PARAMETERS AFFECTING THE LOADING BEHAVIOR AND DEGRADATION OF ELECTRICALLY ACTIVE-FILTER MATERIALS

Electrically active fibrous filters, that is fibrous filters whose fib ers carry a permanent electric charge, are a popular alternative to co nventional fibrous filters in applications where low pressure drop and high collection efficiencies are critical. The advantage of these mat erials is the additional collection efficiency, due to electrostatic m echanisms, that can be achieved without pressure drop increase. Althou gh the efficiency of these materials is always superior to that of a c onventional material of similar structure, the efficiency of these mat erials can fall as they are loaded with particles, so it is necessary that a proper account be taken of this process during use. Significant advances have been made in understanding the mechanisms responsible f or this reduction in efficiency in a recent experimental study of the loading behavior of a mixed fiber type electrically active material. T his study has identified a number of parameters that cause the filtrat ion efficiency to be reduced, and in so doing also has allowed an empi rical equation to estimate the maximum penetration through the materia l over the course of its life to be elucidated. Furthermore, a series of experiments designed to investigate the effects of particle size an d particle charge on filter degradation has been performed that prove conclusively that the reduction in filtration efficiency of this mater ial during loading is not a charge neutralization process. (C) 1998 Am erican Association for Aerosol Research.