#### What is kinematic viscosity?

The **kinematic **viscosity [m^{2}/s] is the ratio between the **dynamic **viscosity [Pa.s = 1 kg/m·s] and the density of a fluid [kg/m^{3}].

The SI unit of the **kinematic **viscosity is m^{2}/s. Other units are: 1 St (*Stoke*) = 1 cm^{2}/s = 10^{−4} m^{2}/s. 1 cSt (*centiStoke*) = 1 mm^{2}/s = 10^{−6}m^{2}/s.

Water at 20 °C has a **kinematic **viscosity of about 1 cSt.

One way is to measure a fluid’s resistance to flow when an external force is applied. This is **dynamic viscosity**.

__The other way is to measure the resistive flow of a fluid under the weight of gravity. The result is kinematic viscosity. __

__Put 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.__

## Measuring Kinematic Viscosity** **

There are several ways to find the kinematic viscosity of a fluid, but the most common method is determining the time it takes a fluid to flow through a capillary tube. The time is converted directly to kinematic viscosity using a calibration constant provided for the specific tube.

## The unit of measure of kinematic viscosity is Centistokes (cSt).

A basic difference between the dynamic and kinematic viscosity measurements is density.

Density actually provides a way to convert between a kinematic and a dynamic viscosity measurement. The formula for the conversion is:

- Kinematic (cSt) x Density = Dynamic (cP)
- Dynamic (cP) / Density = Kinematic (cSt)

For a given sample, with a density greater than one, dynamic viscosity will always be the higher number.

## Need a Refresher on Density?

**Density** is the ratio of the mass (or weight) of the sample divided by the volume of the sample. Think about an ice cube and a cube of steel. They may be the same size, but the steel cube weighs more than the ice cube. Therefore, we say that steel has a greater density than ice cube.

The mass (or weight) of a fluid is determined by gravity. In the kinematic measuring method, gravity is the only force that acts on the sample.

## Different viscosities for Vortex Flow Meters

The LIQUI-VIEW Base series operate on the vortex principle.

The obstruction (bluff body) placed in the flow of the liquid sheds vortices downstream at a frequency proportional to the velocity of the liquid.

A piezoelectric sensor detects the vortices and creates electrical pulses which are proportional to the liquid flow rate.

LIQUI-VIEW Base provides the output either with **pulse output** or **analog output (4-20 mA)**.

The LIQUI-VIEW instruments are able to work up to 1.8 cSt with an accuracy of <2%RD

With a viscosity of 1.8 - 4cSt the measuring accuracy is 3%FS, between 4 - 14 cSt the accuracy will be around 4% FS.

Liquid | Kinematic Viscosity (cSt) |
---|---|

Water | 1 |

Honey | 2000-10000 |

Blood | 2-9 |

Olive oil | 30-60 |

Mayonnaise | 6250-28000 |

* Viscosity changes with temperature, cSt above is average viscosity