24 Questions
What is the reciprocal of viscosity in a Newtonian system?
Fluidity (f)
What type of rheometer is required to fully characterize a non-Newtonian system?
Multipoint rheometer
What is the name of the materials that exhibit plastic flow?
Bingham bodies
What is the equation that describes plastic flow?
U = F/G
What is the significance of the yield value in plastic flow?
It is the minimum shear stress required for flow to begin
What is the name of the curve that represents the flow behavior of non-Newtonian systems?
Consistency curve
What is the characteristic of pseudoplastic flow?
Shear thinning
What is the rheological property of suspensions that is affected by particle size and concentration?
Viscosity
What is the characteristic of a Newtonian fluid in terms of its viscosity?
Constant viscosity, regardless of the shear rates applied
What is the main difference between a Newtonian and a Non-Newtonian fluid?
The viscosity of a Non-Newtonian fluid changes with the shear rate, whereas a Newtonian fluid's viscosity remains constant.
What is a rheogram, and what does it represent?
A rheogram is a plot of shear rate (G) as a function of shear stress (F), representing the rheologic properties of a material.
What is the characteristic of a dilatant fluid?
Its viscosity increases with an increase in shear rate
What is plastic flow, and what is its characteristic in terms of yield value?
Plastic flow is a type of Non-Newtonian flow that requires a minimum stress, known as the yield value, to initiate flow.
What is the characteristic of a pseudoplastic fluid?
Its viscosity decreases with an increase in shear rate
What is the significance of the rheological properties of suspensions?
They are important in understanding the behavior of suspensions under various shear rates and stress conditions.
What is the purpose of plotting a viscosity function?
To illustrate the relationship between viscosity and shear rate in a fluid.
What is the potential drawback of processing dilatant materials under conditions of high shear?
They may solidify, overloading and damaging processing equipment.
What concentration of small, deflocculated particles is required for a suspension to exhibit dilatant flow properties?
About 50% or greater
What is the behavior of quicksand when subjected to increased strain rate?
Its resistance to shear decreases, causing it to act more like a liquid than a solid.
What is the term for the time-dependent viscosity of a system?
Thixotropy
What is the term for the breakdown of structure in a shear-thinning system?
Hysteresis loop
What is the behavior of a pseudoplastic system when stress is removed or reduced?
The structure does not reform immediately, resulting in a hysteresis loop.
What is the term for the minimum stress required for a material to flow?
Yield value
What is the behavior of a mixture of cornstarch and water (Oobleck) when subjected to a force?
The cornstarch acts as a solid and resists the force.
Study Notes
Newtonian Liquids
- Named after Sir Isaac Newton, these fluids are the simplest type of fluid.
- Characterized by constant viscosity, regardless of the shear rates applied.
- Shear stress is directly proportional to the shear rate.
- Examples: water and oil.
Non-Newtonian Liquids
- Viscosity changes with the shear rate.
- Fail to follow Newton's equation of flow.
- Examples: colloidal solutions, emulsions, liquid suspensions, and ointments.
- Three general types: Plastic, Pseudoplastic, and Dilatant.
Rheogram
- A plot of shear rate (G) as a function of shear stress (F).
- Also known as consistency curves or flow curves.
- Describes the rheologic properties of a given material.
- The simplest form is produced by Newtonian systems.
- The slope, f, is known as fluidity and is the reciprocal of viscosity, η.
Plastic Flow
- Exhibited by materials known as Bingham bodies.
- Flow curves do not pass through the origin but intersect the shear stress axis at a particular point (yield value).
- A Bingham body requires a certain amount of shear stress (yield value) before it begins to flow.
- The slope of the rheogram is termed the Mobility, and its reciprocal is known as the plastic viscosity, U.
Dilatant Flow
- Exhibited by substances possessing dilatant flow properties, such as suspensions containing a high concentration of small, deflocculated particles.
- Examples: Corn starch and water mixture (oobleck), which acts as a solid and resists force when a force is applied.
Thixotropy
- Viscosity of a system depends on both shear rate and time.
- Non-Newtonian systems can exhibit hysteresis loops, where the down curve is displaced relative to the up curve.
- Examples: plastic and pseudoplastic systems.
Learn about the differences between Newtonian and Non-Newtonian liquids, their characteristics, and examples of each.
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