A Gas Filtration System for Concentrations of 10−5Particles/cm3

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Abstract
Experiments were made to determine the lowest absolute levels of particle concentrations achievable by filtration. Two commercially available PVDF membrane filters were evaluated, namely, a 25-cm pleated filter cartridge (Milli-pore Durapore-TP 1 1Liquid Air is a member of the L'Air Liquide Group. View all notes ) and a smaller point-of-use filter with integrated housing (Millipore Wafergard In-Line 2 2Durapore-TP and Wafergard In-Line are trade marks of Millipore Corp. View all notes ). These filters have established penetration probabilities of less than 3 × 10−9. Tests were performed at steady flow rates up to 1.4 Nm3/min and 0.1 Nm3/min, respectively. Data were taken with a condensation nuclei counter and two laser particle spectrometers. Measurements covering the size range from about 0.01 to 3 μm show that average concentrations of less than three particles/m3 (ca. 0.1 particle/ft3) can be attained continuously. Twenty-four hour periods without detection of a single particle are not uncommon. At these levels, the limiting factor is the cleanliness of all surfaces on the downstream side of the filter, and not filter efficiency in the traditional sense.