The effect of electrostatic forces on filtration efficiency of granular filters

• Determine the effect of electrostatic force on the filtration efficiency of granular filters
• Determine the relation between the separation efficiency due to electrostatic forces and the residence time
• Determine the difference between the charge states of nanoparticles for sub-20 nm particles and larger ones

The effect of electrostatic forces on the granular filtration of nanoaerosol NaCl particles in the range of 10 nm to 100 nm was investigated experimentally in this study. The test granular filters were made of 2 mm homogeneous glass beads at three media thicknesses (25, 76 and 127 mm), and they were tested at three air flow rates (27, 45, and 65 lpm). The filtration efficiencies were measured for neutralized and charged NaCl nanoparticles. The corresponding difference was considered as the filtration efficiency attributed to the electrostatic attraction between the charged NaCl particles and the glass granules. Results showed that the electrostatics played a great role in nanoaerosol filtration, which is different from conventional filtration theories. Its contribution to filtration efficiency increased with the size of the nanoparticles to a level of 30% or so. Results also showed a positive correlation between the separation efficiency due to electrostatic forces and the residence time of the air flow. The correlation is relatively strong (between 0.6 and 0.9) for particles in the range of 20–100 nm. However, it is weak, although positive, for sub-20 nm particles.

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