The effect of adsorbed liquid and material density on saltation threshold: Insight from laboratory and wind tunnel experiments

Xinting Yu, Sarah M. Hörst, Chao He, Nathan T. Bridges, Devon M. Burr, Joshua A. Sebree, James Smith

Research output: Contribution to journalArticle

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Abstract

Saltation threshold, the minimum wind speed for sediment transport, is a fundamental parameter in aeolian processes. Measuring this threshold using boundary layer wind tunnels, in which particles are mobilized by flowing air, for a subset of different planetary conditions can inform our understanding of physical processes of sediment transport. The presence of liquid, such as water on Earth or methane on Titan, may affect the threshold values to a great extent. Sediment density is also crucial for determining threshold values. Here we provide quantitative data on density and water content of common wind tunnel materials (including chromite, basalt, quartz sand, beach sand, glass beads, gas chromatograph packing materials, walnut shells, iced tea powder, activated charcoal, instant coffee, and glass bubbles) that have been used to study conditions on Earth, Titan, Mars, and Venus. The measured density values for low density materials are higher compared to literature values (e.g., ∼30% for walnut shells), whereas for the high density materials, there is no such discrepancy. We also find that low density materials have much higher water content and longer atmospheric equilibration timescales compared to high density sediments. We used thermogravimetric analysis (TGA) to quantify surface and internal water and found that over 80% of the total water content is surface water for low density materials. In the Titan Wind Tunnel (TWT), where Reynolds number conditions similar to those on Titan can be achieved, we performed threshold experiments with the standard walnut shells (125–150 µm, 7.2% water by mass) and dried walnut shells, in which the water content was reduced to 1.7%. The threshold results for the two scenarios are almost the same, which indicates that humidity had a negligible effect on threshold for walnut shells in this experimental regime. When the water content is lower than 11.0%, the interparticle forces are dominated by adsorption forces, whereas at higher values the interparticle forces are dominated by much larger capillary forces. For materials with low equilibrium water content, like quartz sand, capillary forces dominate. When the interparticle forces are dominated by adsorption forces, the threshold does not increase with increasing relative humidity (RH) or water content. Only when the interparticle forces are dominated by capillary forces does the threshold start to increase with increasing RH/water content. Since tholins have a low methane content (0.3% at saturation, [Curtis, D. B., Hatch, C. D., Hasenkopf, C. A., et al., 2008. Laboratory studies of methane and ethane adsorption and nucleation onto organic particles: Application to Titan's clouds. Icarus, 195, 792. http://dx.doi.org/10.1016/j.icarus.2008.02.003]), we believe tholins would behave similarly to quartz sand when subjected to methane moisture.

Original languageEnglish (US)
Pages (from-to)97-109
Number of pages13
JournalIcarus
Volume297
DOIs
StatePublished - Nov 15 2017

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saltation
wind tunnels
wind tunnel
tunnels
moisture content
water content
Titan
liquid
thresholds
liquids
low density materials
shell
sands
experiment
methane
sand
humidity
sediment transport
quartz
adsorption

Keywords

  • Aeolian processes
  • Experimental techniques
  • Surface
  • Titan

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

The effect of adsorbed liquid and material density on saltation threshold : Insight from laboratory and wind tunnel experiments. / Yu, Xinting; Hörst, Sarah M.; He, Chao; Bridges, Nathan T.; Burr, Devon M.; Sebree, Joshua A.; Smith, James.

In: Icarus, Vol. 297, 15.11.2017, p. 97-109.

Research output: Contribution to journalArticle

Yu, Xinting ; Hörst, Sarah M. ; He, Chao ; Bridges, Nathan T. ; Burr, Devon M. ; Sebree, Joshua A. ; Smith, James. / The effect of adsorbed liquid and material density on saltation threshold : Insight from laboratory and wind tunnel experiments. In: Icarus. 2017 ; Vol. 297. pp. 97-109.
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AU - He, Chao

AU - Bridges, Nathan T.

AU - Burr, Devon M.

AU - Sebree, Joshua A.

AU - Smith, James

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N2 - Saltation threshold, the minimum wind speed for sediment transport, is a fundamental parameter in aeolian processes. Measuring this threshold using boundary layer wind tunnels, in which particles are mobilized by flowing air, for a subset of different planetary conditions can inform our understanding of physical processes of sediment transport. The presence of liquid, such as water on Earth or methane on Titan, may affect the threshold values to a great extent. Sediment density is also crucial for determining threshold values. Here we provide quantitative data on density and water content of common wind tunnel materials (including chromite, basalt, quartz sand, beach sand, glass beads, gas chromatograph packing materials, walnut shells, iced tea powder, activated charcoal, instant coffee, and glass bubbles) that have been used to study conditions on Earth, Titan, Mars, and Venus. The measured density values for low density materials are higher compared to literature values (e.g., ∼30% for walnut shells), whereas for the high density materials, there is no such discrepancy. We also find that low density materials have much higher water content and longer atmospheric equilibration timescales compared to high density sediments. We used thermogravimetric analysis (TGA) to quantify surface and internal water and found that over 80% of the total water content is surface water for low density materials. In the Titan Wind Tunnel (TWT), where Reynolds number conditions similar to those on Titan can be achieved, we performed threshold experiments with the standard walnut shells (125–150 µm, 7.2% water by mass) and dried walnut shells, in which the water content was reduced to 1.7%. The threshold results for the two scenarios are almost the same, which indicates that humidity had a negligible effect on threshold for walnut shells in this experimental regime. When the water content is lower than 11.0%, the interparticle forces are dominated by adsorption forces, whereas at higher values the interparticle forces are dominated by much larger capillary forces. For materials with low equilibrium water content, like quartz sand, capillary forces dominate. When the interparticle forces are dominated by adsorption forces, the threshold does not increase with increasing relative humidity (RH) or water content. Only when the interparticle forces are dominated by capillary forces does the threshold start to increase with increasing RH/water content. Since tholins have a low methane content (0.3% at saturation, [Curtis, D. B., Hatch, C. D., Hasenkopf, C. A., et al., 2008. Laboratory studies of methane and ethane adsorption and nucleation onto organic particles: Application to Titan's clouds. Icarus, 195, 792. http://dx.doi.org/10.1016/j.icarus.2008.02.003]), we believe tholins would behave similarly to quartz sand when subjected to methane moisture.

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