Distinguish between dynamic viscosity and kinematic viscosity
Answers
dynamic viscosity is to measure a fluid’s resistance to flow when an external force is applied.
kinematic viscosityis to measure the resistive flow of a fluid under the weight of gravity. In another way, kinematic viscosity is the measure of a fluid’s inherent resistance to flow when no external force, except gravity, is acting on it.
i am giving some more information regarding this. i hope it may be useful.
When Should You Use Dynamic Viscosity Measurements?
You test dynamic viscosity when you want to know the internal resistance of a fluid, or the force required to move one plane of the liquid over another.
The measurement of dynamic viscosity is most useful for liquids which change their apparent characteristics as force or pressure is applied. These liquids are known as non-Newtonian fluids. Non-Newtonian fluids are sensitive to changes in the amount of force exerted on them, and can sometimes even permanently change their viscosity if a constant force has been has been exerted on them over a period of time.
An example of the importance of dynamic viscosity measurement is to indicate the proper flow characteristics of ketchup. This product needs to have lower viscosity as it flows, to get it out of the bottle, but needs to be thick (or not as inclined to flow) when sitting on the burger. Testing the viscosity of the ketchup at different speeds (equating to different levels of force) will help ensure that the ketchup is behaving as it should.
Another application is in the design of pumping systems. Because the viscosity of non-Newtonian liquids changes with the speed of movement, pressure and pump velocity have serious impact on the specification of proper pumps, pressure and piping size. Testing the product at different speeds will help provide guidelines for the design of the pumping system.
When Should You Use Kinematic Viscosity Measurements?
This measurement is used mostly for Newtonian liquids - liquids that do not change viscosity with changes in applied force (shear rate).
Testing lubricating oils is a significant application. Using this testing method, changes in viscosity at different temperatures and under differing environmental conditions can be determined. With this information, changes in lubricating effectiveness can be evaluated.
Some other products for which the kinematic method is suitable are blood and plasma, paints, polymers, and asphalt.
Viscosity measurement for Newtonian fluids can be accomplished using rotational viscometers (via the conversion formula listed above). However, it is simpler to use capillary-based instruments. In some cases, capillary-based instruments are more accurate for determining kinematic viscosity.
When you need to determine the viscosity characteristics of a liquid which is not exposed to outside physical forces (in other words, when gravity is the only force acting on the liquid), kinematic should be the method of choice.