Combination of Single-Photon Emission and X-Ray Computed Tomography to visualize aerosol deposition in pleated filter

We use a combination of Single-Photon Emission Computed Tomography and X-Ray Computed Tomography to visualize the behavior of a radioactively marked aerosol in pleated filters under different operating conditions. We first validate this atypical method as a mean to comprehensively observe the filtration process in a filter at the macroscopic scale. This non-intrusive technique highlights the influence of the filtration velocity on the areas where the particles first tend to settle out in blank HEPA filter. We demonstrate that the pleating geometry and the local media permeability act on the flow and account for the preferential location of the deposit. Moreover, e show that the increase in the filtration rate leads to a more homogeneous distribution of the tracer on the entire height of the pleats and hence a more uniform arrangement of the flow. The rigid separators, placed on the media to increase the effective filtration surface, act as obstacles around which the flow is splitted, thus reducing the available area of filtration. Surface observations of loaded filters show that an inhomogeneous growth of the cake induces the formation of preferential channels for the solid aerosol to flow in. Caution should then be taken when carrying out the tomographic analyses because of the competition between the local air resistance and the local efficiency that can prevent from determining the areas where the radioactive aerosol accumulates.