The aim of this study is to develop a new air cleaning method being applicable to suspended particulate matters (SPM) of wide sizes. We experimentally studied about the effects of a humidity swing operation where sample air is continuously humidified with heating and dehumidified with cooling. The total of SPM concentration of sample air decreased with the humidity swing operation; however, the concentration of SPM from 0.3 to 1 μm markedly increased. Suction flow accompanying condensation, cohesion and thermophoresis were considered as the SPM reduction effects. It would appear that the nano-size SPM grew to submicron size by nuclear condensation and submicron size SPM increased. The experimental results showed that the SPM concentration of 0.3 μm or less decreased by 89% and the total of that decreased by 80%. The applicability of the humidity swing operation to removal of SPM including nano size SPM was shown by the results. Also, exponential reduction of the SPM concentration was demonstrated with applying the repeated humidity swing operation in a circulation air-cleaning apparatus. This method is expected to become effective air cleaning method applicable to wide size range of SPM.

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