Are standard values the best choice? A critical statement on rheological soil fluid properties viscosity and surface tension

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  • University of Göttingen
  • Kiel University
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Original languageEnglish
Pages (from-to)61-71
Number of pages11
JournalSoil and Tillage Research
Volume125
Publication statusPublished - Sept 2012
Externally publishedYes

Abstract

The rheological properties of a fluid in terms of viscosity η and surface tension γ are often neglected in studies on hydrostatic and hydrodynamic phenomena. However, their measurement seems to provide us with more benefit than it takes time and effort. Especially regarding transport of fluids in soil, the exact definition of the fluid properties is necessary for predicting water transport correctly.In this paper we review and summarize the available scientific knowledge on rheological soil fluid properties and supplement it with our own investigations on viscosity and surface tension of salt and soil solutions. Our results showed neither a clear linear relationship between η and salt concentration in aqueous solutions nor to the kind of cation or anion of the dissolved salt whereas the surface tension of salt solutions generally increased linearly with molar concentration though at different rates. As an example, a 1M MgSO4 solution doubled η but increased γ only by 3%, whereas 1M MgCl2 caused 4% increase in γ, but still 50% increase in η. Viscosity of soil solutions depended on soil-water ratio as well as fertilization of the soil. The largest deviation to standard η of water was about 6% at 40% gravimetric water content.Concluding from the literature review and our own findings, we recommend to additionally measure rheology (namely viscosity and surface tension) of the soil solution in order to improve modeling of hydrostatic and hydrodynamic phenomena in soils by utilizing more realistic fluid properties which might deviate significantly from the usually employed standard values. The mathematical error cumulates with increasing salt concentration as a deviation of 10% to the standard value also causes an error of 10% in linear relationships derived from that parameter, e.g. the equation of Hagen-Poiseuille.Future investigations should focus on the manifold single effects as well as on the interactions of different dissolved components in the soil solution on viscosity and surface tension and how these are influenced by temperature, pressure (i.e. shear rate) and concentration.

Keywords

    Coupled processes, Fluid and solid mechanics, Rheology of soil solution, Surface tension, Viscosity

ASJC Scopus subject areas

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Are standard values the best choice? A critical statement on rheological soil fluid properties viscosity and surface tension. / Holthusen, D.; Haas, C.; Peth, S. et al.
In: Soil and Tillage Research, Vol. 125, 09.2012, p. 61-71.

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title = "Are standard values the best choice? A critical statement on rheological soil fluid properties viscosity and surface tension",
abstract = "The rheological properties of a fluid in terms of viscosity η and surface tension γ are often neglected in studies on hydrostatic and hydrodynamic phenomena. However, their measurement seems to provide us with more benefit than it takes time and effort. Especially regarding transport of fluids in soil, the exact definition of the fluid properties is necessary for predicting water transport correctly.In this paper we review and summarize the available scientific knowledge on rheological soil fluid properties and supplement it with our own investigations on viscosity and surface tension of salt and soil solutions. Our results showed neither a clear linear relationship between η and salt concentration in aqueous solutions nor to the kind of cation or anion of the dissolved salt whereas the surface tension of salt solutions generally increased linearly with molar concentration though at different rates. As an example, a 1M MgSO4 solution doubled η but increased γ only by 3%, whereas 1M MgCl2 caused 4% increase in γ, but still 50% increase in η. Viscosity of soil solutions depended on soil-water ratio as well as fertilization of the soil. The largest deviation to standard η of water was about 6% at 40% gravimetric water content.Concluding from the literature review and our own findings, we recommend to additionally measure rheology (namely viscosity and surface tension) of the soil solution in order to improve modeling of hydrostatic and hydrodynamic phenomena in soils by utilizing more realistic fluid properties which might deviate significantly from the usually employed standard values. The mathematical error cumulates with increasing salt concentration as a deviation of 10% to the standard value also causes an error of 10% in linear relationships derived from that parameter, e.g. the equation of Hagen-Poiseuille.Future investigations should focus on the manifold single effects as well as on the interactions of different dissolved components in the soil solution on viscosity and surface tension and how these are influenced by temperature, pressure (i.e. shear rate) and concentration.",
keywords = "Coupled processes, Fluid and solid mechanics, Rheology of soil solution, Surface tension, Viscosity",
author = "D. Holthusen and C. Haas and S. Peth and R. Horn",
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T1 - Are standard values the best choice? A critical statement on rheological soil fluid properties viscosity and surface tension

AU - Holthusen, D.

AU - Haas, C.

AU - Peth, S.

AU - Horn, R.

N1 - Funding Information: The first author is grateful to the K+S KALI GmbH (Kassel, Germany) for financial support and to the reviewer for valuable comments.

PY - 2012/9

Y1 - 2012/9

N2 - The rheological properties of a fluid in terms of viscosity η and surface tension γ are often neglected in studies on hydrostatic and hydrodynamic phenomena. However, their measurement seems to provide us with more benefit than it takes time and effort. Especially regarding transport of fluids in soil, the exact definition of the fluid properties is necessary for predicting water transport correctly.In this paper we review and summarize the available scientific knowledge on rheological soil fluid properties and supplement it with our own investigations on viscosity and surface tension of salt and soil solutions. Our results showed neither a clear linear relationship between η and salt concentration in aqueous solutions nor to the kind of cation or anion of the dissolved salt whereas the surface tension of salt solutions generally increased linearly with molar concentration though at different rates. As an example, a 1M MgSO4 solution doubled η but increased γ only by 3%, whereas 1M MgCl2 caused 4% increase in γ, but still 50% increase in η. Viscosity of soil solutions depended on soil-water ratio as well as fertilization of the soil. The largest deviation to standard η of water was about 6% at 40% gravimetric water content.Concluding from the literature review and our own findings, we recommend to additionally measure rheology (namely viscosity and surface tension) of the soil solution in order to improve modeling of hydrostatic and hydrodynamic phenomena in soils by utilizing more realistic fluid properties which might deviate significantly from the usually employed standard values. The mathematical error cumulates with increasing salt concentration as a deviation of 10% to the standard value also causes an error of 10% in linear relationships derived from that parameter, e.g. the equation of Hagen-Poiseuille.Future investigations should focus on the manifold single effects as well as on the interactions of different dissolved components in the soil solution on viscosity and surface tension and how these are influenced by temperature, pressure (i.e. shear rate) and concentration.

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