Wyniki wyszukiwania - BazTech

1

Boundary effects on electrothermal convection in a dielectric fluid layer

Ravisha M., Raghunatha K. R., Mamatha A. L., Shivakumara I. S.

Archives of Thermodynamics

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2019

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Vol. 40, no 1

3--19

EN

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.

2

Compressible analysis of Bénard convection of magneto rotatory couple-stress fluid

Mehta C. B., Singh M.

International Journal of Applied Mechanics and Engineering

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2018

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Vol. 23, no. 1

91--105

EN

Thermal Instability (Benard’s Convection) in the presence of uniform rotation and uniform magnetic field (separately) is studied. Using the linearized stability theory and normal mode analyses the dispersion relation is obtained in each case. In the case of rotatory Benard’s stationary convection compressibility and rotation postpone the onset of convection whereas the couple-stress have duel character onset of convection depending on rotation parameter. While in the absence of rotation couple-stress always postpones the onset of convection. On the other hand, magnetic field on thermal instability problem on couple-stress fluid for stationary convection couple-stress parameter and magnetic field postpones the onset of convection. The effect of compressibility also postpones the onset of convection in both cases as rotation and magnetic field. Graphs have been plotted by giving numerical values to the parameters to depict the stationary characteristics. Further, the magnetic field and rotation are found to introduce oscillatory modes which were non-existent in their absence and then the principle of exchange of stability is valid. The sufficient conditions for non-existence of overstability are also obtained.

3

A dynamically adaptive lattice Boltzmann method for thermal convection problems

Feldhusen K., Deiterding R., Wagner C.

International Journal of Applied Mathematics and Computer Science

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2016

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Vol. 26, no. 4

735--747

EN

Utilizing the Boussinesq approximation, a double-population incompressible thermal lattice Boltzmann method (LBM) for forced and natural convection in two and three space dimensions is developed and validated. A block-structured dynamic adaptive mesh refinement (AMR) procedure tailored for the LBM is applied to enable computationally efficient simulations of moderate to high Rayleigh number flows which are characterized by a large scale disparity in boundary layers and free stream flow. As test cases, the analytically accessible problem of a two-dimensional (2D) forced convection flow through two porous plates and the non-Cartesian configuration of a heated rotating cylinder are considered. The objective of the latter is to advance the boundary conditions for an accurate treatment of curved boundaries and to demonstrate the effect on the solution. The effectiveness of the overall approach is demonstrated for the natural convection benchmark of a 2D cavity with differentially heated walls at Rayleigh numbers from 103 up to 108. To demonstrate the benefit of the employed AMR procedure for three-dimensional (3D) problems, results from the natural convection in a cubic cavity at Rayleigh numbers from 103 up to 105 are compared with benchmark results.

4

A Characterization of the Rivlin-Ericksen Viscoelastic Fluid in the Presence of a Magnetic Field and Rotation

Banyal A. S.

Engineering Transactions

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2012

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Vol. 60, iss. 4

355-355

EN

A layer of Rivlin-Ericksen viscoelastic fluid heated from below is considered in the presence of an uniform vertical magnetic field and rotation. Following the linearized stability theory and normal mode analysis, this paper mathematically establishes the condition for characterizing oscillatory motion, which may be neutral or unstable, for rigid boundaries at the top and bottom of the fluid. It is established that all non-decaying slow motions starting from rest, in the configurations, are necessarily non-oscillatory in the regime TAF 2 + TA 4 + Qp2 2 1; where TA is the Taylor number, Q is the Chandrasekhar number, p2 is the magnetic Prandtl number, and F is the viscoelasticity parameter. This result is important, since it holds for all wave numbers for rigid boundaries of infinite horizontal extension at the top and bottom of the fluid, and the exact solutions of the problem investigated in closed form are not obtainable.

5

Thermal convection in polymer solutions numerical experiment

Stręk T.

Zeszyty Naukowe Politechniki Poznańskiej. Budowa Maszyn i Zarządzanie Produkcją

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2004

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Nr 1

113-130

EN

In thermodynamics of fluids by convective motion it is understood that a fluid flow which, apart from mechanical quantities, is characterized also by thermal and/or other fields. Dimensionless governing equations are presented for this problem. Dimensionless numbers: the Prandtl number, the Rayleigh number and the Eckert number are introduced. In this paper numerical algorithm for solution of thermal convection in polymer is presented. Rheology model used for polymer is the Carreau model of non-Newtonian fluid. Numerical solutions for convective cooling of Carreau fluid in box are presented.

PL

W termodynamice płynów ruch konwekcyjny płynu jest charakteryzowany nie tylko przez wielkości mechaniczne, ale także przez pole cieplne i inne pola. W artykule przedstawiono bezwymiarowe równania opisujące zagadnienie konwekcji termicznej. W równanich tych wykorzystano liczby bezwymiarowe: Prandtla, Rayleigh i Eckerta. Zamieszczono również algorytm numerycznego rozwiązania problemu konwekcji termicznej w polimerach z wykorzystaniem metody elementów skończonych. Model reologiczny użyty do opisu polimerów to model nienewtonowskiego pfynu Carreau. Przytoczono wyniki numerycze konwekcyjnego ochładzania płynu Carreau w kwadratowym obszarze o „nieskończonej" długości.

6

On thermal convection in micropolar fluids in presence of suspended particles

Mohan H., Kumar P., Anjula

Studia Geotechnica et Mechanica

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2002

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Vol. 24, nr 3-4

53--63

PL

Opisano niestabilność termiczną płynów mikropolamych w obecności cząstek zawieszonych. Sprzężenie między ruchem wirowym a strumieniami ciepła może być przyczyną nadstabilnych stanów w układzie. Zawieszone cząstki wprowadzają także drgania w układzie, a wartość liczby Rayleigha zmniejsza się ze zwiększeniem liczby cząstek zawieszonych.

EN

The thermal instability of micropolar fluids in the presence of suspended particles has been considered. The coupling between spin and heat fluxes may bring overstable modes in the system. The suspended particles also introduce oscillatory modes in the system and the Rayleigh number is found to decrease with the increase in suspended particles.