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The
measurement of rheological properties can help to
develop a better product, predict its end use performance
with customers and predict the physical properties
of a product during and after processing.
Rheology
is defined as the flow of fluids and deformation
of solids under stress and strain. Rheometers are
the instruments used to measure a material’s rheological
properties. There are many types of rheometers that
are available with the most versatile being controlled
stress and/or strain rheometers and capillary rheometers.
Whether
your objective is to simply measure viscosity as
a function of shear rate to determine non-Newtonian
flow behavior, or whether you want to measure complex
rheological properties such as viscoelasticity (G’,
G”) as a function of frequency (time) or temperature,
our F-273VR system will help you to solve rheological
applications in a wide variety of industries.
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An
important mechanical property of fluids is viscosity.
Physical systems and applications as diverse as
fluid flow in pipes, the flow of blood, lubrication
of engine parts, the dynamics of raindrops, volcanic
eruptions, planetary and stellar magnetic field
generation, to name just a few, all involve fluid
flow and are controlled to some degree by fluid
viscosity. Viscosity is defined as the internal
friction of a fluid. The microscopic nature of internal
friction in a fluid is analogous to the macroscopic
concept of mechanical friction in the system of
an object moving on a stationary planar surface.
Energy must be supplied to overcome the inertial
state of the interlocked object and plane caused
by surface roughness, and to initiate and sustain
motion of the object over the plane. In a fluid,
energy must be supplied to create viscous flow units
by breaking bonds between atoms and molecules, and
to cause the flow units to move relative to one
another. The resistance of a fluid to the creation
and motion of flow units is due to the viscosity
of the fluid, which only manifests itself when motion
in the fluid is set up. Since viscosity involves
the transport of mass with a certain velocity, the
viscous response is called a momentum transport
process. The velocity of flow units within the fluid
will vary, depending on location. Consider a liquid
between two closely spaced parallel plates. A force,
F, applied to the top plate causes the fluid adjacent
to the upper plate to be dragged in the direction
of F. The applied force is communicated to neighboring
layers of fluid below, each coupled to the driving
layer above, but with diminishing magnitude. This
results in the progressive decrease in velocity
of each fluid layer away from the upper plate. In
this system, the applied force is called a shear
(when applied over an area it is called a shear
stress), and the resulting deformation rate of the
fluid is called the shear strain rate.
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