2014 Volume 22 Issue 1 Pages 11-20
The aim of this study is to develop a humidity swing air cleaning method for removal of suspended particulate matter, SPM, of whole size ranging from nanometer to micrometer in diameter. In the proposed method, air is consecutively humidified with heating and dehumidified with cooling. The removal characteristics of the SPM were investigated with two apparatus: a basic characteristic testing apparatus of 3 L ⁄ min class and a middle size practicality testing apparatus of 30 l ⁄ min class. Each apparatus is composed of a duct, a heating- and evaporation-type humidifier, and a cooling- and condensation-type dehumidifier. The SPM concentration in the tested room air was measured by an optical particle counter and a condensation nuclei counter. The experimental results showed that the survival ratios of the total SPM exponentially decreases with the humidity swing amount, Δx, that is the absolute humidity drop of the air from the humidified state to the dehumidified state. The reduction characteristics of the SPM did not show the concentration dependence in 21 to 9800 particles ⁄cc range. These indicate that the removal ratio is proportional to the Δx and the SPM concentration. Moreover, particle size dependence of the removal effects was small. In addition, the growth of the SPM with nuclear condensation was obviously detected above Δx = 0.1. However, the grown-up size below 1 μm and small fraction to the whole SPM denied the removal enhancement by the gravitational sedimentation. The maximum removal ratio was 97% in the experiment with the middle apparatus at a condition of the air flow rate of 27 L ⁄ min and Δx = 0.16. It demonstrated that the performance of the humidity swing method is in the level of the practical consideration.
