What is the Viscometer？
About Viscometer
A viscometer is an instrument used to measure the flow and viscosity of a liquid. The viscosity of a liquid affects how it behaves during pumping, piping, dipping and coating.
Measuring viscosity is therefore useful for a wide variety of materials, including:Petroleum 、Plastics 、Paints 、Coatings、 Adhesives 、Waxes
Measuring viscosity and flow properties is also useful in the production of common consumer products such as food, beverages, toothpaste, cosmetics and shampoo.
What does a viscometer do?
Viscometers are used to measure the viscosity and flow characteristics of liquids and have a wide range of applications where they can measure these characteristics across different substances and materials.
Examples of these applications include:
*Monitoring the viscosity of jams and syrups during the production of food condiments to ensure consistency across batches
*Analyzing the flow characteristics when designing piping systems for milk
*Measuring the flow of motor oil at different temperatures
*Testing the viscosity of inkjet printer inks
Viscosity is important in the lubrication of machines. If the viscosity is too low, there will be too much contact between internal components, causing wear. If the viscosity is too high, the oil will force the machine to work harder to overcome the internal resistance of the oil itself to flow.
What is viscosity?
Viscosity is a measure of how well a material resists movement when a force is applied to it.
For example, if you squeeze a tube of toothpaste, how easily does the paste come out of the end of the tube?There is a formula for measuring viscosity:Viscosity = Shear stress / Shear rate.
You will express the result of this formula in centipoise (cP). A centipoise is equivalent to 1 millipascal second.This is for absolute viscosity. For kinematic viscosity, the measurement is different, which we will explain in more detail later.Shear stress is the force per unit area required to move one layer of fluid relative to another.Shear rate is a measure of how fast the layers change as they move relative to each other.
For many liquids, the stress that causes flow is proportional to the rate of change of shear strain. For a particular fluid, at a particular temperature, the value of shear stress divided by shear rate is constant.This constant is the dynamic viscosity or absolute viscosity. But you can also simply call it the viscosity of a material.A simple way to look at viscosity is to think of it as the thickness of a fluid, but when you look at fluids of varying densities, the clearest way to describe viscosity is as resistance to flow.
Why is measuring viscosity so important?
The processing conditions of a material are critical both in the production of the material and in its end use.
The viscosity of a material is also a useful indirect measure of its properties, such as molecular weight and density. These material properties affect its flow characteristics.
Measuring viscosity is an important task in quality control and batch consistency.
Measuring viscosity is also important because not all fluids behave the same way.
Broadly speaking, there are two main types:
*Newtonian, and
*Non-Newtonian.
Newtonian refers to Newton's law of viscosity, which is the accepted formula for measuring viscosity. In a Newtonian fluid, the viscosity is constant and does not change with changes in shear rate.Typical examples of Newtonian fluids are water and motor oil.
However, in a non-Newtonian fluid, the viscosity changes. These fluids include the following types:
1.Plastics
2.Pseudoplastics
3.Rheological thickening
4.Thixotropy
5.Dilatant
A common example of a non-Newtonian fluid is ketchup, which becomes thinner when you shake the bottle. Ketchup is shear-thinning because its viscosity decreases as shear stress increases.Kinematic and Absolute Viscosity.There are two ways to express viscosity:
*“Kinematic”
*“Absolute”
You measure the dynamic viscosity of a fluid by looking at its resistance to flow under the force of gravity.You determine its absolute viscosity by measuring the resistance of a liquid to flow under the force of an external, controllable force.The two viscosities are also measured differently.The unit for kinematic viscosity is centistokes (CSt).The unit for absolute viscosity is centipoise (cP).
What Kinds of Viscometer Are There?
There are two basic methods for measuring viscosity:Either an object passes through a stationary material, or material flows through or past a stationary object.With either method, you record the time it takes for the operation to happen, which measures the resistance to flow.
Using either of these two methods, there are various kinds of viscometer:
*Capillary, or glass, viscometer
*Rotational viscometer
*Falling ball and falling piston viscometer.
*Viscometers measure Newtonian viscosity.
There are also rheometers for measuring non-Newtonian viscosity, and which do this using multiple parameters.
How Do You Choose a Viscometer?
As we have seen, there is a broad range of applications for viscometers and rheometers.
*What factors should you consider when choosing an instrument for measuring viscosity?
*What type of viscosity will you need to measure for, absolute, kinematic, or both?
*Where will you conduct your work, in a laboratory setting, on the move, or elsewhere?
*How complex or varied will the materials be that you want to measure?
Generally, rheometers are more versatile, and more expensive, instruments than viscometers, but rheometers will measure non-Newtonian fluids.
When it comes to types of viscometers and rheometers, there are various broad instrument categories, covering:
*Portable, handheld viscometers
*Glass capillary viscometers
*Rotational viscometers
*Ball bearing and air bearing rheometers.
Conclusion
Viscometers are indispensable for quantifying flow resistance in liquids, impacting industries from food to aerospace. Choosing between viscometers (simpler, cost-effective) and rheometers (advanced, versatile) depends on fluid behavior and precision needs. Temperature control and density corrections are critical for accurate measurements.