Differences in filtration principles and methods between water filters and air filters

Materials like filter meshes and fibers are used to intercept suspended particles in water. For example, the fiber structure of PP (Polypropylene) cotton filters can block impurities larger than a certain pore size. It is generally used for preliminary filtration to remove large particulate matter such as sediment and rust.

Some activated carbon water filters can absorb organic substances and residual chlorine in water through the porous structure of activated carbon. For instance, the compressed activated carbon filter can effectively adsorb odors and harmful chemical substances in water.

Some special water filters contain ion exchange resins and other materials, which can remove heavy metal ions, calcium and magnesium ions in water through chemical reactions. For example, the ion exchange resin filter used in water softeners can replace calcium and magnesium ions in water to reduce water hardness.

When air flows through the filter, larger particulate matter, due to inertial forces, cannot pass through the filter smoothly with the air flow but instead collide with the fibers of the filter and are captured. For example, in some coarse air filters, the arrangement of the fibers causes the air flow direction to change when passing through, and the particulate matter is intercepted due to inertia.

For very small particles (such as nanometer-sized particles), their Brownian motion in the air is quite obvious. When these particles approach the fibers of the filter, they will spread to the surface of the fibers due to Brownian motion and be adsorbed. This method is effective for capturing tiny particles and plays an important role in high-efficiency air filters.

Similar to the physical filtration of water filters, the fibers of air filters can directly intercept particulate matter in the air. For example, in HEPA (High-Efficiency Particulate Air) filters, the fine fiber structure can intercept more than 99.97% of particles with a size of 0.3 microns.