloy

The growth of precipitate particles in precipitation-hardened alloys is very significant, because it can control the long-time mechanical properties of these alloys. The kinetics of this coarsening process have been accounted for in the theory of diffusion-controlled growth, based on the growth theory of Lifshitz and Slyozov and Wagner. The growth of {gamma}{prime} precipitate particles, which have an ordered fcc structure and precipitate coherently in many Ni-containing fcc alloys, follows the d {proportional_to} t{sup 1/3} law. Another commonly observed strengthening phase in many nickel alloys is {gamma}{double_prime}, which has a bct structure and precipitates coherently with a disk shape. A well-known example of this class of alloy, is the widely used commercial alloy, Inconel 718. Here, the measured coarsening kinetics of separate precipitation of {gamma}{double_prime} is found to be linearly related to the cube root of the aging time at 700 and 730 C. However, the coarsening behavior of {gamma}{double_prime} in a compact morphology of {gamma}{prime} + {gamma}{double_prime} in the modified alloy is different from that of Inconel 718. Initially the coarsening rate is very slow, but eventually it coarsens rapidly. The actual {gamma}{double_prime} particle size distribution of the modified alloy is skewed towards large particle size and differs significantlymore » from the theoretically predicted distribution. TEM observations also confirm the preferential dissolution of {gamma}{double_prime} during coarsening, which could be attributed to the presence of an easy-diffusion path or lies to in a short-circuit diffusion.« less

Annealing and Precipitation in Iron–1.23 wt.-% Copper

Abstract Structural changes occurring during annealing and precipitation in cold-worked iron–1.23 wt.-% copper have been followed by transmission electron micro-scopy. After recovery at 600° C spherical precipitates are observed on dislocations and at sub-boundaries, the size and distribution of precipitates being related to the dislocation density and size of individual sub-grains. Growth of precipitate particles is thought to be assisted by mobile line and planar defects acting as collectors. On annealing at 750° C with a slow heating rate, the time for complete recrystallization is greater than when the heating rate is rapid owing to atmosphere locking of dislocations. The heating rate has a marked effect on the shape of precipitates, slow heating producing spheres while fast heating, in which less precipitate growth occurs when substructures are present, results in rods.

Precipitation in the system Al-0.05 wt pct Fe

The precipitation reaction in an aluminum alloy containing 0.05 wt pct Fe (enriched in Fe57) was studied using Mossbauer spectroscopy. It was found that in addition to the equilibrium precipitate, Fe Al3, the metastable phase FeAl6 occurs as well. Formation of FeAl6 is favored when the rate of precipitation is accelerated by cold working the supersaturated alloy. Step anneal experiments were performed in an effort to determine an activation energy for growth of precipitate particles. The results of these experiments are not entirely consistent with simple models of the nucleation and growth process.

A kinetic theory of nucleation in dilute solid solutions; Application to the precipitation of carbon and nitrogen in α-iron

A kinetic theory of nucleation and growth of precipitate particles in solid solutions is derived. This theory, which is applicable at low solute concentration and rather low solute-solute binding energy, is obtained by application of equilibrium conditions to the reversible chemical rate equations of cluster formation. The equilibrium approximation permits sufficient cancellation of terms in the equations so that the remaining equations are integrable. Computer solutions for a variety of parameters of the kinetic equations were used to check the range of validity of the approximation necessary to obtain the analytic expression. The analytic expression describes the experimentally observed time dependence of the precipitation of carbon and nitrogen in α-iron. The analytic theory also predicts an average binding energy of precipitate atoms in a cluster which is in reasonable agreement with experimentally derived carbon-carbon and nitrogen-nitrogen binding energies in iron. The size of the fundamental precipitate nucleus, as well as the distribution of sizes of precipitate particles, is also predicted, but no experiments exist to check these predictions.