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Journal of Enhanced Heat Transfer
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ISSN Druckformat: 1065-5131
ISSN Online: 1026-5511

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Journal of Enhanced Heat Transfer

DOI: 10.1615/JEnhHeatTransf.2018024511
pages 399-419

THE EFFECTS OF POROSITY AND MASS-TO-THERMAL DRIVE RATIO ON AIDING AND OPPOSING CONVECTION IN POROUS ENCLOSURES

Marcelo J. S. de Lemos
Departamento de Energia – IEME, Instituto Tecnológico de Aeronáutica – ITA,12228-900 São José dos Campos SP, Brazil
Head of Departamento de Energia (http://mec.ita.br/energia/)Head of Computational Transport Phenomena Laboratory (http://lcft.mec.ita.br/
Paulo H.S. Carvalho
Departamento de Energia − IEME, Instituto Tecnológico de Aeronáutica - ITA 12228-900 - São José dos Campos - SP, Brazil

ABSTRAKT

This work presents a study on double-diffusive free convection in a porous square cavity saturated with a Newtonian fluid under laminar flow simulated with the thermal equilibrium model. Transport equations are discretized using the control-volume method and the system of algebraic equations is relaxed via the SIMPLE algorithm. The effect of Ram and porosity on average Nusselt and Sherwood values was investigated. Results show that as Ram increases, both Nusselt and Sherwood numbers increase, indicating enhancement of heat and mass transfer across the cavity. Further, when the Lewis number is increased while keeping the same thermal properties, reduction of mass diffusivity further enhances flow recirculation for aiding flows (N = 1) within the cavity, which leads to a further increase in Nuω and Shω. When varying the buoyancy ratio N from aiding (N > 0) to opposing flow (N < 0), simulations indicate that when both drives are of equal strength, minimum values for Nusselt and Sherwood occur for N = −1, regardless of Ram. For larger values of |N|, aiding drives will promote fluid rotation in the clockwise direction, for the gradients of T and C applied here, whereas for opposing flows, the fluid rotates in the counterclockwise direction for opposed conditions at the lateral walls. Porosity and thermal conductivity ratio also affect Nuω and Shω.


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