Extensional viscosity
Extensional viscosity (also known as elongational viscosity) is a viscosity coefficient when applied stress is extensional stress.[1]
- This parameter is often used for characterizing polymer solutions.
Extensional viscosity can be measured using rheometers that apply extensional stress. Acoustic rheometer is one example of such devices.
\[\eta_e = \frac{\sigma_n}{\dot{\varepsilon}}\,\!\]
where
\[\eta_e\,\!\] is the extensional viscosity or elongational viscosity \[\sigma_n\,\!\] is the normal stress\[\sigma_n = \frac{F}{A}\,\!\] \[\dot{\varepsilon}\,\!\] is the rate of strain\[\dot{\varepsilon} = \frac{1}{L}\frac{dL}{dt}\,\!\]
For a Newtonian Fluid, the elongational viscosity is three times the shear viscosity which can be derived using the continuity equation for incompressible fluids.
\[\eta_e = 3\eta\,\!\]
References
- ↑ Barnes, H.A. "A handbook of elementary rheology", Institute of non-Newtonian Fluid Mechanics, 2000
See also
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