Fractional Efficiency Test

Particle Technology Laboratory (PTL) can measure fractional filtration efficiency, which provides filtration efficiencies for each particle size from 30 to 300 nm. With this fractional filtration efficiency curve, more detail information can be analyzed since different particle size can be affected by different filtration mechanisms, like diffusion, impaction, interception and electrostatic force. Also, the fractional filtration efficiency can provide the most penetrating particle size (MPPS) of the test filter, which cannot be detected by any other test methods. The figure below shows the filtration test setup for respirator filter media, which can measure fraction filtration efficiency and pressure drop across the test filter media. The setup consists of a Collison type atomizer to generate test solution droplets (NaCl), a diffusion dryer to convert the atomized droplets into polydisperse solid particles. The polydisperse NaCl aerosol will then be passed through a Differential Mobility Analyzer (DMA) so that a monodisperse fraction can be extracted. The challenge particle size in this test ranges 30 to 300 nm. The efficiency of the filter will be calculated by measuring particle counts in the upstream and the downstream of filter media using a Condensation Particle Counter (CPC). Pressure drop across the test filter can be measured by a differential pressure gauge connected to the upstream and the downstream of the test filter (not shown in the figure).