NUMERICAL SIMULATION OF DOUBLE DIFFUSIVE MIXED CONVECTION IN A LID-DRIVEN SQUARE CAVITY WITH FLUX BOUNDARY CONDITIONS

Abstract

In nature and in many engineering applications, there are many transport processes which are governed by the buoyancy forces from both thermal and mass (solutal concentration) processes. This phenomenon is known as thermo-solutal convection or double diffusive convection (in short DDC). DDC phenomena play important role in oceanography, atmospheric science, astrophysics, geology and also in engineering. Out of various engineering applications, nuclear waste repository and chemical vapour deposition (CVD) technique can be regarded as a problem of DDMC with heat and mass flux boundary conditions. The recent advances in computational fluid dynamics (CFD) and computer technology have provided powerful tools to predict the flow characteristic within a cavity that would almost be impossible to evaluate using experimental procedures. When using a CFD simulation, the reliability and accuracy of results depend on several factors, such as the numerical scheme and the modeling of the boundary conditions. Heat and mass flux sources usually co-exist in many engineering processes and hence, the present work aims at studying the DDMC in a lid-driven square cavity with flux boundary conditions numerically. For the sake of simplicity, a two-dimensional laminar mixed convection with only one heat flux and one mass flux source are considered here. The objective of the present work is to investigate the characteristics of the fluid flow and heat/mass transport in lid-driven cavity. The governing equations for fluid, heat and mass transport are coupled and non-linear and hence they have to be solved using numerical solution technique. A computer program in FORTRAN has been developed for simulation trials. A numerical study is carried out by simultaneously varying the characteristic parameters, 100 <_ Re <_ 1000, 0.5 _< Ri <_ 1.0 and —10 <— B <_ 10. Vorticity is generated at the boundaries of the cavity as expected. The results obtained correctly predicted the temperature evolution from the boundary region where the heat flux is provided as boundary condition and due to the thermo-solutal buoyancy forces as well as the inertial force of the top moving lid, the heat is being convected throughout the cavity. These trends are observed from the temperature distribution curves. Similar trends were observed for concentration distributions which are convected due to the evolution of concentration from the mass flux boundary region on the top lid of the cavity. It is observed that, with increasing Ri and Re, average Nu increases from 75% to 200%, whereas with decreasing Ri and increasing Re, average Sh increases from 250% to 300%.