Numerical Study of Vorticity and Heat Flow in Bottom Heated DDC Systems at Nominal Rayleigh Number

Double diffusive convection (DDC) flows are widely seen in many industrial processes where the thermo-solutal buoyancy forces generates vorticity and initiates convective heat and mass transfer. In this paper numerical computations are conducted on this behaviour inside cavities of different aspect ratio at nominal Rayleigh number using a finite element based code. Velocity-vorticity form of Navier-Stokes equations are solved along with energy and solutal concentration conservation equations simultaneously using Galerkin's weighted residual method. Bottom wall is assumed hot and salted while top wall is maintained as sink, both side walls of the cavity are assumed to be adiabatic to heat and mass flow. Generally cavities with the present boundary conditions exhibit weak vorticity and convection characteristic especially at low Rayleigh number. In this numerical work an attempt is made to explore the role of variation in relative strength of thermal and solutal buoyancy forces on flow characteristics and mode of heat and mass transfer in such conditions. Simulation results have been reported for different buoyancy ratios in the range -2 <= N <= 2, Rayleigh number varying from 1.0e5 to 1.0e3, for cavities of aspect ratios, 0.5(shallow), 1 (square) and 2 (deep). Flow contours are well validated with the results in the literature. The fluid rotation patterns are captured and reported under different operating conditions chosen, the vorticity generation is observed relatively low for deep cavity when compared to other two. Investigations revealed that fluid convection gets greatly hampered when operated in negative buoyancy ratio regime and require relatively higher Rayleigh number to change the mode of heat transfer from diffusion to convection.