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MODIFIED LEWIS NUMBER AND BUOYANCY RATIO EFFECTS ON TURBULENT DOUBLE-DIFFUSIVE CONVECTION IN POROUS MEDIA USING THE THERMAL NON-EQUILIBRIUM MODEL

[+] Author and Article Information
Marcelo J.S. de Lemos

Departamento de Energia − IEME, Instituto Tecnológico de Aeronáutica − ITA, 12228-900 − São José dos Campos − SP, Brazil
delemos@ita.br

Paulo Carvalho

Departamento de Energia − IEME, Instituto Tecnológico de Aeronáutica − ITA, 12228-900 − São José dos Campos − SP, Brazil
energia@ita.br

1Corresponding author.

ASME doi:10.1115/1.4039915 History: Received December 18, 2017; Revised April 02, 2018

Abstract

This work presents a study of double-diffusive free convection in a porous square cavity under turbulent flow regime and with aiding drive. The thermal non-equilibrium model was employed to analyze the energy and mass transport across the enclosure. Governing equations were time- and volume averaged according to the double-decomposition concept. Analysis of a modified Lewis number, Lem, showed that for porous media this parameter presents opposite behavior when varying the thermal conductivity ratio or the Schmidt number, while maintaining the same value for Lem. Differently form free flow, the existence of the porous matrix contributes to the overall thermal diffusivity of the medium, whereas mass diffusivity is only effective within the fluid phase for an inert medium. Results indicated that increasing Lem through an increase in Sc reduces flow circulation inside porous cavities, reducing Nuw and increasing Shw. Results further indicate that increasing the buoyancy ratio N promotes circulation within the porous cavity, leading to an increase in turbulence levels within the boundary layers. Partial contributions of each phase of the porous cavity (solid and fluid) to the overall average Nusselt number becomes independent of N for higher values of the thermal conductivity ratio, ks/kf. Further, for high values of ks/kf, the average Nusselt number drops as N increases.

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