Wyniki wyszukiwania - BazTech

1

A revised model for the effect of nanoparticle mass flux on the thermal instability of a nanofluid layer

Alharbi Ozwah S., Abdullah Abdullah A.

Demonstratio Mathematica

|

2021

|

Vol. 54, nr 1

488--499

EN

A revised model of the nanoparticle mass flux is introduced and used to study the thermal instability of the Rayleigh-Benard problem for a horizontal layer of nanofluid heated from below. The motion of nanoparticles is characterized by the effects of thermophoresis and Brownian diffusion. The nanofluid layer is confined between two rigid boundaries. Both boundaries are assumed to be impenetrable to nanoparticles with their distribution being determined from a conservation condition. The material properties of the nanofluid are allowed to depend on the local volume fraction of nanoparticles and are modelled by non-constant constitutive expressions developed by Kanafer and Vafai based on experimental data. The results show that the profile of the nanoparticle volume fraction is of exponential type in the steady-state solution. The resulting equations of the problem constitute an eigenvalue problem which is solved using the Chebyshev tau method. The critical values of the thermal Rayleigh number are calculated for several values of the parameters of the problem. Moreover, the critical eigenvalues obtained were real-valued, which indicates that the mode of instability is via a stationary mode.

2

Konwekcja naturalna w modelowym pomieszczeniu z zastosowaniem aproksymacji Bussinesq’a

Radzikowska-Juś W., Owczarek S.

Biuletyn Wojskowej Akademii Technicznej

|

2017

|

Vol. 66, nr 3

75--82

PL

Artykuł przedstawia analizę numeryczną przepływu ciepła w czasie w modelowym pomieszczeniu w wyniku umieszczenia w nim obiektu o podwyższonej temperaturze. W wyniku różnicy temperatur pomiędzy obiektem a otoczeniem w pomieszczeniu następuje zjawisko konwekcji naturalnej. Obliczenia wykonywano z wykorzystaniem oprogramowania ELMER bazującego na metodzie elementów skończonych. W celu zmniejszenia ich złożoności w symulacji wykorzystano aproksymację Bussinesqa. Rozpatrywany przypadek jest zbliżony do konwekcji Rayleigha-Benarda, która stanowi punkt wyjścia dla przeprowadzonej analizy.

EN

The paper presents numerical analysis of heat transfer inside a model chamber in time after entering an object of elevated temperature therein. As a result of the temperature difference between the object and the environment in the room, natural convection has occurred. Numerical simulations were performed using ELMER software based on the Finite Element Method. In order to reduce the complexity of the simulation, the Bussinesq approximation was used. The relevant case is similar to Rayleigh-Benard convection, which was starting point to the conducted analysis.

3

Rayleigh-Bénard convection in an elastico-viscous Walters’ (model B’) nanofluid layer

Rana G. C., Chand R.

Bulletin of the Polish Academy of Sciences. Technical Sciences

|

2015

|

Vol. 63, nr 1

235--244

EN

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.

4

A study of natural convection in anisotropic porous rectangular channels using a thermal non-equilibrium model

Balagondar P. M., Pranesha Setty A.

International Journal of Applied Mechanics and Engineering

|

2012

|

Vol. 17, no. 1

5-16

EN

A study of natural convection in a two dimensional rectangular channel filled with anisotropic porous media is considered, when the fluid and solid phases are not in local thermal equilibrium. Walls of the channel are non-uniformly heated to establish a linear temperature gradient and they are assumed to be impermeable and perfectly conducting. Darcy model with anisotropic permeability is used to describe the flow and a two field models are used for energy equation each representing fluid and solid phases separately. The critical Rayleigh number for the onset of convection using linear stability analysis is obtained numerically as a function of mechanical anisotropy parameters, interphase heat transfer coefficient and aspect ratio, and the same is plotted graphically, and discussed in detail.

5

Rotating Rayleigh-Benard Convection

Majchrowski W., Tuliszka-Sznitko E.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

|

2008

|

Vol. 12, No 3-4

267-272

EN

In the this paper our results on the natural convection in an enclosed rotating cavity are presented. We have focused our attention on the influence of the Rayleigh and Taylor numbers on the flow structure. DNS computations have been performed for the geometry of aspect ratio L=9 and curvature parameter Rm=1.5.

6

The Rayleigh-Benard Convection Analysis by the Lorenz Dynamical System

Jopek H., Strek T.

Vibrations in Physical Systems

|

2004

|

Vol. 21

183--186

7

Rayleigh-Bénard convection with throughflow - a comparative study between the single-term and higher order Galerkin methods

Shivakumara I. S., Suma S. P.

Applied Mechanics and Engineering

|

2000

|

Vol. 5, no 3

507-520

EN

Effects of non-uniform temperature gradient, vertical transport of momentum and vertical transport of perturbation temperature due to throughflow are investigated on the Rayleigh-Bénard convection for different hydrodynamic boundary conditions. The eigenvalue problem for the conducting boundaries is solved by the higher-order Galerkin method. It is shown that the throughflow in one particular direction destabilizes the system depending on the value of the Prandtl number. Also a comparison between the results of single-term and higher order Galerkin methods is made and limitations of the single-term Galerkin method are clearly brought out.

8

Onset of convection in an inclined porous layer with anisotropic permeability

Storesletten l., Tveitereid M.

Applied Mechanics and Engineering

|

1999

|

Vol. 4, no 3

575-587

EN

The present paper is concerned with the onset of Rayleigh-Bénard convection in an inclined porous layer with anisotropic permeability. Due to the temperature gradient and the inclination, a steady shear flow is set up. The critical Rayleigh number at marginal stability of this basic flow is calculated and the flow pattern occurring at convection onset is examined. It turns out that anisotropy in the permeability and the shear flow have an essential influence on the selected flow structure. Depending on the anisotropy ratio and the tilt angle, convection rolls are found either with axes parallel to the basic flow or with axes perpendicular to the flow.