The effects of porosity and mass-to-thermal drive ratio on aiding and opposing convection in porous enclosures

Resumo

© 2018 by Begell House, Inc.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 Nuw and Shw. 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 Nuw and Shw.

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