Buoyancy driven flow of light gases in atmosphere compared to that of hot gases

The transient formation and subsequent dispersion of the plumes of a fixed mass of lighter than air gases emerging out of open cylindrical enclosures with negligible pressure difference was investigated using 3-D and 2-D CFD models. Subsequently, the dispersion into atmosphere of a similar amount of equally buoyant hot air was also considered. The structure and dynamics of the resulting thermally driven hot air plumes were compared to the corresponding characteristics of the mass-transfer driven isothermal plumes. Some cases were investigated in which the dispersing gases were both lighter than air and at a different temperature from that of the atmosphere. The similarities and differences of these double heat-mass-transfer driven problems with the other cases were discussed. It was shown that a criterion developed previously for judging the validity of the 2-D model relative to the more complex 3-D approach for mass-transfer driven problems could be equally applied for the thermally driven or double heat and mass-transfer driven plume flow characteristics.