Double-Diffusive Mixed Convection and Radionuclides Removals from the Tail Gas Treatment Unit in Nuclear Medicine Building: Multiple Sifting Structures and Porous Medium

Abstract

This paper investigates the effect of porous-media arrangement, hot-plate arrangement, heat flux, and inlet flow on the mixed convection heat transfer, and uniformity of temperature and concentration in an open enclosure. This model is considered for use as an adsorption treatment unit for radioactive waste gas in a nuclear medicine building. The radioactive waste gas flows through the cavity from bottom to top. The two-dimensional governing equations have been solved using the finite volume method. The Prandtl number and aspect ratio of the cavity are fixed at 0.71 and 1, respectively. The problem has been governed by five parameters: −10 ≤ Br ≤ 10, 10−6 ≤ Da ≤ 102, 0.1 ≤ Kc ≤ 10, 10−2 ≤ Ri ≤ 10, and 0.1 ≤ Kr ≤ 10, and the layouts of the porous layer and hot plates. The simulation results indicate that the Type C (polymeric porous media) has excellent heat transfer characteristics with a 10% increase in the Nusselt number (Nu). The contours of streamlines, isotherms and heatlines indicate that, with the increase of Richardson number (Ri), the trend of Nu varies for different arrangements of hot plates. It is interesting to note that the convective heat transfer of Type F (surrounded arrangement) was found to have the lowest Nu number for the same Ri number. The convective heat transfer is more pronounced for Type E (symmetrical arrangement). The Nu number of Type E (symmetrical arrangement) is about 110% higher than that of Type F (surrounded arrangement) and it is about 35% higher than that of Type D (centralized arrangement). This type also has a more uniform temperature distribution, as indicated by the temperature variance. The findings of this study can guide preheating system optimization.

Keywords

• radioactive waste gas
• heat and mass diffusion
• porous media
• computational fluid dynamics
• boundary condition