Article

# Stability analysis of natural convection in porous cavities through integral transforms

Laboratório de Transmissão e Tecnologia do Calor (LTTC), Programa de Engenharia Mecânica, EE, COPPE, Universidade Federal do Rio de Janeiro, Cidade Universitária, Cx. Postal 68503, Rio de Janeiro, RJ, 21945-970, Brazil; Programa de Engenharia Metalúrgica e de Materiais, EE, COPPE, Universidade Federal do Rio de Janeiro, Cidade Universitária, Cx. Postal 68503, Rio de Janeiro, RJ, 21945-970, Brazil

International Journal of Heat and Mass Transfer (Impact Factor: 2.52). 01/2002; DOI: 10.1016/S0017-9310(01)00231-9 -
##### Article: Experimental study of natural convection in horizontally-positioned open-celled metal foams

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**ABSTRACT:**Experimental study of air natural convection in horizontally-pos itioned copper metallic foams with open cells was conducted. Temperature distributions on the heating surface were tested under different heating power for foam samples having different porosities and pore densities. The effects of porosity and pore density on the total thermal resistance of the foam sample were quantified. It is found that the porous surface can enhance the natural convection and reduce the thermal resistance by about 20% in comparison with a smooth surface. The surface area density and mass flow rate in natural convection are affected by porosity and pore density simultaneously. When the porosity is relative small (I: = 90%), there exits a critical value of the Gr number (turning point) for two pore densities (10ppi and 40ppi). When the Gr number is less than this critical value, the foam with a higher pore density has the lower total thermal resistance, whereas when the Gr number exceeds the turning point value, the opposite holds. If the01/2011; - [Show abstract] [Hide abstract]

**ABSTRACT:**Atmospheric air pollution turbulent fluxes can be assumed to be proportional to the mean concentration gradient. This assumption, along with the equation of continuity, leads to the advection–diffusion equation. Moreover, large eddies are able to mix scalar quantities in a manner that is counter to the local gradient. In this work we present a semi-analytical solution for the three-dimensional steady-state advection–diffusion equation, considering non-local turbulence closure using the Generalized Integral Advection Diffusion Multilayer Technique (GIADMT). We report some examples of applications of the new solution for two different datasets and for a water tank experiment.Atmospheric Research 10/2008; · 2.20 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**Stochastic bifurcations and stability of natural convection within two-dimensional square enclosures are investigated by different stochastic modelling approaches. Deterministic stability analysis is carried out first to obtain steady-state solutions and primary bifurcations. It is found that multiple stable steady states coexist, in agreement with recent results, within specific ranges of Rayleigh number. Stochastic simulations are then conducted around bifurcation points and transitional regimes. The influence of random initial flow states on the development of supercritical convection patterns is also investigated. It is found that a multi-element polynomial chaos method captures accurately the onset of convective instability as well as multiple convection patterns corresponding to random initial flow states.Journal of Fluid Mechanics 05/2010; 650:391 - 413. · 2.29 Impact Factor

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