Pseudo-electret filter for micron sized particles in 300°C exhaust gases

The pseudo electret fibres developed at the Applied Electrostatics Research Centre of the University of Western Ontario have been used to build an unlimited life, high efficiency filter for micron sized particles entrained in a 300°C hot exhaust gas. The pseudo-electret fibres used here consist of a close assembly of two submillimetre size fine wires, in which one of the wires is electrically insulated from the other. By applying a low DC potential between these wires 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 fine wires 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 pseudo-electret material made from dual electrode fibre elements. These elements are constructed from seven strands of 100 micron diameter copper wire overlaid with Teflon^TM insulation and wrapped with a spiral of uninsulated copper wire 150 micron in diameter. The filter is able to operate at temperatures up to 300°C while maintaining insulation values between the electrodes of over 500 Mohm with applied potentials up to 500 V. The paper presents the results of the efficiency and pressure drop tests at several values of gas flow, dust loading and air temperature