Pseudoelectret filter for micrometer-sized particles in exhaust gases at 210°C

The pseudoelectret fibers developed at the Applied Electrostatics Research Centre, University of Western Ontario, London, ON, Canada, have been used to build an unlimited-life high-efficiency filter for micron-sized particles entrained in up to 300°C hot exhaust gas. This pseudoelectret filter has considerable advantages when compared to mechanical or conventional electret-type filters. In a comparable unblinded mechanical filter, the pressure drop is substantially higher, and in a conventional electret filter, the life of the electrical activity of the fibers is limited to hours or days, depending upon environmental conditions. A pseudoelectret fiber consists of a close assembly of two conductors electrically insulated from each other. By applying a low DC potential between the conductors, it is possible to generate a high nonuniform electric field in the air adjacent to their surfaces. This field attracts and retains passing micron-sized particles by the resulting dielectrophoretic force. By reversing the dc polarity periodically every few minutes, the electric field between the two conductors is restored at almost double the initial value due to the combination of the applied dc potential and the charges accumulated during the previous cycle. A prototype cylindrical cartridge air filter has been constructed. The filter media consists of 23 layers of pseudoelectret fibers. These fibers are constructed from seven strands of 100-μm-diameter copper wire overlaid with Teflon insulation and wrapped with a spiral of uninsulated copper wire 150 μm in diameter. The filter is able to operate at temperatures up to 300°C while maintaining insulation values between the electrodes of over 500 MΩ with applied potentials up to 500 V. This paper presents the results of the efficiency and pressure drop tests at several values of gas flow, dust loading, and air temperature