The removal effect of a humidity swing operation on suspended particulate matters (SPM) of room air was experimentally studied. The variation of the SPM number between inlet and outlet of an apparatus with a continuous humidification and dehumidification was measured with an optical particle counter. Generally, the filtering method and the electrical-dust-collection method are widely used for the removal of the SPM of sub- to micron-size. At the beginning of this study, the aim was set to investigation of a new SPM removal method using suction flow with condensation of water vapor in moist air. Removal of airborne molecular contaminant and VOC were also expected as well as a humidity control function in the air conditioning system. The experimental results showed that the humidity swing operation increases observable particles and reduces large particles over 5 μm. A large number of liquid droplets were found in observation of collected particles after the humidity swing operation. It was concluded that the nuclear condensation takes place on the SPM in the supersaturation moist air. New whole SPM removal method can be proposed, where the SPM grow to several micrometer sizes by the nuclear condensation by the humidity swing operation, and then the grown particles are easily removed by gravitational sedimentation or an inertial collision method.

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