Abstract
A method for testing membrane gas filters having very high collection efficiency has been developed. These filters have high pressure drop together with their high collection efficiency. As a test aerosol, NaCl and ZnCl2 particles generated by an evaporation-condensation type aerosol generator were used. They had a geometric standard deviation ranging from 1.1 to 1.4. These aerosols were supplied into pressurized clean air (about 3 × 104 Pa gauge) by use of an ejector to overcome the pressure of the filter. Because of extremely low aerosol concentrations at the filter outlet, a high-flow rate CNC (condensation nucleus counter: 1 to 2 l/mm) which can detect aerosols of very low concentration was used. Measurement of the filter performance showed that the penetration by particles depended upon the structure of the membrane, but not upon pressure drop. As an example, a penetration of about 2 × 10–10 for 0.02 μm diameter particles at a pressure drop of 3.1 × 104 Pa gauge and a filtering velocity of 0.68 m/s has been observed.
