Double diffusion convection in a cavity with a hot square obstacle inside is simulated using the lattice Boltzmann method. The results are presented for the Rayleigh numbers 10

4

10

5

and 10

6

the Lewis numbers 0.1

2 and 10 and aspect ratio A (obstacle height/cavity height) of 0.2

0.4 and 0.6 for a range of buoyancy number N=0 to -4 with the effect of opposing flow. The results indicate that for |N| 1

the Nusselt and Sherwood numbers decrease as buoyancy ratio increases

while for |N|1

they increase with |N|. As the Lewis number increases

higher buoyancy ratio is required to overcome the thermal effects and the minimum value of the Nusselt and Sherwood numbers occur at higher buoyancy ratios. The increase in the Rayleigh or Lewis number results in the formation of the multi-cell flow in the enclosure and the vortices will vanish as |N| increases.