The design of high performance filter media for HEPA and ULPA applications is examined comparing theoretical predictions with experimental data. The analysis employs a hybrid filtration model. Pressure drop and particle collection efficiency in the region of minimum efficiency where particle diffusion is decreasing and particle interception is increasing as the particle size increases are examined as functions of particle diameter, velocity, and media geometry including fiber diameter, solidity, and thickness.
Several grades of filter media are characterized and tested for particle sizes in the region of the point of minimum efficiency at typical media rating and application velocities. Filter media performance comparisons are made that show how the point of minimum efficiency can be altered by velocity and media geometry changes. This information is used for a discussion of HEPA and ULPA media performance rating criteria with respect to test and application conditions.
Based upon the results of this study, filter media design, analysis, evaluation and application tools are presented for optimizing high performance filter media for HEPA applications, with suggested future trends based upon projected needs for improving the performance of HEPA media.