The viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress. For liquids, it corresponds to the informal notion of "thickness". A liquid whose viscosity is less than that of water is sometimes known as a mobile liquid, while a substance with a viscosity substantially greater than water is called a viscous liquid.
The dynamic (shear) viscosity of a fluid expresses its resistance to shearing flows, where adjacent layers move parallel to each other with different speeds
The SI physical unit of dynamic viscosity is the pascal-second (Pa·s), (equivalent to (N·s)/m2, or kg/(m·s)). Water at 20°C has a viscosity of 0.001002 Pa·s, while a typical motor oil could have a viscosity of about 0.250 Pa·s.
The cgs physical unit for dynamic viscosity is the poise. It is more commonly expressed, particularly in ASTM standards, as centipoise (cP). Water at 20°C has a viscosity of 1.0020 cP.
Rotational viscometers use the idea that the torque required to turn an object in a fluid is a function of the viscosity of that fluid. They measure the torque required to rotate a disk or bob in a fluid at a known speed.
- Viscosity measurements are very useful in the food, cosmetics, oils and fuels industry and more.It is important for manufacturers that the flow of material remains the same.Manufacturers test the viscosity of the raw materials and their products during production and of course of the final product.
There are several methods for measuring viscosity:
Kinematic measurement: By measuring the flow time in glass piping at a certain temperature. (Useful in the fuel industry)
Measurement with a viscometer - by testing the torque (resistance force) required to maintain a constant rotational speed.
Viscosity of fluids with variable compositions:
Viscosity of liquids: (at 25 °C unless otherwise specified)
MRC represents "Fungilab" in its products viscosity .
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