Study of molecular diffusion and natural circulation of a binary gas mixture in a reverse U-shaped tube

The present paper deals with a gas-exchange process of a light gas in a reverse U-shaped tube with a heavy gas outside. The reverse U-shaped tube consists of two vertical pipes; one is at high temperature and the other at low temperature. In order to investigate the gas-exchange process, one-dimensional mole conservation equations for the binary gas mixture and for the gas species and a momentum-conservation equation for the gas mixture are numerically solved to calculate the variation of mole-fraction distributions of species A and B in the reverse U-shaped tube and the onset time of natural circulation of the heavy gas through the reverse U-shaped tube. The calculation is performed for both the cases where the density of the binary gas mixture is approximated and where the density is expressed by the equation of state for an ideal gas