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Wyświetlanie 1-15 z 33
Tytuł:
Rayleigh-Bénard convection in an elastico-viscous Walters’ (model B’) nanofluid layer
Autorzy:
Rana, G. C.
Chand, R.
Powiązania:
https://bibliotekanauki.pl/articles/202036.pdf
Data publikacji:
2015
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
nanofluid
oscillatory convection
Rayleigh-Benard convection
viscoelasticity
Walters' (model B') fluid
oscylacyjna konwekcyjna
komórki Bénarda
lepkosprężystość
Opis:
In this study, the onset of convection in an elastico-viscous Walters’ (model B’) nanofluid horizontal layer heated from below is considered. The Walters’ (model B’) fluid model is employed to describe the rheological behavior of the nanofluid. By applying the linear stability theory and a normal mode analysis method, the dispersion relation has been derived. For the case of stationary convection, it is observed that the Walters’ (model B’) elastico-viscous nanofluid behaves like an ordinary Newtonian nanofluid. The effects of the various physical parameters of the system, namely, the concentration Rayleigh number, Prandtl number, capacity ratio, Lewis number and kinematics visco-elasticity coefficient on the stability of the system has been numerically investigated. In addition, sufficient conditions for the non-existence of oscillatory convection are also derived.
Źródło:
Bulletin of the Polish Academy of Sciences. Technical Sciences; 2015, 63, 1; 235-244
0239-7528
Pojawia się w:
Bulletin of the Polish Academy of Sciences. Technical Sciences
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The modified XFEM for solving problems of a phase change with natural convection
Autorzy:
Stąpór, Paweł
Powiązania:
https://bibliotekanauki.pl/articles/139838.pdf
Data publikacji:
2019
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
phase change
natural convection
extended finite element method
level set method
Opis:
This paper presents an extended finite element method applied to solve phase change problems taking into account natural convection in the liquid phase. It is assumed that the transition from one state to another, e.g., during the solidification of pure metals, is discontinuous and that the physical properties of the phases vary across the interface. According to the classical Stefan condition, the location, topology and rate of the interface changes are determined by the jump in the heat flux. The incompressible Navier–Stokes equations with the Boussinesq approximation of the natural convection flow are solved for the liquid phase. The no-slip condition for velocity and the melting/freezing condition for temperature are imposed on the interface using penalty method. The fractional four-step method is employed for analysing conjugate heat transfer and unsteady viscous flow. The phase interface is tracked by the level set method defined on the same finite element mesh. A new combination of extended basis functions is proposed to approximate the discontinuity in the derivative of the temperature, velocity and the pressure fields. The single-mesh approach is demonstrated using three two-dimensional benchmark problems. The results are compared with the numerical and experimental data obtained by other authors.
Źródło:
Archive of Mechanical Engineering; 2019, LXVI, 3; 273-294
0004-0738
Pojawia się w:
Archive of Mechanical Engineering
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A Mechanistic Model of a Passive Autocatalytic Hydrogen Recombiner
Autorzy:
Rożeń, A.
Powiązania:
https://bibliotekanauki.pl/articles/184900.pdf
Data publikacji:
2015
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
hydrogen
catalysis
laminar flow
natural convection
forced convection
wodór
kataliza
przepływ laminarny
konwekcja naturalna
konwekcja wymuszona
Opis:
A passive autocatalytic hydrogen recombiner (PAR) is a self-starting device, without operator action or external power input, installed in nuclear power plants to remove hydrogen from the containment building of a nuclear reactor. A new mechanistic model of PAR has been presented and validated by experimental data and results of Computational Fluid Dynamics (CFD) simulations. The model allows to quickly and accurately predict gas temperature and composition, catalyst temperature and hydrogen recombination rate. It is assumed in the model that an exothermic recombination reaction of hydrogen and oxygen proceeds at the catalyst surface only, while processes of heat and mass transport occur by assisted natural and forced convection in non-isothermal and laminar gas flow conditions in vertical channels between catalyst plates. The model accounts for heat radiation from a hot catalyst surface and has no adjustable parameters. It can be combined with an equation of chimney draft and become a useful engineering tool for selection and optimisation of catalytic recombiner geometry.
Źródło:
Chemical and Process Engineering; 2015, 36, 1; 3-19
0208-6425
2300-1925
Pojawia się w:
Chemical and Process Engineering
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The onset of thermal convection in couple-stress fluid in hydromagnetics saturating a porous medium
Autorzy:
Rana, G. C.
Powiązania:
https://bibliotekanauki.pl/articles/201216.pdf
Data publikacji:
2014
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
couple stress fluid
magnetic field
porous medium
thermal convection
Opis:
In this paper, the effect of magnetic field on thermal convection in couple-stress fluid saturating a porous medium is considered. By applying linear stability theory and the normal mode analysis method, a mathematical theorem is derived which states that the viscoelastic thermal convection at marginal state, cannot manifest as stationary convection if the thermal Rayleigh number R, the medium permeability parameter Pι the couple-stress parameter F and the Chandrasekher number Q, satisfy the inequality R ≤4π2/Pl (1 + 2π2F + PlQ/2ε) the result clearly establishes the stabilizing character of couple-stress parameter and magnetic field whereas destabilizing character of medium permeability.
Źródło:
Bulletin of the Polish Academy of Sciences. Technical Sciences; 2014, 62, 2; 357-362
0239-7528
Pojawia się w:
Bulletin of the Polish Academy of Sciences. Technical Sciences
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Intensification of free-convection heat transfer in magnetically assisted bioreactor
Autorzy:
Konopacki, Maciej
Kordas, Marian
Rakoczy, Rafał
Powiązania:
https://bibliotekanauki.pl/articles/185473.pdf
Data publikacji:
2019
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
natural convection
rotating magnetic field
magnetically assisted bioreactor
Naturalna konwekcja
wirujące pole magnetyczne
bioreaktor wspomagany magnetycznie
Opis:
The effect of rotating magnetic field on the heat transfer process in a magnetically assisted bioreactor was studied experimentally. Experimental investigations are provided for the explanation of the influence of the rotating magnetic field on natural convection. The heat transfer coefficients and the Nusselt numbers were determined as a function of the product of Grashof and Prandtl dimensionless numbers. Moreover, the comparison of the thermal performance between the tested set-up and a vertical cylinder was carried out. The relative enhancement of heat transfer was characterized by the rate of the relative heat transfer intensification. The study showed that along with the intensity of the magnetic field the heat transfer increased.
Źródło:
Chemical and Process Engineering; 2019, 40, 3; 293--304
0208-6425
2300-1925
Pojawia się w:
Chemical and Process Engineering
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Inverse Solution to the Vertical Plate Cooling by Radiation and Convection in Air
Autorzy:
Hadała, Beata
Malinowski, Zbigniew
Gołdasz, Andrzej
Cebo-Rudnicka, Agnieszka
Powiązania:
https://bibliotekanauki.pl/articles/2134090.pdf
Data publikacji:
2022
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
convection heat transfer
radiation heat transfer
plate emissivity
vertical plate
Opis:
The inverse solution to the heat flux identification during the vertical plate cooling in air has been presented. The developed solution allowed to separate the energy absorbed by the chamber due to radiation from the convection heat losses to air. The uncertainty tests were carried out and the accuracy of the solution has been estimated at a level of 1%-5% depending on the boundary condition model. The inverse solution was obtained for the temperature measurements in the vertical plate. The stainless-steel plate was heated to 950°C and then cooled in the chamber in air only to about 30°C. The identified heat transfer coefficient was compared with the Churchill and Chu model. The solution has allowed to separate the radiation heat losses and to determine the Nusselt number values that stay in good agreement with the Churchill and Chu model for a nearly steady-state air flow for the plate temperature below 100°C.
Źródło:
Archives of Metallurgy and Materials; 2022, 67, 3; 1167--1178
1733-3490
Pojawia się w:
Archives of Metallurgy and Materials
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Analysis of components effecting free convection intensity in steel rectangular sections
Autorzy:
Wyczółkowski, R.
Powiązania:
https://bibliotekanauki.pl/articles/240388.pdf
Data publikacji:
2015
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
free convection
Rayleigh number
section bundles
effective thermal conductivity
heat treatment
konwekcja swobodna
liczbia Rayleigha
efektywna przewodność cieplna
obróbka cieplna
Opis:
Free convection is one of the heat transfer modes which occurs within the heat-treated bundles of steel rectangular section. A comprehensive study of this phenomenon is necessary for optimizing the heating process of this type of charge. The free convection intensity is represented by the Rayleigh number Ra. The value of this criterion depends on the following parameters: the mean section temperature, temperature difference within the section, kinematic coefficient of viscosity, volume expansion coefficient and the Prandtl number. The paper presents the analysis of the impact of these factors on free convection in steel rectangular sections. The starting point for this analysis were the results of experimental examinations. It was found that the highest intensity of this process occurs for the temperature of 100°C. This is mainly caused by changes in the temperature difference observed in the area of sections and changes in kinematic coefficient of viscosity of air. The increase in the value of the Rayleigh number criterion at the initial stage is attributable to changes in the parameter of temperature difference within the section. After exceeding 100°C, the main effect on convection is from changes in air viscosity. Thus, with further increase in temperature, the Rayleigh number starts to decline rapidly despite further rise in the difference in temperature.
Źródło:
Archives of Thermodynamics; 2015, 36, 3; 105-121
1231-0956
2083-6023
Pojawia się w:
Archives of Thermodynamics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Analysis of the occurrence of natural convection in a bed of bars in vertical temperature gradient conditions
Autorzy:
Wyczółkowski, R.
Musiał, D.
Powiązania:
https://bibliotekanauki.pl/articles/239971.pdf
Data publikacji:
2013
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
natural convection
bed of bars
porous material
konwekcja naturalna
złoża prętów
materiały porowate
Opis:
The reason for undertaking this study was to determine the possible involvement of natural convection in the global heat transfer, that occurs in the heated steel rods bed. This problem is related to the setting of the effective thermal conductivity of the bars bed. This value is one of the boundary conditions for heating modeling of steel rods bundles during heat treatment. The aim of this study was to determine for which geometry of the bed bars, there will be no free convection. To analyze the problem the Rayleigh criterion was used. It was assumed that for the value of the number Ra < 1700 convection in the bed bars does not occur. For analysis, the results of measurements of the temperature distribution in the unidirectionally heated beds of bars were used. It has been shown, that for obtained, during the test, differences of temperature between the surfaces of adjacent rods, convection can occur only when the diameter of the rod exceeds 18 mm.
Źródło:
Archives of Thermodynamics; 2013, 34, 1; 71-83
1231-0956
2083-6023
Pojawia się w:
Archives of Thermodynamics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Boundary effects on electrothermal convection in a dielectric fluid layer
Autorzy:
Ravisha, M.
Raghunatha, K. R.
Mamatha, A. L.
Shivakumara, I. S.
Powiązania:
https://bibliotekanauki.pl/articles/240648.pdf
Data publikacji:
2019
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
boundary effect
dielectric fluid
AC electric field
thermal convection
konwekcja termiczna
płyn dielektryczny
warunki brzegowe
Opis:
The instability characteristics of a dielectric fluid layer heated from below under the influence of a uniform vertical alternating current (AC) electric field is analyzed for different types of electric potential (constant electric potential/ electric current), velocity (rigid/free) and temperature boundary conditions (constant temperature/heat flux or a mixed condition at the upper boundary). The resulting eigenvalue problem is solved numerically using the shooting method for various boundary conditions and the solution is also found in a simple closed form when the perturbation heat flux is zero at the boundaries. The possibility of a more precise control of electrothermal convection (ETC) through various boundary conditions is emphasized. The effect of increasing AC electric Rayleigh number is to hasten while that of Biot number is to delay the onset of ETC. The system is more stable for rigid-rigid boundaries when compared to rigid-free and least stable for free-free boundaries. The change of electric potential boundary condition at the upper boundary from constant electric potential to constant electric current is found to instill more stability on the system.
Źródło:
Archives of Thermodynamics; 2019, 40, 1; 3-19
1231-0956
2083-6023
Pojawia się w:
Archives of Thermodynamics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Natural convection heat transfer in heated vertical tubes with internal rings
Autorzy:
Nayak, R. C.
Roul, M. K.
Sarangi, S. K.
Powiązania:
https://bibliotekanauki.pl/articles/240303.pdf
Data publikacji:
2018
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
heat flux
heat transfer
natural convection
ring spacing
ring thickness
strumień cieplny
wymiana ciepła
konwekcja naturalna
pierścień
Opis:
Experimental investigation of natural convection heat transfer in heated vertical tubes dissipating heat from the internal surface is presented. The test section is electrically heated and constant wall heat flux is maintained both circumferentially and axially. Four different test sections are taken having 45 mm internal diameter and 3.8 mm thickness. The length of the test sections are 450 mm, 550 mm, 700 mm and 850 mm. Ratios of length to diameter of the test sections are taken as 10, 12.22, 15.56, and 18.89. Wall heat fluxes are maintained at 250–3341 W/m2 . Experiments are also conducted on channels with internal rings of rectangular section placed at various distances. Thickness of the rings are taken as 4 mm, 6 mm, and 8 mm. The step size of the rings varies from 75 mm to 283.3 mm. The nondimensional ring spacing, expressed as the ratios of step size to diameter, are taken from 1.67 to 6.29 and the non-dimensional ring thickness, expressed as the ratios of ring thickness to diameter are taken from 0.089 to 0.178. The ratios of ring spacing to its thickness are taken as 9.375 to 70.82. The effects of various parameters such as length to diameter ratio, wall heat flux, ring thickness and ring spacing on local steady-state heat transfer behavior are observed. From the experimental data a correlation is developed for average Nusselt number and modified Rayleigh number. Another correlation is also developed for modified Rayleigh number and modified Reynolds number. These correlations can predict the data accurately within ±10% error.
Źródło:
Archives of Thermodynamics; 2018, 39, 4; 85--111
1231-0956
2083-6023
Pojawia się w:
Archives of Thermodynamics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Analysis of thermal stratified storage tank
Autorzy:
Smusz, R.
Kielan, P.
Mazur, D.
Powiązania:
https://bibliotekanauki.pl/articles/140948.pdf
Data publikacji:
2017
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
temperature stratification
thermal energy
heat recovery
convection
Opis:
The basic aim of the task is to compile a temperature stratification system in an accumulation tank. The range of the thesis concerns the shape and dimensions of a stratification system for an accumulation tank. Thermal stratification is a process that comprises the maintaining of temperature stratification at different levels of an accumulation tank which reduce to a minimum the process of temperature equalization. It results from the fact that the thermal stratification in a tank significantly increases the installation efficiency and improves the process of energy storing. It is connected with a thermodynamic element quality, that is the higher the temperature, the higher the energy, and, thus, the thermosdynamic element quality. In this phenomenon, thanks to the same amount of accumulated thermal energy and average temperature, as in a fully mixed tank, the user has a higher temperature in the upper part of the tank at his disposal. It has significant importance in the case when there is a low-temperature heating medium that transfers heat to the accumulation tank. Such a situation occurs when heat is absorbed from synthetic freons used in cooling and air-conditioning systems.
Źródło:
Archives of Electrical Engineering; 2017, 66, 3; 631-642
1427-4221
2300-2506
Pojawia się w:
Archives of Electrical Engineering
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Numerical study on the effects of multiple internal diathermal obstructions on natural convection in a fluid-saturated porous enclosure
Autorzy:
Chordiya, J. S.
Sharma, R. V.
Powiązania:
https://bibliotekanauki.pl/articles/139520.pdf
Data publikacji:
2018
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
thermal insulation
natural convection
internal obstructions
porous enclosure
Darcy's law
izolacja termiczna
konwekcja naturalna
przeszkody wewnętrzne
obudowa porowata
prawo Darcy'ego
Opis:
The present work aims at studying the effects of orientation, size, position, and the combination of multiple internal diathermal obstructions in a fluid-saturated square porous enclosure, generally encountered in thermal insulations. The overall objective is to suppress the natural convection fluid flow and heat transfer across a differentially heated porous enclosure. To serve this purpose, multiple diathermal obstructions are employed to mechanically protrude into a porous medium. It is sought to estimate the effect of various types of orientation, clustering and alternate positioning of obstructions by considering number of obstructions (Np), length of obstructions (λ), modified Rayleigh number (Ra*) on local and average Nusselt number (Nu). The Darcy model for porous media is solved using Finite difference method along with Successive Accelerated Replacement scheme. One of the findings is that the value of the Nusselt number decreases by increasing both, the number of obstructions as well as the length of obstructions irrespective of its orientation and positioning. The reduction in Nusselt number is significant with obstructions attached on lower half of the hot wall and/or on upper half of cold wall. In addition, the overall reduction in Nusselt number is slightly greater with obstructions attached explicitly to the cold wall.
Źródło:
Archive of Mechanical Engineering; 2018, LXV, 4; 553-578
0004-0738
Pojawia się w:
Archive of Mechanical Engineering
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Effects of variable viscosity on natural convection flow of an optically thick gray gas past a horizontal surface in the presence of internal heat generation
Autorzy:
Kannan, T.
Malleswaran, A.
Moorthy, M. B. K.
Powiązania:
https://bibliotekanauki.pl/articles/175425.pdf
Data publikacji:
2018
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
assisting and opposing flows
Dufour and Soret effects
internal heat generation
natural convection
radiation
variable viscosity
Opis:
A numerical investigation to discuss the effects of radiation and variable viscosity on heat and mass transfer characteristics of natural convection over a horizontal surface embedded in a saturated porous medium in the presence of internal heat generation is carried out in this study. The working fluid for the investigation is optically thick gray gas. The Dufour and Soret effects are also taken into account. Similarity transformations are employed to obtain nonlinear ordinary differential equations from the governing equations of the present problem. The numerical results for the transformed governing equations are computed by using commercial boundary value problem solver for ordinary differential equations. The effects are discussed by varying the parameters such as radiation, Dufour and Soret numbers, buoyancy ratio, Prandtl number, Schmidt number, and variable viscosity. Presence of internal heat generation enhances the velocity profile and significantly decreases the concentration boundary layer thickness. On increasing fluid radiation, the temperature of the fluid is higher than that of the surface and the concentration boundary layer thickness decreases away from the surface.
Źródło:
Transactions of the Institute of Fluid-Flow Machinery; 2018, 139; 3-22
0079-3205
Pojawia się w:
Transactions of the Institute of Fluid-Flow Machinery
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Effect of aspect ratio of enclosure on free convection from horizontal cylinders in Bingham plastic fluids
Autorzy:
Baranwal, Ashok Kumar
Gupta, Anoop Kumar
Tiwari, Anurag Kumar
Melnik, Roderick
Powiązania:
https://bibliotekanauki.pl/articles/2173430.pdf
Data publikacji:
2022
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
Bingham plastic fluids
aspect ratio
Rayleigh number
Nusselt number
natural convection
płyn plastikowy Bingham
współczynnik proporcji
liczba Rayleigha
liczba Nusselta
naturalna konwekcja
Opis:
Heat transfer in steady free convection from differentially heated cylinders enclosed in a rectangular duct filled with Bingham plastic fluids has been solved numerically for the ranges of the dimensionless groups as, Rayleigh number, 102 Ra 106; Prandtl number, 10 Pr 100 and, Bingham number, 0 Bn 50 for aspect ratios AR = 05, 0.6, 0.7, 0.8, 0.9 and 2. The streamlines, isotherm contours, yield surfaces, local and average Nusselt numbers were analysed and discussed. It is found that as the aspect ratio of the enclosure increases from 0.5 to 0.9, the average Nusselt number on the surface of the hot cylinder increases as a larger amount of fluid takes part in convection. Moreover, at sufficiently large Bingham numbers, yield stress forces dominate over buoyancy causing the flow to cease and thus the Nusselt number approaches its conduction limit. Finally, the Nusselt number approaches its conduction limit once the maximum Bingham number is reached.
Źródło:
Chemical and Process Engineering; 2022, 43, 2; 271--277
0208-6425
2300-1925
Pojawia się w:
Chemical and Process Engineering
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Effect Of Natural Convection On Directional Solidification Of Pure Metal
Wpływ konwekcji swobodnej na krzepnięcie kierunkowe czystego metalu
Autorzy:
Skrzypczak, T.
Węgrzyn-Skrzypczak, E.
Winczek, J.
Powiązania:
https://bibliotekanauki.pl/articles/356653.pdf
Data publikacji:
2015
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
pure metal
solidification
sharp interface
natural convection
Finite Element Method (FEM)
Level Set Method
czysty metal
krzepnięcie
ostry front
konwekcja naturalna
metoda elementów skończonych
metoda poziomic
Opis:
The paper is focused on the modeling of the directional solidification process of pure metal. During the process the solidification front is sharp in the shape of the surface separating liquid from solid in three dimensional space or a curve in 2D. The position and shape of the solid-liquid interface change according to time. The local velocity of the interface depends on the values of heat fluxes on the solid and liquid sides. Sharp interface solidification belongs to the phase transition problems which occur due to temperature changes, pressure, etc. Transition from one state to another is discontinuous from the mathematical point of view. Such process can be identified during water freezing, evaporation, melting and solidification of metals and alloys, etc. The influence of natural convection on the temperature distribution and the solid-liquid interface motion during solidification of pure copper is studied. The mathematical model of the process is based on the differential equations of heat transfer with convection, Navier-Stokes equation and the motion of the interface. This system of equations is supplemented by the appropriate initial and boundary conditions. In addition the continuity conditions at the solidification interface must be properly formulated. The solution involves the determination of the temporary temperature and velocity fields and the position of the interface. Typically, it is impossible to obtain the exact solution of such problem. The numerical model of solidification of pure copper in a closed cavity is presented, the influence of the natural convection on the phase change is investigated. Mathematical formulation of the problem is based on the Stefan problem with moving internal boundaries. The equations are spatially discretized with the use of fixed grid by means of the Finite Element Method (FEM). Front advancing technique uses the Level Set Method (LSM). Chorin’s projection method is used to solve Navier-Stokes equation. Such approach makes possible to uncouple velocities and pressure. The Petrov-Galerkin formulation is employed to stabilize numerical solutions of the equations. The results of numerical simulations in the 2D region are discussed and compared to the results obtained from the simulation where movement of the liquid phase was neglected.
Praca porusza problematykę modelowania kierunkowego krzepnięcia czystego metalu. Podczas tego procesu obserwuje się formowanie ostrego frontu krzepnięcia w postaci powierzchni separującej ciecz i ciało stałe w przypadku trójwymiarowym lub krzywej w przypadku płaskim. Położenie oraz kształt interfejsu krzepnięcia zmieniają się w czasie a wartości prędkości lokalnych zależą od różnicy intensywności strumieni ciepła po stronie ciała stałego i cieczy. Krzepnięcie z ostrym frontem należy do grupy procesów z przemianami fazowymi, które warunkowane są zmianami temperatury, ciśnienia, itp. Przejście fazowe z jednego stanu w drugi ma z matematycznego punktu widzenia charakter nieciągły. Procesy tego typu można zidentyfikować podczas zamarzania wody, parowania, topnienia i krzepnięcia metali i stopów, itp. W pracy zbadano wpływ zjawiska konwekcji swobodnej na chwilowy rozkład temperatury oraz ruch granicy narastania fazy stałej podczas krzepnięcia czystej miedzi w obszarze płaskim. Model matematyczny sformułowano na bazie równań różniczkowych transportu ciepła z konwekcją, Naviera-Stokesa i ruchu frontu krzepnięcia. Układ równań uzupełniono odpowiednimi warunkami początkowymi i brzegowymi oraz warunkami ciągłości na froncie. Rozwiązanie obejmuje chwilowe rozkłady temperatury, prędkości oraz położenie granicy międzyfazowej. Sformułowanie matematyczne zagadnienia bazuje na modelu z ruchomymi granicami wewnętrznymi, czyli tzw. modelu Stefana. Równania zostały zdyskretyzowane przestrzennie z wykorzystaniem metody elementów skończonych. W modelu numerycznym wykorzystano siatkę niezmienną w czasie. Do propagacji frontu użyto metody poziomic. Do wyznaczenia prędkości w cieczy wykorzystano metodę rzutowania, która poprzez eliminację ciśnienia z równania pędu pozwala na rozprzężenie prędkości i ciśnień. Równania rozwiązano z wykorzystaniem sformułowania Petrova-Galerkina. Omówiono wyniki analizy numerycznej oraz porównano je z wynikami otrzymanymi z symulacji, w której pominięto ruch cieczy.
Źródło:
Archives of Metallurgy and Materials; 2015, 60, 2A; 835-841
1733-3490
Pojawia się w:
Archives of Metallurgy and Materials
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 33

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