DETERMINATION OF THE FRACTIONAL EFFICIENCIES OF FIBROUS FILTER MEDIA BY OPTICAL IN-SITU MEASUREMENTS

An experimental setup is introduced to determine the fractional effici ency of fibrous filters. The device includes two optical particle coun ters for the in situ measurement of the particle flux and size upstrea m and downstream of a test filter. The simultaneous measurement in the raw and clean gas by a counting method allows a rapid determination o f the fractional efficiencies of various filter media within a few min utes. In the first experiments performed with different aerosols (late x spheres, bacterial aerosol, limestone dust) the apparatus proved to be a reliable instrument for the investigation of the collection behav iour of fibrous filters influenced by various parameters. The fraction al efficiency yields more information about the filter performance, i. e., respirable fraction, collection minimum, particle bouncing off etc ., than the total collection efficiency. Thus it is possible to compar e different filter media of the same or different filter class and det ermine their optimum operational conditions.