Role of porosity and solid-to-fluid thermal conductivity ratio on turbulent combined heat and mass transfer in a porous cavity

Abstract

Knowledge on the effects of porosity and thermal conductivity ratio on double-diffusive transport are much needed for optimum design and analysis of a number of engineering equipment. So far, the open literature seems to lack specific investigations on the effects of those two parameters on overall heat and mass transfer in cavities. This work contributes to such much-needed study on double-diffusive convection in a porous square cavity. Turbulent flow regime and aiding drive cases were considered. Governing equations were time- and volume averaged. Turbulence was handled with a macroscopic two-equation model. The thermal non-equilibrium hypotheses was employed to analyze energy transport across the enclosure. Mass transport assumes a binary mixture with solute characterized by its mass fraction. Equations were discretized with the control volume method numerically relaxed using the SIMPLE method. Here, two situations are investigated regarding the effect of porosity. First, porosity is varied along with permeability. Second, permeability is fixed while porosity takes different values. Results indicated that reducing both porosity and permeability induced flow recirculation and increased overall heat and mass transfer, leading to higher levels of turbulent kinetic energy. Such effects are less pronounced when permeability was kept constant while varying porosity. Further, increasing the thermal conductivity ratio substantially affected flow recirculation in the cavity, enhancing, ultimately, turbulence and mass transfer.