Air Cleaning Method With Humidity Swing Operation for Reducing Suspended Particulate Matters

SPM (suspended particulate matters) removal effects of a humidity swing operation where sample air is continuously humidified with heating and dehumidified with cooling were experimentally studied. The experimental results showed that the humidity swing operation reduced SPM ranging from nanometer to micrometer sizes due to multiple phenomena such as suction flow accompanying condensation and thermophoresis, and the total SPM concentration decreased by 80% under the maximum humidity swing condition. The removal mechanisms were theoretically estimated. It was estimated that contributions of the suction and thermophoresis are significant, gravitational sedimentation works above 5 μm size, and the effect of inertial collision is insignificant. Nuclear condensation that markedly changes the SPM size distribution would not be an effective SPM removal effect. The sum of the theoretical estimations is smaller than the experimental result, and study for clarifying the removal mechanisms is necessary. It was also experimentally confirmed that the SPM reduction effects have no dependence on the concentration. The SPM removal experiment in a circulating system was also conducted. With repeatedly applying the humidity swing operation, the SPM concentration for whole size ranges exponentially decreased and converged at certain value. SPM generation by a mechanical pump might occur. With improving the apparatus, this method is expected to become an effective SPM removal method applicable for the SPM from nanometer to micrometer size.