Wyniki wyszukiwania - Biblioteka Nauki

1

A mathematical theorem in double diffusive convection problem of viscoelastic fluid

100%

Mohan H. , Kumar P.

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2011

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tom Vol. 33, nr 4

49-61

EN

The present paper establishes mathematically that viscoelastic thermosolutal convection of Veronis type cannot manifest itself as oscillatory motion of growing amplitude in an initially bottom heavy configuration if the thermal Rayleigh number , the Lewis number , the Prandtl number and the viscoelastic parameter F satisfy the inequality. A similar mathematical theorem is also proved for Stern's type configuration.

2

Strumienie ciepła w rurach okrągłych w przypadku asymetrii współczynników wymiany ciepła

80%

Pelińska-Olko E. , Szarynger J.

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2006

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tom Vol. 11,spec.1/2

492-499

EN

The paper continues the subject matter, which is described in earlier works. It is connected with critical heat streams penetrating through the circular pipes and pipes with specific shapes (type R). We have made an assumption that the convective heat-transfer coefficient is constant on the circumference of the pipe. We show here the influence of the heat transfer conditions on outer surface (so called the pipe with outer asymmetry of the boundary conditions) on the heat stream penetrating through the circular pipe.

3

Effect of the magnetic field on forced convection flow along a wedge with variable viscosity

70%

Dimian M. F.

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2004

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tom Vol. 7, nr 1

107-117

EN

This paper presents a study of the flow of a viscous incompressible fluid along a heated wedge, taking into account the variation of the viscosity with temperature. The flow is under the influence of a magnetic field B(x) along y direction applied perpendicular to the surface of the boundary layer along x direction and an electric field E(x) along z direction. The boundary layer equations are transformed to nonlinear ordinary differential equations and are solved numerically. The effects of the magnetic field on the velocity and the temperature and the shear stress on the surface (Tw) are studied. It is found that the velocity of the fluid increases with increasing the magnetic field parameter M, with the other parameters kept constant. It is also established that the temperature of the wedge decreases with increasing M value. The value of the skin friction increases whereas the rate of heat transfer decreases owing to increasing the magnetic field parameter and also according to decreasing the viscosity.

4

Mixed convection flow of micropolar fluid in a vertical channel with symmetric and asymmetric wall heating conditions

70%

Umavathi J. C. , Prathap Kumar J.

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2011

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tom Vol. 16, no 1

141-159

EN

The theory of micro polar fluids due to Eringen is used to formulate a set of equations for the mixed convective flow and heat transfer in a vertical channel. The two boundaries of the channel are kept either at equal or at different temperatures. Through a proper choice of non-dimensional variables and parameters, the governing equations are developed and three types of thermal boundary conditions are prescribed. These thermal boundaries are isothermal-isothermal, isoflux-isothermal and isothermal-isoflux for the left-right walls of the channel. Exact analytical solutions are obtained for the velocity and temperature fields for heat generation/absorption conditions. It is found that the material and source/sink parameters have significant effects on the flow. A parametric study is conducted and the results are presented and discussed. By making the Newtonian solvent more and more micropolar, it is possible to obtain drag reduction.

5

Unsteady free convection flow in the stagnation-point region of a rotating sphere embedded in a porous medium

60%

Hassanien I. A. , Ibrahim F. S. , Omer G. M.

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2004

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tom Vol. 7, nr 2

89-98

EN

The problem of the unsteady free convection flow in a fluid saturated porous medium of a rotating sphere in the presence of a solid matrix exerting first and second resistance is studied. Numerical solutions are obtained for the cases of constant wall temperature (CWT) and constant heat flux (CHF). The non-linear coupled partial differential equations governing the flow have been solved numerically using finite difference. The effects of the first resistance parameter ξ, the buoyancy parameter λ, the Prandtl number Pr, the variation of the angular velocity with time (ε > 0) on the skin friction and heat transfer rate ue discussed, is shown the figures. It is found that the buoyancy force enhanced both the skin fraction and the heat transfer rate. The effect of the presence of the first resistance decreases the skin friction and the heat transfer rate.

6

Double diffusive convection in a high porosity anisotropic porous medium with externally regulated darcy and brinkman frictions

60%

Siddheshwar P. G. , Vanishree R. K.

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2011

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tom Vol. 16, no 4

1147-1168

EN

A linear stability analysis is performed on the double diffusive porous system using the Rayleigh-Ritz technique. The condition for direct and Hopf bifurcations is obtained as a function of the parameters of the problem. A unique feature in this problem is that Darcy and Brinkman friction are temperature-dependent and hence are amenable to regulation. The study reveals that this external regulation of convection results in a preference for stationary convection over oscillatory mode. A low-porosity medium results for "finger" and "diffusive" instabilities are also discussed in the case of constant viscosity liquids.

7

Combined heat and mass transfer on non-Darcy natural convection in a fluid saturated porous medium with thermophoresis

60%

El-Hakiem M. A. , El-Kabeir S. M. , Rashad A. M.

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2007

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tom Vol. 12, no 1

9-18

EN

The present investigation deals with the combined heat and mass transfer with the effects of thermal dispersion, radiation on non-Darcy natural convection in a fluid saturated porous medium with thermophoresis. The goveming equations, reduced to local similarity boundary layer equations using suitable transformations are obtained. Forchheimer extension is considered in the fIow equations. The coefficient of thermal diffusivity has been assumed to be the sum of molecular diffusivity and the dispersion thermal diffusivity due to mechanical dispersion. Rosseland approximation is used to describe the radiative heat fIux in the energy equation. For the fluids having the Lewis number Le=l.O, 10.0, numerical values of the local Stanton number are presented in a tabular form for different values of the thermophoretic parameter [...], thermal dispersion and thermal radiation for the two cases of Darcy and non-Darcy porous medium. The concentration distributions are show n graphically for various values of the thermophoretic parameter, thermal dispersion and thermal radiation.

8

Prawidłowe chłodzenie szaf sterowniczych Cz.2

60%

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2009

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tom nr 11

32-35

9

Przybliżenie bezpośredniego oddziaływania w problemie konwekcji turbulentnej

60%

Icha A.

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2008

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tom T. 5, nr 36

143-150

PL

W pracy przedstawiono statystyczne ujęcie problemu rozwiniętej turbulencji w stratyfikowanym termicznie i zasoleniowo przepływie turbulentnym. Wykorzystując przybliżenie bezpośredniego oddziaływania (DIA), wprowadzone przez R. Kraichnana, otrzymano zamknięty układ równań dla funkcji korelacji i funkcji odpowiedzi opisujący dynamikę ruchów małoskalowych w podprzedziale bezwładnościowym przy skalowaniu Bolgiano.

EN

In this paper Kraichnan’s Direct Interaction Approximation (DIA), which is an one loop perturbation expansion, is applied to turbulent convection problem. The scaling law of Bolgiano is considered as an approximate solution of the DIA equations for the intertial range of thermally or density stratified fully developed turbulence.

10

Studium konwekcyjnego ruchu powietrza nad powierzchnią ogrzewanej płyty metodą symulacji numerycznej

51%

Trzciński P.

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2006

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tom Nr 6s

243-244

EN

Elaboration of a numeric model describing convectional heat transfer in the system consisting of warmed plate source and enclosing air was the aim of this work. The two-dimensional temperature field, vorticity, stream function and velocity distribution were presented. Convectional movement was modelled using the MRS method in the MATLAB environment programme. Key words: convection, MRS, stream function, vorticity

11

Numerical solutions for heat and mass transfer effects of an unsteady MHD free convective flow past an infinite vertical plate with constant suction (injection) and heat source

51%

Ambethkar V.

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2009

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tom Vol. 14, no 1

67-89

EN

The objective of this work is to study heat and mass transfer in an unsteady MHD free convective flow past an infinite vertical plate with constant suction (injection) and heat source numerically. Dimensionless governing equations of the problem have been solved by using the finite difference technique. Numerical solutions for temperature, velocity, concentration have been obtained for suitable parameters like the Grashof number, mass Grashof number, Prandtl number, Schmidt number and Eckert number. The rates of heat transfer and mass transfer are studied. The results obtained are discussed with the help of graphs and tables to observe the effect of various parameters concerned in the problem under investigation. Effects of suction, the Eckert number and heat source parameter on velocity and temperature distributions are discussed. Stability and convergence of the finite difference scheme is established.

12

Heat teransfer coefficient for F.E. analysis in the warm forging process

51%

Kang J. H. , Lee K. O. , Kang S. S.

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2007

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tom Vol. 20, nr 1-2

367-370

EN

Purpose: The purpose of this paper is to obtain suitable convection and contact heat transfer coefficient for one-time finite element analysis in the warm forging process. Design/methodology/approach: To do this, the temperature of the tool used in the operation was measured with a thermocouple and repeated finite element analysis (FEA) was performed using the experimentally calculated contact at cooling heat transfer coefficient. Also the surface temperature of the active tool was obtained by comparing the measurement and analysis results and finally the contact heat transfer coefficient for one-time FEA was completed by comparing the surface temperature between the repeated FEA and one-time FEA results. Findings: The acceptable convection heat transfer coefficients are from 0.3 to 0.8 N/mm/s/K and the contact heat transfer coefficient of 6-9 N/mm/s/K is appropriate for the warm forging process with flow-type lubrication conditions. Practical implications: A comparison of the temperatures from the repeated and one-time analysis allows an optimum contact heat transfer coefficient for the one time finite element analysis to be determined. Originality/value: several studies have been conducted with diferent conditions such as applied pressure and kind of lubricant, but no research has been conducted concerning the convection heat transfer coefficient in the warm forging process. Also, comparative analysis concerning the reason for difference between experimentally determined contact heat transfer coefficient and practically adapted one has been conducted, yet.

13

The Numerical Simulaton of the Heating Sub-Areas of a Traditional Cupola and Heat Losses to the Environment

51%

Gradowski A.

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2009

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tom Vol. 54, iss. 4

1173-1182

EN

The present paper focuses on the idea of the numerical analysis of the heating processes of the sub-areas of a cupola. The calculation algorithm is based on the radial, single-dimensional model. The developed numerical model includes the conjugation of thermal conduction, free convection and radiation processes in the examined system. This enables the analysis of the variation of the broad range of parameters that describe the course of thermal exchange in the examined system. Definitions of new heat parameters were introduced to facilitate the multi-variant heat and economic analysis of the cupola process. The developed numerical model enabled the construction of a program for a computer simulation of the process under investigation. The results of numerical experiments were compared to the data available in literature [2].

PL

Praca zawiera koncepcje numerycznej analizy procesu nagrzewania podobszarów żeliwiaka tradycyjnego. Algorytm obliczeniowy oparto na modelu radialnym, jednowymiarowym. Skonstruowany model numeryczny ujmuje sprzężenie zachodzących w badanym układzie procesów przewodzenia ciepła, konwekcji swobodnej i promieniowania. Umożliwia analizę zmienności podstawowych parametrów opisujących przebieg wymiany ciepła w badanym układzie. Wprowadzono definicje nowych parametrów cieplnych, ułatwiających wielowariantowa analizę cieplna i ekonomiczna przebiegu procesu żeliwiakowego. Opracowany model numeryczny umożliwił skonstruowanie programu komputerowej symulacji badanego procesu. Wyniki eksperymentów numerycznych porównano z danymi uzyskanymi przez autorów pracy [2].

14

Różnicowy schemat do określania temperatur w cienkowarstwowym akumulatorze betonowym

51%

Sałaciński B. , Pisarev V.

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2008

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tom z. 48 [254]

69-80

PL

Opisano metodę wyznaczania jednowymiarowego wewnętrznego rozkładu temperatur w cienkowarstwowych, betonowych akumulatorach ciepła ochładzanych wewnętrznie i poddawanych jednoczesnemu działaniu zewnętrznego promieniowania słonecznego oraz konwekcyjnej wymiany ciepła.

EN

The paper describes a method of determining one dimensional temperature field in plain (without inner placed pipes with flowing refrigerant) and interior cooled, thin, concrete accumulator of energy which simultaneously receives energy from the solar radiation and convection.

15

Badania nieustalonego przewodzenia ciepła w cienkowarstwowym betonowym akumulatorze energii przy jednoczesnym oddziaływaniu promieniowania słonecznego i konwekcyjnej wymianie ciepła

51%

Sałaciński B. , Pisarev V.

|

2008

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tom z. 48 [254]

55-67

PL

Przedstawiono wyniki symulacji nieustalonego, jednowymiarowego przewodzenia ciepła w betonowym, cienkowarstwowym akumulatorze energii. Symulacje wykonane zostały w programie "Akumulator" dla czterech miesięcy roku. Obliczenia uwzględniały, że akumulator poddawany jest jednoczesnemu działaniu zewnętrznego promieniowania słonecznego oraz konwekcyjnej wymianie ciepła.

EN

The paper presents results of a transient, one dimensional heat conduction simulation in a thin, concrete accumulator of energy. The simulation was carried out using the "Accumulator" program regarding four months of the year. Calculations have also taken into account that the accumulator simultaneously receives energy from the solar radiation and convection (both parameters were constantly changing in time).

16

The exact solution of nonlinear stress-free convection under the influence of magnetic fields

51%

El-Kholy S. A.

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2004

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tom Vol. 7, nr 2

13-22

EN

This paper aims at transforming nonlinear equations (Navier-Stokes, energy and magnetic induction) in steady state into ordinary high order differential equations. The exact solution for it has been found using a suitable transformation. The second goal is studying the state conditions of heating from below in a horizontal layer and studying the influence of the magnetic field on the phenomenon of convection itself. This model paper has uncovered the properties of electricity-conducting fluid elements. These properties have been disclosed neither in theory nor in practice. This study has been applied on the stress-free boundaries. All of which have realistic manifestation, in nature. They study convection in geophysics and astrophysics. Results have been illustrated in three dimensions to generalize the study and use it practically.

17

Axisymmetric MHD oscillation of a compressible hollow jet

51%

Radwan A. E. , Eltaweel M. A.

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2004

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tom Vol. 7, nr 2

127-130

EN

The capillary oscillation of compressible hollow Jet under the action of the electromagnetic force for axisymmetric perturbation is discussed. Some published results are recovered as limiting cases on utilizing the dispersion relation of the present model. The capillary force has a destabilizing effect in a small range (0 ≤ χ < 1, where χ is the dimensionless longitudinal wavenumber) of perturbation. While it is stabilizing as 1 ≤ χ < ∞. The compressibility has a strong destabilizing tendency of the model for all wavenumber values χ ≠ 0. Each of the magnetic fields pervaded in the gas and liquid regions has a stabilizing effect for all short and. long wavelengths. As that effect is so strong, the capillary instability is suppressed and stability sets in. But in fact here the model is unstable due to the strong destabilizing effect of the compressibility.

18

Effect of magnetic field dependent viscosity and rotation on ferrothermohaIine convection in the presence of dust particIes

51%

Sunil , Sharma A. , Shandil R. G.

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2007

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tom Vol. 12, no 1

197-213

EN

This paper deals with the theoretical investigation of the combined effect of magnetic field dependent (MFD) viscosity and rotation on ferrothermohaline convection in the presence of dust particles subjected to a transverse uniform magnetic field. For a flat fluid layer contained between two free boundaries, an exact solution is obtained using a linearized stability theory and normal mode analysis method. The cases of stationary convection and oscillatory modes have been discussed. In this paper, an attempt is also made to obtain the sufficient conditions for the non-existence of overstability.

19

Transient unsteady natural convection MHD flow past a semi-infinite verticaI plate with constant heat flux

51%

Palani G. , Ganesan P.

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2007

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tom Vol. 12, no 1

125-134

EN

A numerical analysis is performed to study the MHD flow of an electrically conducting, incompressible, viscous fluid past a semi-infinite vertical plate with constant heat flux, subjected to a transversely applied magnetic field. The heat due to viscous dissipation and the induced magnetic field are assumed to be negligible. The dimensionless goveming equations are unsteady, two-dimensional, coupled, and non-linear. A most accurate, unconditionally stable and fast converging implicit finite difference scheme is used to solve the non-dimensional goveming equations. Velocity and temperature of the flow have been presented graphically for various parameters. The local and average skin friction and Nusselt number are also presented graphically.

20

Mixed convection heat and mass transfer in a doubly stratified non-Darcy porous medium

51%

Murthy P. V. S. N. , Mukherjee S. , Krishna P. V. S. S. S. R. , Srinivasacharya D.

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2007

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tom Vol. 12, no 1

109-123

EN

The mixed convection heat and mass transfer from a vertical surface embedded in a doubly stratified nonDarcy porous medium have been analyzed. The wall temperature and concentration are constant and the medium is linearly stratified with respect to both temperature and concentration. The external flow is assumed to be uniform. A series approximation is made for both temperature and concentration in terms of the stratification parameter and the solution is presented in both the aiding and opposing flow cases. The flow, temperature and concentration fields are effected by complex interactions among the diffusion ratio Le and buoyancy ratio N and stratification ratio Sr in addition to the flow driving mixed convection parameter Ra/Pe The effect of double stratification of the medium on non-dimensional heat and mass transfer coefficients is discussed.