Collection efficiency of sintered ceramic filters made of submicron spheres

The performance of filters made of sintered submicron alumina particles was evaluated. The filter has a high collection efficiency and high pressure drop, requiring the development of a special measuring system for its evaluation. The system consists of a polydisperse NaCl particle generator, a differential mobility analyzer (DMA), an ejector to supply aerosols for testing filters with high pressure drop, and a mixing-type condensation nucleus counter (CNC) capable of obtaining a stable reading of very low concentration particles. Penetrations as low as 10⁻⁹ can be measured in the particle diameter range of 0.02-0.14 μm. Two filters made by sintering 0.60 and 0.84 μm alumina particles were evaluated. The experimental data collected served as the basis of theoretical development. Following the single fibre theory, the filter penetration is calculated by using a single sphere as the element. Both the diffusion and interception collection mechanisms were taken into account. The resulting equation gives a general trend of efficiency curves as a function of the parameters involved, e.g. the test aerosol size, packed particle size and filtration velocity. However, it is not sufficiently accurate for providing quantitative performance results.