Extensional viscosity (also known as elongational viscosity) is a
viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the int ...
coefficient when applied
stress
Stress may refer to:
Science and medicine
* Stress (biology), an organism's response to a stressor such as an environmental condition
* Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...
is
extensional stress. It is often used for characterizing polymer solutions.
Extensional viscosity can be measured using rheometers that apply ''extensional stress''.
Acoustic rheometer
An acoustic rheometer employs a piezo-electric crystal that can easily launch a successive wave of extensions and contractions into the fluid. It applies an oscillating extensional stress to the system. System response can be interpreted in ter ...
is one example of such devices.
Extensional viscosity is defined as the ratio of the normal stress difference to the rate of strain. For uniaxial extension along direction
:
[Guyon, E., Hulin, JP. and Petit, L., Physical Hydrodynamics, Oxford University Press (2015), p113]
:
where
:
is the extensional viscosity or elongational viscosity
:
is the normal
stress
Stress may refer to:
Science and medicine
* Stress (biology), an organism's response to a stressor such as an environmental condition
* Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...
along direction n.
:
is the rate of strain:
The ratio between the extensional viscosity
and the
dynamic viscosity is known as
Trouton's Ratio . For a
Newtonian Fluid, the Trouton ratio equals three.
See also
*
Rheology
Rheology (; ) is the study of the flow of matter, primarily in a fluid ( liquid or gas) state, but also as "soft solids" or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an ap ...
References
Fluid dynamics
Viscosity
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