Accumulator, Transporter, Substrate, and Reactor: Multidimensional Perspectives and Approaches to the Study of Bark

Woody ecosystems have a relatively thin but aerially extensive and dynamic layer of bark that, like leaves, regulates material exchange at the interface of air, water, and biota. Through interception, retention, and leaching of materials and interactions with epiphytic communities, bark alters the chemistry and composition of water draining over its surface during precipitation. This mini-review explores different perspectives and approaches to the study of bark and what they reveal about the myriad ways bark surfaces influence the quality of sub-canopy precipitation. Observational studies conducted over the past five decades in the fields of environmental science, ecohydrology, epiphyte ecology, and microbiology demonstrate that bark is an accumulator, transporter, substrate, and reactor. Bark passively accumulates materials from the atmosphere, water, and canopies, and also serves as an active transport surface, exchanging materials laterally and longitudinally. In addition, bark substrates influence epiphyte diversity, composition, and distribution, which, in turn, affect material cycling. Bark surfaces are dynamic over time, changing in response to disturbances (e.g., insect outbreaks, aging, and tree death)—how such changes influence the chemical and elemental composition of throughfall and stemflow merits further study. Moving forward, integration of diverse perspectives and approaches is needed to elucidate the influence of bark surfaces on solute and particulate transport and cycling within woody ecosystems.

Modeling the Flow and Transport Dynamics in Gasoline Particulate Filters to Improve Filtration Efficiency

We propose a new pore-scale/channel model, or hybrid model, for the fluid flow and particulate transport in gasoline particulate filters (GPFs). GPFs are emission control devices aimed at removing particulate out of the exhaust system of a gasoline direct injection engine. In this study, we consider a wall-flow uncoated GPF, which is made of a bundle of inlet and outlet channels separated by porous walls. The particulate-filled exhaust gas flows into the inlet channels, and passes through the porous walls before exiting out of the outlet channels. We model the flow inside the inlet and outlet channels using the incompressible Navier–Stokes equation coupled with the spatially averaged Navier–Stokes equation for the flow inside the porous walls. For the particulate transport, the coupled advection and spatially averaged advection–reaction equations are used, where the reaction term models the particulate accumulation. Using OpenFOAM, we numerically solve the flow and the transport equations and show that the concentration of deposited particles is nonuniformly distributed along the filter length, with an increase of concentration at the back end of the filter as Reynolds number increases. Images from X-ray computed tomography (XCT)-scanning experiments of the soot-loaded filter show that such a nonuniform distribution is consistent with the prediction obtained from the model. Finally, we show how the proposed model can be employed to optimize the filter design to improve filtration efficiency.

Modeling the Transport Dynamics in Gasoline Particulate Filters

We develop the flow and the particulate transport models in a wall-flow gasoline particulate filter (GPF). The filter is constituted of inlet channels which are separated from outlet channels by a porous wall. We model the flow inside the channel using incompressible Navier-Stokes equation coupled with the spatially averaged Navier-Stoke equation for the porous wall. For the particulate transport, we use coupled advection and spatially averaged advection-reaction equations, where the reaction term models the particles trapping. The concentration of deposited particulates at the back of the filter downstream the flow increases with Reynolds number. These results are in agreement with the published experimental measurements of the spatial distribution of particles inside the filter.