What is Viscosity?

What is viscosity?

Viscosity is a measure of a substance's resistance to motion under an applied force. 

The formula for measuring viscosity is very simple:

Viscosity = shear stress / shear rate

Results are usually expressed in centipoise (cP), equivalent to 1 mPa s (milliPascal second). 

Shear stress is the force per unit area required to move one layer of fluid relative to another.

Shear rate is a measure of the change in speed at which the interlayers move relative to each other.

Newtonian and non-Newtonian fluids

Isaac Newton, the man who discovered this formula, believed that at a given temperature and shear stress, the viscosity of the fluid would remain constant regardless of changes in the shear rate. 

He's only partially right. Some liquids, such as water and honey, do behave this way. We call these fluids Newtonian fluids. However, the viscosity of most fluids fluctuates with shear rate. These are called non-Newtonian fluids.

There are five types of non-Newtonian fluids: thixotropic, rheological, pseudoplastic, dilatant, and plastic. There are different factors to consider when measuring these fluid types.

Who does the viscosity test?

Here is an example of how to use viscosity measurement:

FOOD

Viscosity measurement is used in the food industry to maximize production efficiency and cost-effectiveness. It affects how quickly the product moves through the tube, how long it takes to set or dry, and how long it takes the fluid to dispense into the pack. The production process needs to take into account the viscosity of the product, making sure that the pipe is sloped to optimize flow, or that the dispenser provides just the right amount of force to direct the flow, but not so much that the package will overflow.

Viscosity is also characteristic of food texture. The viscosity of the product needs to be measured and monitored during the production process to ensure that each batch of product is consistent and completes the process efficiently. 

adhesive

To choose the proper viscosity for your adhesive, consider how the adhesive needs to flow or not flow after it has been applied. Low-viscosity adhesives flow more easily than high-viscosity adhesives, so if you want your adhesive to stay exactly where you put it after dispensing—rather than spreading out—high-viscosity adhesives are a good choice. 

other industry

Petroleum: Viscosity measurements predict the effectiveness of lubricating oils and determine design factors for pipelines.

Concrete: Viscosity determines the self-leveling and pumping behavior of the mixture.

Cosmetics: Viscosity should be considered when designing the feel and flow of cosmetics.