Influence of the Dufour effect on convection in binary gas mixtures

Hollinger, St.; Lücke, M.

doi:10.1103/physreve.52.642

Cited by 52 publications

(13 citation statements)

References 27 publications

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“…The results presented above can be compared with the linear stability analysis for this system [13,14,16]. For L 10 22 and c 20.24, the critical Rayleigh number is predicted to be r c 20.017.…”

Section: (Received 28 October 1997)mentioning

confidence: 94%

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Convective Instability in a Fluid Mixture Heated from Above

Porta

Surko

1998

Phys. Rev. Lett.

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Convection patterns in ethanol-water mixtures with negative c are studied when the fluid is heated from above. Although the linear analysis predicts that the instability occurs at zero wave number, a large wave number pattern is observed. The onset is supercritical with a threshold that is experimentally indistinguishable from zero. The convection amplitude exhibits damped oscillations for sudden change in the forcing parameter. At the constant Rayleigh number the patterns first coarsen, then exhibit growth of narrow plumes. The instability appears to be related to salt fingering. [S0031-9007(98)05952-3] PACS numbers: 47.20.Bp, 47.20.Ky, 47.54. + r When a fluid mixture is driven far from equilibrium by the flow of heat or material into one or more surfaces of the fluid volume, the system may become unstable to a convective flow which enhances the material and heat transport. There are many important examples of this type of flow in nature and technology. For instance, thermohaline convection in the oceans can be driven by temperature gradients or by salinity gradients [1], and double diffusive convection can be important in crystal growth. Finally, convection in fluid mixtures continues to be an important model system for the study of pattern formation in systems driven far from equilibrium [2].In this Letter, we describe experiments on convection in a fluid mixture with negative separation ratio in which the fluid is heated from above, a regime of parameters which has not been studied extensively. We find that a short wavelength convection pattern appears, despite the fact that the linear instability occurs at zero wave number. The onset of the pattern appears to be supercritical bifurcation to a steady flow, although damped oscillations in the pattern amplitude are observed when the forcing parameter is changed rapidly. The patterns continue to undergo stochastic motion even after they have reached a statistically stationary state.The experiments were performed in the RayleighBénard configuration, in which a thin layer of fluid mixture is confined between horizontal plates which are held at a fixed temperature difference. The thermal driving of the system is characterized by the Rayleigh number,where n is the viscosity, k is the thermal diffusivity, g is the acceleration of gravity, a is the thermal expansion coefficient, and h is the cell height. (Below, we will use the reduced Rayleigh number, r ϵ Ra͞1708, which is normalized to the onset of convection in a pure fluid.) In principle, it would be simplest to impose similar boundary conditions on temperature and concentration by fixing the concentration difference between the top and bottom plates. In laboratory experiments, however, the system boundaries are typically impermeable to both components of the fluid mixture, so that only the average concentration of solute in the fluid is directly controllable. The Soret effect introduces a coupling between concentration transport and the local temperature gradient in the mixture, and this causes a concentration...

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Section: (Received 28 October 1997)mentioning

confidence: 94%

“…The linear stability analysis predicts that the critical wave number is zero [16], although further investigation has revealed that a broad spectrum of wave numbers becomes unstable slightly above threshold [14]. The initial patterns, such as the one shown in Fig.…”

Section: (Received 28 October 1997)mentioning

confidence: 99%

Convective Instability in a Fluid Mixture Heated from Above

Porta

Surko

1998

Phys. Rev. Lett.

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“…The governing equations are solved in ANSYS Fluent. The assumptions are taken for CFD modeling: the steady‐state conditions; no flux of energy due to a mass concentration gradient (no Duflor effects); work by viscous forces and by pressure is not done.…”

Section: Cfd Modelingmentioning

confidence: 99%

Flow dynamic in a packed bed filled with Ni‐Al₂O₃ porous catalyst: Experimental and numerical approach

Pashchenko

2019

AIChE Journal

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Numerical simulations and experiments have been carried out to explore the effect of particle shapes on the pressure drop and the loss factor in a packed fixed bed filled with a porous catalyst. The packed bed is presented by the Ni‐Al2O3 catalyst of the different shapes. The commercial program ANSYS Fluent is used for the analysis; more than 20 mln cells are used for computational fluid dynamics (CFD) modeling. The catalyst particles were set as a porous medium with the viscous resistance coefficients and the inertial resistance coefficients. The comparison of the pressure drops between the experimental and simulation results show a good correlation with the divergence of results <8%. To determine the effect of the porosity properties of the medium on the numerical results, two cases of CFD modeling were realized (with taking into account the porous medium properties and without it). The discrepancy between results increases with an increasing gas flow rate.

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“…In presented CFD model the conservation and momentum equations in combination with source term for a porous medium equation are solved in ANSYS Fluent. The assumptions are taken for CFD modeling: steady‐state conditions; the temperature of flow is constant; no the flux of energy due to a mass concentration gradient (no Duflor effects); work by viscous forces and by pressure is not done; surface oxidation reactions of the metal wall are absent.…”

Section: Cfd Modelingmentioning

confidence: 99%

Numerical calculation with experimental validation of pressure drop in a fixed‐bed reactor filled with the porous elements

2020

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To study flow dynamics in a fixed‐bed reactor, experiment and numerical simulation are used. In this work, the flow dynamics in a fixed‐bed reactor filled with porous particles was simulated. For verification, experimental data were used. Porous particles were prepared from grains with sizes from 0.2 to 2.0 mm. Porous particles made by sintering grains in a muffle furnace. The study of pressure drop was performed in the velocity range up to 3 m/s. Numerical calculation was performed for a realistic computational domain obtained by RBD‐algorithm (rigid body dynamics). It was found that if the pore size is less than 0.5 mm, then the flow through the porous medium of particles is minimal; if the pore size is larger than 0.5 mm, then there is a flow through the porous elements of the fixed‐bed reactor. To take into account the porosity of the particles, γ correlation coefficient was proposed for the Ergun equation.

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Influence of the Dufour effect on convection in binary gas mixtures

Cited by 52 publications

References 27 publications

Convective Instability in a Fluid Mixture Heated from Above

Convective Instability in a Fluid Mixture Heated from Above

Flow dynamic in a packed bed filled with Ni‐Al₂O₃ porous catalyst: Experimental and numerical approach

Numerical calculation with experimental validation of pressure drop in a fixed‐bed reactor filled with the porous elements

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Influence of the Dufour effect on convection in binary gas mixtures

Cited by 52 publications

References 27 publications

Convective Instability in a Fluid Mixture Heated from Above

Convective Instability in a Fluid Mixture Heated from Above

Flow dynamic in a packed bed filled with Ni‐Al2O3 porous catalyst: Experimental and numerical approach

Numerical calculation with experimental validation of pressure drop in a fixed‐bed reactor filled with the porous elements

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Flow dynamic in a packed bed filled with Ni‐Al₂O₃ porous catalyst: Experimental and numerical approach