Abstract
The transient nature of the internal pore structure of particulate wall flow filters, caused by the continuous deposition of particulate matter, makes studying their flow and filtration characteristics challenging. In this article we present a new methodology and first experimental demonstration of time resolved in-situ synchrotron micro X-ray computed tomography (micro-CT) to study aerosol filtration. We directly imaged in 4D (3D plus time) pore scale deposits of TiO nanoparticles (nominal mean primary diameter of 25 nm) with a pixel resolution of 1.6 m. We obtained 3D tomograms at a rate of ∼1 per minute. The combined spatial and temporal resolution allows us to observe pore blocking and filling phenomena as they occur in the filter’s pore space. We quantified the reduction in filter porosity over time, from an initial porosity of 0.60 to a final porosity of 0.56 after 20 min. Furthermore, the penetration depth of particulate deposits and filtration rate was quantified. This novel image-based method offers valuable and statistically relevant insights into how the pore structure and function evolves during particulate filtration. Our data set will allow validation of simulations of automotive wall flow filters. Evolutions of this experimental design have potential for the study of a wide range of dry aerosol filters and could be directly applied to catalysed automotive wall flow filters.
Highlights
In 2018, 82% of urban dwellers still breathed air below the standards set by the World HealthOrganization’s air quality guidelines for particulate matter (PM) [1]
Inspection of the segmented and greyscale images shows that TiO2 deposits are accurately segmented both in deep bed pores and on the surface of the channel wall, see Figure 4
The pore indicated with a red circle is filled with TiO2 deposit during the filtration
Summary
Organization’s air quality guidelines for particulate matter (PM) [1]. Particulate filters are ’wall flow filters’ with channels that run parallel to exhaust gas flow. The blocked channel ends force the exhaust gas to flow through the connected pores in the walls of the particulate filter, from an inlet channel to an outlet channel, filtering out particles. The deposits cause the permeability of the filter to change continuously. Understanding the effects of these pore-scale structural changes, how they choke flow through the filter and how they can be efficiently burnt-off or regenerated is an unmet challenge which requires knowledge of the pore scale 3D distribution of PM deposits over time in particulate filters [3]
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