The Effect of Humidity on Natural Convection in Vertical Air Filled Cavities

The Australian Research Council is funding a project investigating natural convection in cavities filled with unsaturated water vapour-air mixtures. A companion paper (McBain et al., 1996) describes the design of the experimental apparatus to be used in the project.
Previous studies dealt with the case where the gas-vapour mixture in a cavity is saturated. This paper describes preliminary numerical analyses for a cavity with vertical isothermal and isohumid walls, where the vapour pressure on one or both of the surfaces is less than saturation.
Following comparison of the results from the code for a single phase component with a bench mark result, the saturated case is solved for two situations viz. where condensation occurs in the fluid and where the fluid is supersaturated.
Finally, a number of cases are shown where the states of the hot and cold walls ensure unsaturated mixtures within the cavity. Depending on these states, the buoyancy ratio, N, which compares the temperature and concentration buoyancy forces, can be positive or negative. The result of the runs is that the overall energy transfer rates can be up to two orders of magnitude higher than for the heat transfer only case with the same wall temperatures, or reversed with net energy transfer from cold to hot wall.