Dynamic vs Kinematic Viscosities: What’s the Difference?

When we want to assess a fluid’s resistance to flow, we express it in a scientific term called ‘viscosity’. It is also defined as the fluid’s ability to resist deformity when subjected to a force. As a primal element of every fluid material, finding out viscosity using the correct viscometer is critical to studying the fluid flow for any application. 

Since the viscosity of a fluid is our primary focus, it’s important to know that there are two types of viscosity – dynamic and kinematic and the relationship between these two is fairly simple and uncomplicated.

Understanding the Difference Between Dynamic Viscosity & Kinematic Viscosities

Also called absolute viscosity, dynamic viscosity is the evaluation of the internal resistance of the fluid to flow. On the contrary, kinematic viscosity explains the ratio of dynamic viscosity to density. On the basis of this expression, two liquids with the same dynamic viscosities can have different kinematic viscosities, considering the density. And the reverse can happen too. Therefore, understanding the real meaning of the two types of viscosities may not always be so straightforward. 

In simple terms, dynamic viscosity enables you to know the force required to make the fluid flow at a specific rate while kinematic viscosity helps to understand how fast the fluid is moving under the influence of force. 

Measuring Dynamic Viscosity

Usually, dynamic viscosity is measured using an NDJ digital viscometer. The equipment has a probe that is rotated in the test fluid. Viscosity is found out by measuring the torque or force required to turn the probe. 

Although they can measure the viscosity of Newtonian fluids, NDJ viscometers are particularly used for assessing the viscosity of non-Newtonian liquids as well. For instance, the NDJ-8S digital viscometer comes with a high-performing microcomputer chip, step motor and other advanced components. It has a rotor spec of #1, #2, #3, and #4 and a measuring range of 1～2,000,000S. 

It is important to know that there’s a change in the viscosity of non-Newtonian fluids when exposed to various conditions. For instance, the viscosity of some liquids increases with the increase in applied force while for certain non-Newtonian fluids, the viscosity decreases when there’s an increase in applied force. 

Centipoise (cP) is the unit for measuring dynamic viscosity

Measuring Kinematic Viscosity

The kinematic viscosity of any fluid can be found out in multiple ways. However, the most popular way is determining the time taken for the fluid to flow into a capillary tube. Utilizing a calibration constant that is provided for the particular tube, the measured time is directly converted to kinematic viscosity.

Centistokes (cSt) is the unit for measuring kinematic viscosity 

Did You Know?

Density is the prime differentiating factor between dynamic and kinematic viscosities. The density of the fluid actually offers a method to convert into a kinematic or dynamic viscosity measurement. 

Get High-Precision Digital Viscometers for Measuring Dynamic & Kinematic Viscosities

One of the features of Newtonian fluids is that their viscosity doesn’t get altered at the change of the force applied to the fluids. This type of viscosity can be accurately and easily measured using a capillary-type viscometer in which the liquid moves with the force of gravity. 

On the contrary, non-Newtonian fluids display major variations in viscosity depending on the applied force. To measure such viscosities, you need NDJ viscometers that are capable of measuring variations over a diverse range of applied forces. 

If you’re searching for a reliable manufacturer who can supply a suitable viscometer to measure dynamic or kinematic viscosities or both, feel free to contact Viscorun. The ISO 9001 certified company is distinguished for manufacturing DV, NDJ and SNB viscometers for varied industrial uses.