Numerical investigation of turbulent double-diffusive mixed convection in a slot ventilated enclosure with supply air flow ports
Résumé
Double-diffusive convection is encountered in many practical engineering applications such as oceanography, astrophysics and geophysics [1], crystal growth applied to semiconductors, melting and solidification processes in binary mixtures, storage of liquefied gases, underground infiltration of pollutants [2], and so on. Strength of heat and mass sources can essentially influence the transport structures of fluid, heat, and contaminant. When external forced flow is imposed, there may be double-diffusive mixed convection or mixed convection may occur, particularly in enclosures' ventilation which is complex because of the interactions between buoyant-induced fluid flow and forced external convection. To deepen our understanding of heat and mass transfer characteristics, turbulent double-diffusive mixed convection in an enclosure with side venting is numerically studied. Increased awareness of the potential health risks associated with indoor air pollutants has stimulated interest in improving our knowledge of how the ventilated air is distributed and how contaminants are transported within the buildings. The indoor air movement is also an important element for thermal comfort. Therefore, it is necessary to study the distribution of the air in the rooms. To improve the indoor air quality, the ventilation is as one of the promising solutions. Its principle is to renew sufficiently and permanently the exhaust air by fresh air unpolluted. Inside ventilated room, two physical phenomena can occur, namely the natural convection that is induced by the buoyancy forces in the presence of heat sources and contamination, and the forced convection due to external forces in the presence of mechanical ventilation. The combination of these two phenomena leads to the mixed convection. To obtain reliable information concerning the air flow inside ventilated cavities with uniform heat and contaminant (CO2) sources applied on the bottom wall, we carried out a numerical study based on the prediction of the behavior of aero-thermosolutal flows. An external fresh air flow enters at the cavity through an opening located at the right of the left vertical wall and exits from an opening located at the bottom of opposite wall. The vertical and upper walls are fixed at external temperature and concentration. The Reynolds and Rayleigh numbers are fixed at 706 and 2.62×109, respectively. The working fluid is considered as air-CO2 mixture. Numerical simulations are carried out for different values of CO2-source. The validation of the numerical model is performed by comparing our results with experimental data from the literature [3]. The obtained results indicate that the increasing of CO2 source influences slightly the air movement and the ventilation effectiveness for temperature distribution. This is due to the predominance of the thermal buoyancy forces driven by the heat source and the external forces caused by the ventilation. Nevertheless, its role remains important in terms of CO2 distribution and index of indoor air quality. References [1] Sezai, I., Mohamad A. A., Double diffusive convection in a cubic enclosure with opposing temperature and concentration gradients. Phys. Fluids 12 , 2210-2223, 2000. [2] Serrano-Arellano, J., Xamán, J., Álvarez, G., Gijón-Rivera, M., Heat and mass transfer by natural convection in a square cavity filled with a mixture of Air?CO2. Int. J. Heat Mass Transf. 64, 725-734, 2013. [3] Blay, D., Mergui, S., Niculae, C., Confined turbulent mixed convection in the presence of horizontal buoyant wall jet, Fundamentals of Mixed Convection, Heat Transf. Div. 213, 65-72, 1992.
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