Preliminary Studies on Double-Diffusive Natural Convection During Physical Vapor Transport Crystal Growth of Hg2Br2 for the Spaceflight Experiments

We have conducted a preliminary numerical analysis to understand the effects of double-diffusive convection on the molar flux at the crystal region during the growth of mercurous bromide (Hg2Br2) crystals in 1 g and microgravity (mu g) conditions. It was found that the total molar fluxes decay first-order exponentially with the aspect ratio (AR, transport length-to-width), 1 <= AR <= 10. With increasing the aspect ratio of the horizontal enclosure from AR = 1 up to Ar = 10, the convection flow field shifts to the advective-diffusion mode and the flow structures become stable. Therefore, altering the aspect ratio of the enclosure allows one to control the effect of the double diffusive natural convection. Moreover, microgravity environments less than 10(-2)g make the effect of double-diffusive natural convection much reduced so that the convection mode could be switched over the advective-diffusion mode.