| Autor: |
Schymura, S., Kulenkampff, J., Franke, K., Lippmann-Pipke, J. |
| Jazyk: |
angličtina |
| Rok vydání: |
2017 |
| Předmět: |
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| Zdroj: |
Interpore 2017, 08.-11.05.2017, Rotterdam, Netherlands |
| Popis: |
The retention of particles in porous media is typically attributed to filtrtation effects such as straning, adsorption, or sedimentation. However, using positron emission tomography (PET) as imaging modality we were able to show the effect of hindrance in concentrated nanofluids due to particle-particle interactions. A flow-through column experiment with a MWCNT nanofluid was devised for optimal particle mobility: strong repulsive interactions between particles and between particles and the matrix (glass beads), inhibiting aggregation and adsorption and a large pore size rendering straining unlikely. Using the PET technique we could observe the transport of the MWCNT nanofluid through the glass bead packing in situ. During pulse injection of the suspension into the porous media the suspension spread out as a horizontal plume at the bottom of the column by “flooding” the respective pore volume. After this pulse injection the subsequently injected water seemed to penetrate the suspension only mobilizing MWCNTs from the top of the suspension plume rather than displacing the bulk of injected nanofluid. This mobilization from the top of the plume is most effective in the central parts of the column where the flow velocity is highest while most of the nanofluid is trapped in more stagnant zones of the pore space at the bottom edges of the column with minimal MWCNT displacement. The mobilized MWCNTs are higly diluted and only visible via the continuous diminishing of the plume from its central top boundry. These observations can be explained by a pronounced hindrance of the particle transport due to particle-particle interactions in the concentrated suspension (Lamas et al, 2012) which is only overcome at the edges of the nanofluid plume, primarily in the central zones of highest flow velocity. Controlled sedimentation experiments reveal the absence of settling for high MWCNT concentrations due to hindrance. This hindrance which inhibits gravitational settling in turn also inhibits transport, in particular at low flow velocities. In order to achieve the PET measurements the MWCNTs used in this experiment were oxidzed by oxidative acid treatment and radiolabeled with the positron emitter I-125. In an uncomplicated one-pot synthesis the CNTs were labeled by an electrophilic attack of I+ on the electron-rich CNT side-wall catalyzed by the so-called iodogen 1,3,4,6-Tetrachloro-3α-6α-diphenylglucoluril. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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