Ultrafine particle cleaning performance of an ion spray electrostatic air cleaner emitting zero ozone with diffusion charging by carbon fiber

A novel electrostatic precipitator (ESP)-type small air cleaner with an ion spray charger was developed and evaluated. Unlike conventional ESP air cleaners, the charger is located at the rear of the collection stage. Ions are emitted into ambient space by the fan of the air cleaner, and airborne particles are charged by nearby ions through a diffusion charging mechanism. A carbon fiber ionizer without a grounded metal plate was installed as the charger to minimize ozone emission. The novel air cleaner had a particle clean air delivery rate (CADR) for 0.3-mu m particles of 0.863 m(3)/min at a fan flow rate of 2.0 m(3)/min and applied voltages of - 5 kV to the ionizer and collection plate. As the size of the particles increased from 0.25 to 1 mu m, particle CADR increased from 0.6 to 1.6 m(3)/min. Near-zero ozone emission was generated in a closed chamber (30.4 m(3)), and the concentration decreased from an initial background level of 2.39 ppb-1.29 ppb after 12 h of continuous operation. Our study showed a close relationship between particle CADR and the number of charges per particle, and the number of charges per particle matched well with theoretical predictions based on diffusion charging theory. The particle CADR of ion spray ESPs was 3.63 times higher than that of a high-efficiency particulate air (HEPA) filter air cleaner of similar volume. In an actual environment (56.43 m(3)), the particle CADR was 0.798 m(3)/min, similar to the chamber test.