Density-gradient water-based air filters: Gas/solid-permeable and liquid-impermeable design

Abstract

A water-based air filter (WAF) composed of an inner cylindrical hydrophilic filter and an outer hollow cylindrical hydrophobic filter was installed in an output chamber filled with water. The WAF with water (WAF-WW) showed outstanding recyclability (average PM2.5 RE = 96.5 %) for up to 100 cycles with consistent long-term performance (ΔREmin and max = 1.4 %) and low pressure drops (ΔP1st and 100th = 3 Pa), which were better than those of commercial HEPA filters (H13) (average PM2.5 RE = 96.2 %, ΔRE = 4 %, and ΔP = 21 Pa), at similar PM2.5 concentrations (1,721 μg/m3) and air velocities (0.92 m/s). The WAF-WW also exhibited excellent recyclability up to the 50th cycle with fast and complete removal (HCHO REat 2-13 min = 100 %) of HCHO gas at very low concentrations (0.08–4.98 ppm). Furthermore, since small PM0.3/PM2.5 particles and total volatile organic compound (TVOC) that are hardly filtered by air filters can be easily and quickly removed by the WAF-WW due to the water filter, this is another extraordinary benefit of the wet process over the dry process.