This paper is dedicated to numerical simulation for diffusion-advective convection in a square cavity duringphysical vapor transport of Hg2Br2. Flow characteristics of the temperature difference between the source and crystal regions, 50°C (300°C→250°C), partial pressures of component argon of 20 Torr and 100 Torr are investigated and presented as velocityvectors and streamlines, isotherms and iso-mass concentrations contours. Moreover, alterations of average Nusselt and averageSherwood numbers with (a) the source and crystal regions, (b) the pressures of component argon of 20 Torr and 100 Torrare analyzed and addressed in details. Both average Nusselt and average Sherwood numbers are seen to decrease with theincreasing values of the partial pressures of component argon. Also, it is found that for the two different partial pressuresof component argon, average Nusselt numbers at the source region are greater than at the crystal region, and inversely,average Sherwood numbers at the crystal region are greater than the source region by a factor of 3.