2014 Volume 22 Issue 3 Pages 47-57
Although the humidity swing air cleaning method experimentally showed the removal effect of the SPM (Suspended Particulate Matter) at over 97% level, the SPM removal mechanism has not been clarified. Thus, the removal effect has been theoretically studied based on the heat and mass transfer during dehumidification of hot saturated moist air. The removal ratios of three phenomena such as a suction flow with diffusiophoresis, thermophoresis and a nuclear condensation inducing gravitational settling were derived analytically. The suction flow and thermophoresis were analyzed based on the diffusion mass transfer of steam and heat transfer in a rectangle dehumidification duct. The nuclear condensation inducing settling was analyzed by combining a supersaturation model, a liquid drop growth model and a gravitational settling model. The results show following conclusions. The suction flow and the thermophoresis contribute only a few tens percent of the total SPM removal effect. On the other hand, the nuclear condensation inducing settling can remove the all SPM under the condition used in the previous experiment. The analysis can reproduce the SPM survival characteristics resembling the exponential decay observed in the experiment by introducing a distribution function to the supersaturation model. These indicate that the nuclear condensation inducing settling can be the dominant mechanism of the SPM removal effect in the humidity swing air cleaning method. It is also shown that the removal effect of the nuclear condensation inducing settling is strongly influenced by flow velocity and the dimensions of the duct in contrast to the suction flow and the thermophoresis. The removal effect reduces proportionally with the flow velocity and height of the duct, and increases with the width and length of the duct. The analysis provides a direction of improving the humidity swing air cleaning method.
