Some applications in gas particle separation processes run at low absolute pressures, for example the cleaning of the vapour stream during vacuum drying. Surface filter media are used in this application to allow the recovery of the mostly high-quality products. So far, not much is known about the operating behaviour of filters at low system pressures. Previous studies have been limited to depth filters. The dimensioning of the filters is thus based on data for filtration at ambient pressure. This often leads to incorrectly dimensioned filter sizes. To prevent this, a fundamental understanding of the filtration processes with surface filters at low system pressures is required.

An essential parameter in gas filtration is the pressure drop of unladen surface filter media. In this work, the differential pressure of unladen surface filter media was measured for two different types of filter media with a widely differing structure at two filter face velocities as a function of the absolute pressure. The system pressure was varied in a range of 1 - 1000 mbar. Furthermore, a semi-empirical model was developed that allows the differential pressure of surface filter media to be calculated as a function of the system pressure for the entire Kn-number range...