A two-stage cascaded ionizer for boosting PM charging in electrostatic filtration: Principles, design, and long-term performance

In fibrous filtration for airborne particulate matter (PM), the triple wins among efficiency, resistance, and lifetime are hard to achieve owing to the filters' intrinsic geometry. Although charging the PM has been extensively exploited, it is still far from satisfactory for practice, with drawbacks including electrode fouling, ozone, and durability. Herein, based on low-efficiency coarse filters with ultralow pressure drop and potential large dust holding capacity, we bridge this divide by introducing two-stage cascaded ionizers to boost their performance. Enabled by the separated structure for successive ion generation and transport, theoretical design and experimental results demonstrated that the ionizers could efficiently charge the PM and promote filtration efficiencies. The lab-scale prototype composed of the prepared ionizer arrays and polyester (PET) filters stably performed in 25 days, with average daily efficiency of 95.4% for 0.3-0.5 mu m particles, 77.0 g/m2 PM10 accumulating amounts with 4.9 Pa pressure drop, and 56.2 W/m2 power consumption at 1.4 m/s filtration velocity. As the "efficiency boosters" for filters, the ionizers are meanwhile free of PM contamination and possess ultralow ozone generation. We anticipate that our approach will be an efficient, durable, and energy-effective solution in the air filtration community in ventilation systems for clean and sustainable built environments.