Constant viscosity elastic fluid (original) (raw)
In der Rheologie zählen Boger-Fluide zu den nichtnewtonschen Fluiden, da sie eine messbare erste Normalspannung besitzen. Wie newtonsche Fluide weisen sie aber eine von der Scherrate unabhängige Viskosität auf.
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| dbo:abstract | In der Rheologie zählen Boger-Fluide zu den nichtnewtonschen Fluiden, da sie eine messbare erste Normalspannung besitzen. Wie newtonsche Fluide weisen sie aber eine von der Scherrate unabhängige Viskosität auf. Boger-Fluide können in Form hochverdünnter Polymerlösungen realisiert werden, bei denen die für Polymerlösungen und -schmelzen typische Scherverdünnung vernachlässigbar ist. Die werden bei Scherung des Fluids in Richtung der Scherung gestreckt. Wird der Fluss gestoppt, so relaxieren die Polymerketten wieder zu einer (im Mittel) isotropen Knäuelgestalt. Diese Konformationsänderung der gelösten Polymerketten bewirkt makroskopisch ein elastisches Zurückfedern des Fluids. (de) Constant viscosity elastic liquids, also known as Boger fluids are elastic fluids with constant viscosity. This creates an effect in the fluid where it flows like a liquid, yet behaves like an elastic solid when stretched out. Most elastic fluids exhibit shear thinning (viscosity decreases as shear strain is applied), because they are solutions containing polymers. But Boger fluids are exceptions since they are highly dilute solutions, so dilute that shear thinning caused by the polymers can be ignored. Boger fluids are made primarily by adding a small amount of polymer to a Newtonian fluid with a high viscosity, a typical solution being polyacrylamide mixed with corn syrup. It is a simple compound to synthesize but important to the study of rheology because elastic effects and shear effects can be clearly distinguished in experiments using Boger fluids. Without Boger fluids, it was difficult to determine if a non-Newtonian effect was caused by elasticity, shear thinning, or both; non-Newtonian flow caused by elasticity was rarely identifiable. Since Boger fluids can have constant viscosity, an experiment can be done where the results of the flow rates of a Boger liquid and a Newtonian liquid with the same viscosity can be compared, and the difference in the flow rates would show the change caused by the elasticity of the Boger liquid. (en) |
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| rdfs:comment | In der Rheologie zählen Boger-Fluide zu den nichtnewtonschen Fluiden, da sie eine messbare erste Normalspannung besitzen. Wie newtonsche Fluide weisen sie aber eine von der Scherrate unabhängige Viskosität auf. (de) Constant viscosity elastic liquids, also known as Boger fluids are elastic fluids with constant viscosity. This creates an effect in the fluid where it flows like a liquid, yet behaves like an elastic solid when stretched out. Most elastic fluids exhibit shear thinning (viscosity decreases as shear strain is applied), because they are solutions containing polymers. But Boger fluids are exceptions since they are highly dilute solutions, so dilute that shear thinning caused by the polymers can be ignored. Boger fluids are made primarily by adding a small amount of polymer to a Newtonian fluid with a high viscosity, a typical solution being polyacrylamide mixed with corn syrup. It is a simple compound to synthesize but important to the study of rheology because elastic effects and shear effec (en) |
| rdfs:label | Boger-Fluid (de) Constant viscosity elastic fluid (en) |
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