scholarly journals Modeling of Thermal Conductivity in a Medium with Phase Transition with a Moving Boundary of Phase Change

2021 ◽  
pp. 53-61
Author(s):  
Vadim Mizonov ◽  
◽  
Andrei Tikhonov ◽  
Elena Basova ◽  
Andrei Mitrofanov ◽  
...  
Keyword(s):  
Phase Transition ◽  
Thermal Conductivity ◽  
Heat Treatment ◽  
Mathematical Model ◽  
Numerical Experiments ◽  
Moving Boundary ◽  
Phase Interface ◽  
Significant Feature ◽  
Engineering Practice ◽  
Interface Motion

This work is devoted to the theoretical study of the effect of the phase interface motion on thermal conductivity in a liquid-solid nonlinear medium with a phase transition. The problem under consideration deals with the Stefan problems. Its most significant feature is the jump in the phase properties at separation of their moving boundaries. The objective was achieved by solving the following tasks: the construction of the process mathematical model based on its cell representation and with the use of the Markov chain theory mathematical apparatus, performing numerical experiments with the developed model, demonstrating its operability and the possibility to achieve the set goal. The most significant scientific results were as follows. First was an algorithm for the construction of a cell mathematical model of nonlinear thermal conductivity in a phase transitions medium with a moving phase interface for domains of a canonical shape (plane wall, cylinder, ball). Second, the results of the numerical experiments, showing that the jump of properties affected greatly the kinetics of the process. The significance of the results obtained consisted in the development of a simple but informative mathematical model of the media heat treatment kinetics with phase transformations, available for a direct use in the engineering practice. The proposed algorithm for constructing the model can be effectively used in prediction the open water pipes freezing in cold regions, in modeling the heat treatment of metals, in choosing the freezing modes of food products for a long-term storage, and other thermo-physical processes.

Conduction Characteristics of Frosting Circumferential Fin of Rectangular Profile

2011 ◽  
Vol 354-355 ◽  
pp. 779-783
Author(s):  
Kun Feng Sun ◽  
Xiao Lu Wang ◽  
Heng Liang Zhang
Keyword(s):  
Thermal Conductivity ◽  
Mathematical Model ◽  
Analytical Solution ◽  
High Thermal Conductivity ◽  
Engineering Practice ◽  
Low Thermal Conductivity ◽  
Rectangular Profile ◽  
Alternative Approaches ◽  
Frost Layer ◽  
Form Of Expression

Through the appropriate assumptions, a mathematical model was derived on circumferential fin of rectangular profile coated with frost layer, and a new analytical solution is presented and compared to alternative approaches for calculating the fin temperature and efficiency. The analytical solution enhances the accuracy ,and have a simpler form of expression. It can be easily used in engineering practice. The solution is useful for other cases of a low-thermal-conductivity coating on a high-thermal-conductivity substrate .

scholarly journals ABOUT ONE APPROACH TO CALCULATION OF PARAMETERS OF HEAT TRANSFER THROUGH WALL IN PRESENCE OF CONDENSING VAPOR

2018 ◽  
Vol 61 (8) ◽  
pp. 89
Author(s):  
Aleksandr I. Moshinskiy ◽  
Pavel G. Ganin ◽  
Alla V. Markova ◽  
Larisa N. Rubtsova ◽  
Vladislav V. Sorokin
Keyword(s):  
Heat Transfer ◽  
Phase Transition ◽  
Mathematical Model ◽  
Heat Exchanger ◽  
Initial Approximation ◽  
Educational Process ◽  
Heat Transfer Agent ◽  
Engineering Practice ◽  
Stationary Mode ◽  
The Mathematical Model

The article is dedicated to the study of heat exchangers operation. The main goal of the work was to improve a standard method for calculating a typical heat exchanger based on dependencies approved in engineering practice. The noted technique is presented in educational literature for chemical engineers and it is included in the educational process for the training of engineers. On the basis of practical recommendations stated in literature the working formulas of the process are taken in approximate form. Further, a correction is calculated, which, as calculations show, leads (together with the initial approximation) to an almost exact satisfaction of the initial equations. It is expedient because traditional equations of a heat transfer have not really high precision, which is determined by the processing of numerous experiments. These experiments are rather rough. It is reasonable that the accuracy of the analysis has to be consistent with the model accuracy. This factor justifies the need to simplify the models (use of various recommendations based on the experience of equipment operation, etc.). At the same time, it is desirable to simplify the mathematical model equation so that it is possible to calculate the corrections, i.e. to clarify the solution. We clarify the equation solution meaning more and more exact satisfaction with the initial equation of the mathematical model. In this direction, various variants of perturbation methods can be used. The search for analytical solutions is complicated by the fact that the equations of the mathematical model of energy transfer in a heat exchanger are nonlinear. The three-layer heat transfer problem in a stationary mode is considered.  The first layer is the space of the heat exchanger where a phase transition (first heat transfer agent vapor condensation) occurs. The second layer is the space of the heat exchanger where convective movement of the second heat transfer agent takes place without phase transition. The third layer is a wall separating the heat transfer agent providing some resistance to the heat transfer process. As a result of the simplified model analysis, it became possible to obtain an analytical solution to the problem with such accuracy that the calculated correction turned out to be insignificant i.e. the correction is not appropriate to take into account. The solution found was almost exactly approximated by a simple analytic dependence.

CMW 100

Alloy Digest ◽  
2000 ◽  
Vol 49 (10) ◽  
Keyword(s):  
Thermal Conductivity ◽  
Heat Treatment ◽  
Copper Alloy ◽  
High Strength ◽  
Heat Treating ◽  
Age Hardening ◽  
High Tensile Strength ◽  
Electrical Components ◽  
Flash Welding ◽  
Hardening Heat Treatment

Abstract CMW 100 is a copper alloy that combines high tensile strength with high electrical and thermal conductivity. It responds to age-hardening heat treatment. It is used for flash welding dies, springs, electrical components, high-strength backing material for brazed assemblies, and wire guides. This datasheet provides information on composition, physical properties, hardness, and tensile properties as well as fatigue. It also includes information on corrosion resistance as well as forming, heat treating, machining, joining, and surface treatment. Filing Code: CU-29. Producer or source: CMW Inc. Originally published as Mallory 100, August 1955, revised October 2000.

scholarly journals Computer Modeling of Aerosol Emissions Spread in the Atmosphere

2019 ◽  
Vol 97 ◽  
pp. 05023 ◽  
Author(s):  
Daler Sharipov ◽  
Sharofiddin Aynakulov ◽  
Otabek Khafizov
Keyword(s):  
Boundary Layer ◽  
Mathematical Model ◽  
Atmospheric Boundary Layer ◽  
Computer Modeling ◽  
Numerical Experiments ◽  
Climatic Factors ◽  
Numerical Algorithms ◽  
Aerosol Emissions ◽  
The Given ◽  
And Diffusion

The paper deals with the development of mathematical model and numerical algorithms for solving the problem of transfer and diffusion of aerosol emissions in the atmospheric boundary layer. The model takes into account several significant parameters such as terrain relief, characteristics of underlying surface and weather-climatic factors. A series of numerical experiments were conducted based on the given model. The obtained results presented here show how these factors affect aerosol emissions spread in the atmosphere.

scholarly journals The origin of the lattice thermal conductivity enhancement at the ferroelectric phase transition in GeTe

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Đorđe Dangić ◽  
Olle Hellman ◽  
Stephen Fahy ◽  
Ivana Savić
Keyword(s):  
Phase Transition ◽  
Thermal Conductivity ◽  
Phase Transitions ◽  
Thermoelectric Materials ◽  
Ferroelectric Phase Transition ◽  
Lattice Thermal Conductivity ◽  
Ferroelectric Phase ◽  
Structural Phase ◽  
High Symmetry ◽  
Structural Phase Transitions

AbstractThe proximity to structural phase transitions in IV-VI thermoelectric materials is one of the main reasons for their large phonon anharmonicity and intrinsically low lattice thermal conductivity κ. However, the κ of GeTe increases at the ferroelectric phase transition near 700 K. Using first-principles calculations with the temperature dependent effective potential method, we show that this rise in κ is the consequence of negative thermal expansion in the rhombohedral phase and increase in the phonon lifetimes in the high-symmetry phase. Strong anharmonicity near the phase transition induces non-Lorentzian shapes of the phonon power spectra. To account for these effects, we implement a method of calculating κ based on the Green-Kubo approach and find that the Boltzmann transport equation underestimates κ near the phase transition. Our findings elucidate the influence of structural phase transitions on κ and provide guidance for design of better thermoelectric materials.

scholarly journals A Molecular Model of PEMFC Catalyst Layer: Simulation on Reactant Transport and Thermal Conduction

Membranes ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 148
Author(s):  
Wenkai Wang ◽  
Zhiguo Qu ◽  
Xueliang Wang ◽  
Jianfei Zhang
Keyword(s):  
Thermal Conductivity ◽  
Proton Exchange Membrane ◽  
Molecular Model ◽  
Phase Interface ◽  
Catalyst Layer ◽  
Md Simulations ◽  
Distribution Functions ◽  
Proton Exchange ◽  
Pt Catalyst ◽  
Reaction Efficiency

Minimizing platinum (Pt) loading while reserving high reaction efficiency in the catalyst layer (CL) has been confirmed as one of the key issues in improving the performance and application of proton exchange membrane fuel cells (PEMFCs). To enhance the reaction efficiency of Pt catalyst in CL, the interfacial interactions in the three-phase interface, i.e., carbon, Pt, and ionomer should be first clarified. In this study, a molecular model containing carbon, Pt, and ionomer compositions is built and the radial distribution functions (RDFs), diffusion coefficient, water cluster morphology, and thermal conductivity are investigated after the equilibrium molecular dynamics (MD) and nonequilibrium MD simulations. The results indicate that increasing water content improves water aggregation and cluster interconnection, both of which benefit the transport of oxygen and proton in the CL. The growing amount of ionomer promotes proton transport but generates additional resistance to oxygen. Both the increase of water and ionomer improve the thermal conductivity of the C. The above-mentioned findings are expected to help design catalyst layers with optimized Pt content and enhanced reaction efficiency, and further improve the performance of PEMFCs.

A mathematical model for heterogeneous reactions with a moving boundary

AIChE Journal ◽  
1989 ◽  
Vol 35 (4) ◽  
pp. 625-634 ◽  
Author(s):  
Kareem I. Batarseh ◽  
Glenn P. Swaney ◽  
Alfred H. Stiller
Keyword(s):  
Mathematical Model ◽  
Moving Boundary ◽  
Heterogeneous Reactions

Rem and Rheed Studies of Pb Adsorption on Si(111)

1992 ◽  
Vol 280 ◽  
Author(s):  
Yasumasa Tanishiro ◽  
Masahiko Fukuyamaand ◽  
Katsumichi Yagi
Keyword(s):  
Phase Transition ◽  
Heat Treatment ◽  
Phase Diagram ◽  
Surface Structures ◽  
Structure Changes ◽  
Incommensurate Structures

ABSTRACTStructure changes of Si(111)-Pb surfaces due to deposition and heat treatment are studied by REM-RHEED. Surface structures observed are summarized as a phase diagram. Formation of an incommensurate layer(α) and a phase transition between incommensurate structures of α and α' is described.

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