Filtration performance and loading capacity of nano-structured composite filter media for applications with high soot concentrations

The investigation of filtration and loading performance of fibrous filters with different structures is of high importance for designing filters with long lifetime used in applications with high soot concentrations. Penetration of the soot agglomerates and NaCl particles (with the mobility diameters of 50, 80, 100, 200 and 300 nm) through two types of composite filter media (with the nanostructured layer of electrospun nanofibers and PTFE membrane, respectively) was analyzed. Meanwhile, evolution of the experimental and modeled pressure drop during the particles loading process at the velocities of 6.7 and 11.1 cm/s was also studied. The cake thickness was measured by a new and non-contact method utilizing a 3D optical profiler which would not alter the cake structure. The results showed that the soot penetration was lower than that of NaCl particles under the same condition, because the soot agglomerates had larger effective interception length than the NaCl particles with the same mobility diameter. The pressure drop of the filters loaded with soot agglomerates increased faster than that with NaCl particles. Furthermore, the pressure drop increased faster at the velocity of 11.1 cm/s because of formation of more compact cake. In addition, the pressure drop of the filter with a lower solidity nanostructured layer increased slower because more particles could penetrate into its inner part. The model data agreed with the experimental data well in the case of soot loading. Our results indicate that the filters which have relatively low filtration efficiency against the standard compact aerosol particles yet sufficient efficiency against the soot agglomerates and an open structure can be used in the applications with high soot concentrations to gain a long lifetime.