scholarly journals Modeling and Simulation of Pore Formation in a Bainitic Steel During Creep

2022 ◽  
Author(s):  
Felix Meixner ◽  
Mohammad Reza Ahmadi ◽  
Christof Sommitsch
Keyword(s):  
High Pressures ◽  
Elevated Temperatures ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Number Density ◽  
Creep Cavitation ◽  
Creep Resistant Steels ◽  
The Many ◽  
Modified Forms ◽  
Good Agreement

AbstractIn the field of power engineering, where materials are subjected to high pressures at elevated temperatures for many decades, creep-resistant steels are put to work. Their service life is still, however, finite, as the many changes in their microstructure can merely be mitigated and not avoided. Creep cavitation is one of those changes and, in many cases, ultimately causes failure by rupture. In this work, a model is proposed to simulate the nucleation and growth of cavities during creep. This exclusively physics-based model uses modified forms of Classical Nucleation Theory and the Onsager Extremum Principle in a newly developed Kampmann–Wagner framework. The model is validated on P23 steel which underwent creep rupture experiments at 600 °C and stresses of 50, 70, 80, 90 and 100 MPa for creep times up to 46000 hours. The model predicts qualitatively the shape and prevalence of cavities at different sites in the microstructure, and quantitatively the number density, size of cavities and their phase fraction contributing to a reduction in density. Finally, we find good agreement between the simulation and the experimental results especially at low stresses and longer creep times.

scholarly journals Efficiency of immersion mode ice nucleation on surrogates of mineral dust

2007 ◽  
Vol 7 (19) ◽  
pp. 5081-5091 ◽  
Author(s):  
C. Marcolli ◽  
S. Gedamke ◽  
T. Peter ◽  
B. Zobrist
Keyword(s):  
Contact Angle ◽  
Active Sites ◽  
Quantitative Agreement ◽  
Ice Nucleation ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Aqueous Suspensions ◽  
Freezing Temperatures ◽  
Good Agreement ◽  
Heterogeneous Ice Nucleation

Abstract. A differential scanning calorimeter (DSC) was used to explore heterogeneous ice nucleation of emulsified aqueous suspensions of two Arizona test dust (ATD) samples with particle diameters of nominally 0–3 and 0–7 μm, respectively. Aqueous suspensions with ATD concentrations of 0.01–20 wt% have been investigated. The DSC thermograms exhibit a homogeneous and a heterogeneous freezing peak whose intensity ratios vary with the ATD concentration in the aqueous suspensions. Homogeneous freezing temperatures are in good agreement with recent measurements by other techniques. Depending on ATD concentration, heterogeneous ice nucleation occurred at temperatures as high as 256 K or down to the onset of homogeneous ice nucleation (237 K). For ATD-induced ice formation Classical Nucleation Theory (CNT) offers a suitable framework to parameterize nucleation rates as a function of temperature, experimentally determined ATD size, and emulsion droplet volume distributions. The latter two quantities serve to estimate the total heterogeneous surface area present in a droplet, whereas the suitability of an individual heterogeneous site to trigger nucleation is described by the compatibility function (or contact angle) in CNT. The intensity ratio of homogeneous to heterogeneous freezing peaks is in good agreement with the assumption that the ATD particles are randomly distributed amongst the emulsion droplets. The observed dependence of the heterogeneous freezing temperatures on ATD concentrations cannot be described by assuming a constant contact angle for all ATD particles, but requires the ice nucleation efficiency of ATD particles to be (log)normally distributed amongst the particles. Best quantitative agreement is reached when explicitly assuming that high-compatibility sites are rare and that therefore larger particles have on average more and better active sites than smaller ones. This analysis suggests that a particle has to have a diameter of at least 0.1 μm to exhibit on average one active site.

Analytical Investigation on the Homogeneous Nucleation in a Mono-Component and Bi-Component Droplet

2019 ◽  
Author(s):  
Xi Xi ◽  
Hong Liu ◽  
Chang Cai ◽  
Ming Jia ◽  
Weilong Zhang
Keyword(s):  
Nucleation Rate ◽  
Homogeneous Nucleation ◽  
Ambient Pressure ◽  
Analytical Investigation ◽  
Bubble Nucleation ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Liquid Temperature ◽  
Wide Range ◽  
Good Agreement

Abstract The work attempts to analyze the performance of homogeneous nucleation by using the non-equilibrium thermodynamics theory and the classical nucleation theory. A nucleation rate graph was constructed under a wide range of operating temperature conditions. The results indicate that the superheat limit temperature (SLT) estimated by the modified homogeneous nucleation sub-model is in good agreement with the experimental results. The nucleation rate increases exponentially with the liquid temperature rise when the liquid temperature exceeds the SLT under atmospheric pressure. The superheated temperature needed to trigger the bubble nucleation decreases with the elevated ambient pressure.

scholarly journals Molecular dynamics simulations of liquid silica crystallization

2018 ◽  
Vol 115 (21) ◽  
pp. 5348-5352 ◽  
Author(s):  
Haiyang Niu ◽  
Pablo M. Piaggi ◽  
Michele Invernizzi ◽  
Michele Parrinello
Keyword(s):  
Free Energy ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Free Energy Surface ◽  
X Ray Diffraction ◽  
Collective Variables ◽  
Atomic Simulations ◽  
The Difference ◽  
Dynamics Simulations ◽  
Good Agreement

Silica is one of the most abundant minerals on Earth and is widely used in many fields. Investigating the crystallization of liquid silica by atomic simulations is of great importance to understand the crystallization mechanism; however, the high crystallization barrier and the tendency of silica to form glasses make such simulations very challenging. Here we have studied liquid silica crystallization to β-cristobalite with metadynamics, using X-ray diffraction (XRD) peak intensities as collective variables. The frequent transitions between solid and liquid of the biased runs demonstrate the highly successful use of the XRD peak intensities as collective variables, which leads to the convergence of the free-energy surface. By calculating the difference in free energy, we have estimated the melting temperature of β-cristobalite, which is in good agreement with the literature. The nucleation mechanism during the crystallization of liquid silica can be described by classical nucleation theory.

scholarly journals Efficiency of immersion mode ice nucleation on surrogates of mineral dust

2007 ◽  
Vol 7 (4) ◽  
pp. 9687-9716
Author(s):  
C. Marcolli ◽  
S. Gedamke ◽  
T. Peter ◽  
B. Zobrist
Keyword(s):  
Contact Angle ◽  
Active Sites ◽  
Quantitative Agreement ◽  
Ice Nucleation ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Aqueous Suspensions ◽  
Freezing Temperatures ◽  
Good Agreement ◽  
Heterogeneous Ice Nucleation

Abstract. A differential scanning calorimeter (DSC) was used to explore heterogeneous ice nucleation of emulsified aqueous suspensions of two Arizona test dust (ATD) samples with particle diameters of nominally 0–3 and 0–7 μm, respectively. Aqueous suspensions with ATD concentrations of 0.01–20 wt% have been investigated. The DSC thermograms exhibit a homogeneous and a heterogeneous freezing peak whose intensity ratios vary with the ATD concentration in the aqueous suspensions. Homogeneous freezing temperatures are in good agreement with recent measurements by other techniques. Depending on ATD concentration, heterogeneous ice nucleation occurred at temperatures as high as 256 K or down to the onset of homogeneous ice nucleation (237 K). For ATD-induced ice formation Classical Nucleation Theory (CNT) offers a suitable framework to parameterize nucleation rates as a function of temperature, experimentally determined ATD size, and emulsion droplet volume distributions. The latter two quantities serve to estimate the total heterogeneous surface area present in a droplet, whereas the suitability of an individual heterogeneous site to trigger nucleation is described by the compatibility function (or contact angle) in heterogeneous CNT. The intensity ratio of homogeneous to heterogeneous freezing peaks is in good agreement with the assumption that the ATD particles are randomly distributed amongst the emulsion droplets. The observed dependence of the heterogeneous freezing temperatures on ATD concentrations cannot be described by assuming a constant contact angle for all ATD particles, but requires the ice nucleation efficiency of ATD particles to be (log)normally distributed amongst the particles. Best quantitative agreement is reached when explicitly assuming that high-compatibility sites are rare and that therefore larger particles have on average more and better active sites than smaller ones. This analysis suggests that a particle has to have a diameter of at least 0.1 μm to exhibit on average one active site.

Precipitation of Niobium Carbonitrides: Chemical Composition Measurements and Modeling

2007 ◽  
Vol 539-543 ◽  
pp. 4196-4201 ◽  
Author(s):  
Michel Perez ◽  
Eglantine Courtois ◽  
Daniel Acevedo Reyes ◽  
Thierry Epicier ◽  
Philippe Maugis
Keyword(s):  
Chemical Composition ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Model Alloy ◽  
Numerical Resolution ◽  
Pure Niobium ◽  
Transmission Electron ◽  
Niobium Nitrides ◽  
Electron Energy Loss ◽  
Good Agreement

High Resolution Transmission Electron Microscope and Electron Energy Loss Spectroscopy and have been used to characterize the structure and chemical composition of niobium carbonitrides in the ferrite of a Fe-Nb-C-N model alloy at different precipitation stages. Experiments seem to indicate the coexistence of two types of precipitates: pure niobium nitrides and mixed sub-stoichiometric niobium carbonitrides. In order to predict the chemical composition of these precipitates, a thermodynamical formalism has been developed to evaluate (i) the nucleation and growth rates (classical nucleation theory) and (ii) the chemical composition of nuclei and existing precipitates. A model based on the numerical resolution of former equations, is used to compute precipitates size distribution evolution at a given temperature. The predicted compositions are in very good agreement with experimental results.

Classical Nucleation Theory and Its Application to Condensing Steam Flow Calculations

2005 ◽  
Vol 219 (12) ◽  
pp. 1315-1333 ◽  
Author(s):  
F Bakhtar ◽  
J B Young ◽  
A J White ◽  
D A Simpson
Keyword(s):  
Predictive Accuracy ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Droplet Radius ◽  
Droplet Growth ◽  
Wide Range ◽  
Recent Developments ◽  
Judicious Choice ◽  
The Many ◽  
Low Pressures

The paper discusses the classical theory of the homogeneous nucleation of water droplets from supersaturated vapour and its application in predicting condensation in steam nozzles. The first part consists of a review of classical nucleation theory, focusing on the many modifications made to the original Becker-Döring theory and providing some new insights into recent developments. It is concluded that the predictive accuracy required for engineering calculations is not yet attainable with a theory derived from first principles. The areas that require most attention relate to the properties of small molecular clusters and the energy transfer processes in the non-isothermal theory. Experiments in converging-diverging nozzles provide the best means for validation at the very high nucleation rates of interest, but measurements of pressure distribution and the Sauter mean droplet radius are insufficient to provide independent checks on the separate theories of nucleation and droplet growth. Nevertheless, a judicious choice for the nucleation rate equation, in combination with a standard droplet growth model and a suitable equation of state for steam, can provide accurate predictions over a wide range of conditions. The exception is at very low pressures where there is evidence that the droplet growth rate in the nucleation zone is underestimated.

scholarly journals Homogeneous nucleation rates of nitric acid dihydrate (NAD) at simulated stratospheric conditions – Part II: Modelling

2006 ◽  
Vol 6 (10) ◽  
pp. 3035-3047 ◽  
Author(s):  
O. Möhler ◽  
H. Bunz ◽  
O. Stetzer
Keyword(s):  
Nitric Acid ◽  
Process Model ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Diffusion Activation Energy ◽  
Interface Tension ◽  
Experimental Conditions ◽  
Microphysical Process ◽  
Aerosol Chamber ◽  
Good Agreement

Abstract. Activation energies ΔGact for the nucleation of nitric acid dihydrate (NAD) in supercooled binary HNO3/H2O solution droplets were calculated from volume-based nucleation rate measurements using the AIDA (Aerosol, Interactions, and Dynamics in the Atmosphere) aerosol chamber of Forschungszentrum Karlsruhe. The experimental conditions covered temperatures T between 192 and 197 K, NAD saturation ratios SNAD between 7 and 10, and nitric acid molar fractions of the nucleating sub-micron sized droplets between 0.26 and 0.28. Based on classical nucleation theory, a new parameterisation for ΔGact=A×(T ln SNAD)−2+B is fitted to the experimental data with A=2.5×106 kcal K2 mol−1 and B=11.2−0.1(T−192) kcal mol−1. A and B were chosen to also achieve good agreement with literature data of ΔGact. The parameter A implies, for the temperature and composition range of our analysis, a mean interface tension σsl=51 cal mol−1 cm−2 between the growing NAD germ and the supercooled solution. A slight temperature dependence of the diffusion activation energy is represented by the parameter B. Investigations with a detailed microphysical process model showed that literature formulations of volume-based (Salcedo et al., 2001) and surface-based (Tabazadeh et al., 2002) nucleation rates significantly overestimate NAD formation rates when applied to the conditions of our experiments.

Homogeneous Bubble Nucleation Predicted by a Molecular Interaction Model

1991 ◽  
Vol 113 (3) ◽  
pp. 714-721 ◽  
Author(s):  
Ho-Young Kwak ◽  
Sangbum Lee
Keyword(s):  
Bubble Formation ◽  
Interaction Model ◽  
Bubble Nucleation ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Good Prediction ◽  
Evaporation Time ◽  
Modified Model ◽  
Superheat Limit ◽  
Good Agreement

The homogeneous bubble nucleation of various hydrocarbons was estimated by the modified classical nucleation theory. In this modification, the kinetic formalism of the classical theory is retained while the surface energy needed for the bubble formation is calculated from the interaction energy between molecules. With a nucleation rate value of Jnc =1022 nuclei/cm3s, this modified model gives a very good prediction of the superheat limit of liquids. In another test of the model the complete evaporation time of a butane droplet at its superheat limit is compared with experiments and found to be in good agreement.

scholarly journals Homogeneous nucleation rates of nitric acid dihydrate (NAD) at simulated stratospheric conditions – Part II: Modelling

2006 ◽  
Vol 6 (2) ◽  
pp. 2119-2149 ◽  
Author(s):  
O. Möhler ◽  
H. Bunz ◽  
O. Stetzer
Keyword(s):  
Nitric Acid ◽  
Process Model ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Diffusion Activation Energy ◽  
Experimental Conditions ◽  
Microphysical Process ◽  
Aerosol Chamber ◽  
Diffusion Activation ◽  
Good Agreement

Abstract. Activation energies ΔGact for the nucleation of nitric acid dihydrate (NAD) in supercooled binary HNO3/H2O solution droplets were calculated from volume-based nucleation rate measurements using the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) aerosol chamber of Forschungszentrum Karlsruhe. The experimental conditions covered temperatures T between 192 K and 197 K, NAD saturation ratios SNAD between 7 and 10, and nitric acid molar fractions of the nucleating sub-micron sized droplets between 0.26 and 0.28. Based on classical nucleation theory, a new parameterisation ΔGact=A×(T lnSNAD)-2+B is fitted to our experimetnal data with A=2.5×106 kcal K2 mol-1 and B=11.2−0.1(T−192) kcal mol-1. A and B were chosen to also achieve good agreement with literature data of ΔGact. The parameter A implies a constant interfacial tension σsl=51 cal mol-1 cm-2 between the growing NAD germ and the supercooled solution. A slight temperature dependence of the diffusion activation energy is represented by the parameter B. Investigations with a detailed microphysical process model showed that literature formulations of volume-based (Salcedo et al., 2001) and surface-based (Tabazadeh et al., 2002) nucleation rates significantly overestimate NAD formation rates when applied to the conditions of our experiments.

EASTERN STAINLESS TYPE 310S

Alloy Digest ◽  
1984 ◽  
Vol 33 (8) ◽  
Keyword(s):  
High Temperatures ◽  
Elevated Temperatures ◽  
High Strength ◽  
Heat Treating ◽  
Oil Refining ◽  
Steel Company ◽  
Plant Equipment ◽  
The Many ◽  
Corrosion And Oxidation ◽  
Refining Equipment

Abstract EASTERN STAINLESS TYPE 310S has high resistance to corrosion and oxidation at high temperatures. It also has high strength at elevated temperatures. Thus it is especially suitable for service at high temperatures. It is very ductile and can be welded readily. Among the many applications for Type 310S, a few typical uses include annealing boxes, chemical plant equipment, fire box sheets, furnace linings, heat exchangers, oil-refining equipment, kiln linings and tube hangers. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as creep. It also includes information on high temperature performance and corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: SS-450. Producer or source: Eastern Stainless Steel Company.

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