scholarly journals Calculation of Diffusion Flows for the Formation of Phases in Alloys Iron-Carbon-Alloying Element

2019 ◽  
Vol 20 (2) ◽  
pp. 196-201
Author(s):  
S.V. Bobyr
Keyword(s):  
Phase Transformations ◽  
Nonequilibrium Thermodynamics ◽  
Thermodynamic System ◽  
Alloying Element ◽  
Two Phase ◽  
Method Of Calculation ◽  
Diffusion Flows

The method of calculation of diffusion flows under phase transformations in alloys iron - carbon - alloying element using the principles of nonequilibrium thermodynamics are developed. The expressions for calculation of cross-factors, motive forces and flows in the Onzager equations for a two-phase thermodynamic system, and an example of using the developed method are given.

Lithium electrochemical deintercalation from O2-LiCoO2: structural study and first principles calculations

2002 ◽  
Vol 756 ◽  
Author(s):  
D. Carlier ◽  
A. Van der Ven ◽  
G. Ceder ◽  
L. Croguennec ◽  
M. Ménétrier ◽  
...  
Keyword(s):  
Phase Transformations ◽  
Density Functional ◽  
Driving Forces ◽  
Charge Ordering ◽  
Ionic Exchange ◽  
Two Phase ◽  
Entropy Maximization ◽  
Vacancy Ordering ◽  
Voltage Curve ◽  
Ordered Phases

ABSTRACTWe present a detailed study of the O2-LiCoO2 phase used as positive electrode in lithium batteries. This phase is a metastable form of LiCoO2 and is prepared by ionic exchange from P2-Na0.70CoO2. The O2-LiCoO2 system presents interesting fundamental problems as it exhibits several phase transformations upon lithium deintercalation that imply either CoO2 sheet gliding or lithium/vacancy ordering. Two unusual structures are observed: T#2 and O6. The T#2 phase was characterized by X-ray, neutron and electron diffraction, whereas the O6 phase was only characterized by XRD.In order to better understand the structures and the driving forces responsible for the phase transformations involved in lithium deintercalation, we combine our experimental study of this system with a theoretical approach. The voltage-composition curve at room temperature is calculated using Density Functional Theory combined with Monte Carlo simulations, and is qualitatively in good agreement with the experimental voltage curve over the complete lithium composition range. Pseudopotential and thermodynamic calculations both show that two tetrahedral sites have to be considered for Li in the T#2 structure. The calculated voltage curve thus exhibits a two-phase O2/T#2 region that indicates that this phase transformation is driven by the entropy maximization and not by a non-metal to metal transition. We also predict two ordered phases for Li1/4CoO2 (O2) and Li1/3CoO2 (O6) and show that the formation of the O6 phase is not related to Li staging or Co3+/Co4+ charge ordering.

scholarly journals A Derivation of the Main Relations of Nonequilibrium Thermodynamics

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Vladimir N. Pokrovskii
Keyword(s):  
Nonequilibrium Thermodynamics ◽  
Second Law Of Thermodynamics ◽  
Thermodynamic System ◽  
Internal Variables ◽  
Second Law ◽  
Basic Principles ◽  
First Law Of Thermodynamics ◽  
Sum Of Products ◽  
Thermodynamic Forces ◽  
Production Of Entropy

The principles of nonequilibrium thermodynamics are discussed, using the concept of internal variables that describe deviations of a thermodynamic system from the equilibrium state. While considering the first law of thermodynamics, work of internal variables is taken into account. It is shown that the requirement that the thermodynamic system cannot fulfil any work via internal variables is equivalent to the conventional formulation of the second law of thermodynamics. These statements, in line with the axioms introducing internal variables can be considered as basic principles of nonequilibrium thermodynamics. While considering stationary nonequilibrium situations close to equilibrium, it is shown that known linear parities between thermodynamic forces and fluxes and also the production of entropy, as a sum of products of thermodynamic forces and fluxes, are consequences of fundamental principles of thermodynamics.

Phase Transformations during the Heating of Fe-Si-B Amorphous Alloys

2005 ◽  
Vol 237-240 ◽  
pp. 1205-1209
Author(s):  
O. Hryhoryeva ◽  
M. Belous ◽  
Sergey I. Sidorenko
Keyword(s):  
Magnetic Properties ◽  
Phase Transformations ◽  
Amorphous Alloys ◽  
Ray Method ◽  
X Ray ◽  
Method Of Calculation ◽  
Thermomagnetic Analysis ◽  
Magnetic Effects ◽  
Differential Technique

Phase transformations during the heating of amorphous Fe-Si-B alloys were investigated. The differential thermomagnetic analysis and X-ray method are used for the studies. The intervals of phase transformations are revealed, and the magnetic properties of phases are determined. The method of calculation of magnetic effects during the phase transformations, registered by differential technique is suggested.

scholarly journals Reply to “Comments on ‘MSE minus CAPE is the True Conserved Variable for an Adiabatically Lifted Parcel’”

2016 ◽  
Vol 73 (6) ◽  
pp. 2577-2583
Author(s):  
David M. Romps
Keyword(s):  
Triple Point ◽  
Specific Energy ◽  
Liquid Water ◽  
Thermodynamic System ◽  
Numerical Calculations ◽  
Two Phase ◽  
Point Temperature ◽  
Dry Air ◽  
Temperature And Pressure ◽  
Triple Point Temperature

Abstract A standard convention in moist thermodynamics, adopted by D. M. Romps and others, is to set the specific energy and entropy of dry air and liquid water to zero at the triple-point temperature and pressure. P. Marquet claims that this convention leads to physically incorrect results. To support this claim, Marquet presents numerical calculations of a lifted parcel. It is shown here that the claim is false and that the numerical calculations of Marquet are in error. In the context of a simple two-phase thermodynamic system, an analysis is presented here of the freedoms one has to choose additive constants in the definitions of energy and entropy. Many other misconceptions are corrected as well.

Geothermal Reservoir Simulation Using Nonequilibrium Thermodynamics

1983 ◽  
Vol 23 (04) ◽  
pp. 613-622
Author(s):  
V.V. Nguyen ◽  
G.F. Pinder
Keyword(s):  
Porous Media ◽  
Finite Difference ◽  
Nonequilibrium Thermodynamics ◽  
Fluid Pressure ◽  
Water System ◽  
Alternative View ◽  
Phase System ◽  
Two Phase ◽  
Preliminary Results ◽  
Geothermal Reservoirs

Abstract A phenomenological interpretation of the evolution of a steam/water system is proposed from a nonequilibrium mixture perspective. This type of thermodynamic behavior is structurally stable on the basis of catastrophe theory and therefore offers an unorthodox alternative approach to the simulation of geothermal reservoirs. Use of this approach in a one-dimensional (ID) finite-difference simulator yields results that can be compared with a traditional numerical scheme. Introduction All numerical simulators of geothermal reservoirs depend on an accurate representation of the thermodynamics of the steam/water system. This information is required to render tractable the system of balance equations derived from the physics of flow through porous media. While it is generally recognized that the porous media. While it is generally recognized that the two-phase system is not in thermodynamic equilibrium, equilibrium thermodynamics is universally employed in its description for numerical simulators (see Ref. 1 for a state-of-the-art review of these models). In this paper, we present an alternative view on nonequilibrium thermodynamics. A phenomenological investigation of the proposed approach has been reported by Nguyen at From this new perspective, we constrict a computational scheme that eliminates the difficulties often encountered in the two-phase region. Preliminary results of this work were reported by Preliminary results of this work were reported by Nguyen and Pinder. This study provides a description of a ID mathematical model of two-phase hydrothermal flow, an outline of the finite-difference procedure employed to approximate its solution. and a concise summary of the proposed nonequilibrium thermodynamics theory for the proposed nonequilibrium thermodynamics theory for the steam/water system. Also included are the computation scheme for the phase-transition problem and a numerical simulation that uses the experimental conditions given by Arihara et al. Governing Equations The equations describing unsteady I D flow in a horizontal two-phase hydrothermal system have been developed by several authors, and the derivation methods are not repeated here. These equations have the following forms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (1) and . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (2) where p is fluid pressure and h is enthalpy of the fluid mixture., and are nonlinear coefficients defined as follows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (3) SPEJ p. 613

ASSESSMENT OF THE INFLUENCE OF THE THERMODYNAMIC FACTOR ON THE CRYSTALLIZATION PROCESS IN A VACUUM APPARATUS

2021 ◽  
Author(s):  
Е.В. СЕМЕНОВ ◽  
А.А. СЛАВЯНСКИЙ ◽  
В.А. ГРИБКОВА ◽  
Д.П. МИТРОШИНА ◽  
Н.Н. ЛЕБЕДЕВА
Keyword(s):  
Phase Transformations ◽  
Crystallization Process ◽  
Physical Factor ◽  
Supersaturated Solution ◽  
Crystal Formation ◽  
Two Phase ◽  
Software Products ◽  
Diffusive Mass Transfer ◽  
Vacuum Apparatus ◽  
Technology Of Production

Особенность состояния системы жидкость–твердое тело в метастабильном растворе вещества состоит в том, что она (система) претерпевает два фазовых превращения в вакуум-аппарате (ВА) – кристаллообразование и растворение, требующие экспериментального изучения и описания в силу их важности при совершенствовании технологии производства кристаллического сахара. Однако и теоретическое обоснование фазовых превращений в метастабильном растворе разработано недостаточно. В статье предпринята попытка количественно поставить и решить проблему учета возникающего при проведении обработки метастабильного сахарсодержащего раствора повышения температуры в результате конденсации молекул на центре концентрации при пересыщении в ВА. В качестве основы численного моделирования поставленной задачи использовали программные продукты информационной среды Mathcad. С использованием модели диффузионного массопереноса сахарозы в пересыщенном растворе к затравке был разработан алгоритм расчета зависимости массы сахарозы от времени проведения процесса кристаллизации. На примере сахарозы дана оценка влияния физического фактора – выделяющейся при кристаллообразовании теплоты на расчет теплового баланса и производительности ВА. The peculiarity of the state of the liquid-solid system in a metastable solution of a substance is that it (the system) undergoes two phase transformations in a vacuum apparatus (VA) – crystal formation and dissolution, requiring experimental study and description due to their importance in improving the technology of production of crystalline sugar. However the theoretical justification of phase transformations in a metastable solution has not been sufficiently developed. The article attempts to quantify and solve the problem of taking into account the temperature increase that occurs during the processing of a metastable sugar-containing solution as a result of condensation of molecules at the concentration center during supersaturation in VA. Software products of the Mathcad information environment were used as the basis for numerical modeling of the task. Using a model of diffusive mass transfer of sucrose in a supersaturated solution to the seed, an algorithm was developed for calculating the dependence of the sucrose mass on the time of the crystallization process. On the example of sucrose, an assessment of the influence of a physical factor – the heat released during crystallization on the calculation of the thermal balance and the productivity of the VA is given.

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