# Viscosity - Absolute (Dynamic) vs. Kinematic

Viscosity is an important fluid property when analyzing liquid behavior and fluid motion near solid boundaries. The viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress. The shear resistance in a fluid is caused by inter-molecular friction exerted when layers of fluid attempt to slide by one another.

*viscosity is the measure of a fluid's resistance to flow*

- molasses is highly viscous
- water is medium viscous
- gas is low viscous

There are two related measures of fluid viscosity

**dynamic**(**or absolute**)**kinematic**

### Dynamic (absolute) Viscosity

Absolute viscosity - coefficient of absolute viscosity - is a measure of internal resistance. Dynamic (absolute) viscosity is the tangential force per unit area required to move one horizontal plane with respect to an other plane - at an unit velocity - when maintaining an unit distance apart in the fluid.

The shearing stress between the layers of a non turbulent fluid moving in straight parallel lines can be defined for a Newtonian fluid as

**Shear stress **can be expressed

τ = μ dc / dy

=μ γ(1)

where

τ = shearing stress in fluid (N/m^{2})

μ = dynamic viscosity of fluid (N s/m^{2})

dc = unit velocity (m/s)

dy = unit distance between layers (m)

= dc / dy = shear rate (sγ^{-1})

Equation *(1)* is known as the **Newtons Law of Friction.**

*(1)* can be rearranged to express **Dynamic viscosity** as

*μ* = *τ dy / dc *

* = τ / γ (1b)*

In the SI system the dynamic viscosity units are * N s/m^{2}, Pa s or kg/(m s)* - where

*1 Pa s = 1 N s/m*^{2}= 1 kg/(m s) = 0.67197 lb_{m}/(ft s)*= 0.67197 slug/(ft s) = 0.02089 lb*_{f }s/ft^{2}

Dynamic viscosity may also be expressed in the metric *CGS (centimeter-gram-second)* system as * g/(cm s), dyne s/cm^{2}* or

*where*

**poise (p)***1 poise = 1 dyne s/cm*^{2}= 1 g/(cm s) = 1/10 Pa s = 1/10 N s/m^{2}

For practical use the *Poise* is normally too large and the unit is therefore often divided by *100* - into the smaller unit * centipoise (cP)* - where

*1 P = 100 cP**1 cP = 0.01 poise = 0.01 gram per cm second = 0.001 Pascal second**= 1 milliPascal second*= 0.001 N s/m^{2}

Water at * 20.2^{o}C (68.4^{o}F) *has the absolute viscosity of

*one*-

*1 - centiPoise*.

Liquid | Absolute Viscosity ^{*)}(N s/m, Pa s)^{2} |
---|---|

Air | 1.983 10^{-5} |

Water | 10^{-3} |

Olive Oil | 10^{-1} |

Glycerol | 10^{0} |

Liquid Honey | 10^{1} |

Golden Syrup | 10^{2} |

Glass | 10^{40} |

*) at room temperature

### Kinematic Viscosity

Kinematic viscosity is the ratio of *- absolute (or dynamic) viscosity to density* - a quantity in which no force is involved. Kinematic viscosity can be obtained by dividing the absolute viscosity of a fluid with the fluid mass density like

ν = μ / ρ (2)

where

ν = kinematic viscosity (m^{2}/s)

μ = absolute or dynamic viscosity (N s/m^{2})

ρ = density (kg/m^{3})

In the SI-system the theoretical unit of kinematic viscosity is *m ^{2}/s* - or the commonly used

*where*

**Stoke (St)**

*1 St (Stokes) = 10*^{-4}m^{2}/s = 1 cm^{2}/s

Stoke comes from the CGS (Centimetre Gram Second) unit system.

Since the *Stoke* is a large unit it is often divided by *100* into the smaller unit * centiStoke (cSt)* - where

*1 St = 100 cSt**1 cSt (centiStoke) = 10*^{-6}m^{2}/s = 1 mm^{2}/s*1 m*^{2}/s = 10^{6}centiStokes

The specific gravity for water at* 20.2^{o}C (68.4^{o}F) *is almost

*one,*and the kinematic viscosity for water at

*is for practical purpose*

*20.2*(68.4^{o}C^{o}F)*1.0*A more exact kinematic viscosity for water at

*mm*cStokes).^{2}/s (*is*

*20.2*(68.4^{o}C^{o}F)*1.0038 mm*

^{2}/s (cSt).A conversion from absolute to kinematic viscosity in Imperial units can be expressed as

ν = 6.7197 10^{-4}μ / γ (2a)

where

ν = kinematic viscosity (ft^{2}/s)

μ = absolute or dynamic viscosity (cP)

γ= specific weight (lb/ft^{3})

### Viscosity and Reference Temperature

The viscosity of a fluid is highly temperature dependent - and for dynamic or kinematic viscosity to be meaningful the **reference temperature** must be quoted. In ISO 8217 the reference temperature for a residual fluid is *100 ^{o}C*. For a distillate fluid the reference temperature is

*40*.

^{o}C- for a liquid - the kinematic viscosity
**decreases**with higher temperature - for a gas - the kinematic viscosity
**increases**with higher temperature

### Related Mobile Apps from The Engineering ToolBox

This is a free app that can be used offline on mobile devices.

### Other Viscosity Units

#### Saybolt Universal Seconds (or *SUS, SSU*)

Saybolt Universal Seconds (or *SUS*) is an alternative unit for measuring viscosity. The efflux time is Saybolt Universal Seconds (*SUS*) required for 60 milliliters of a petroleum product to flow through the calibrated orifice of a Saybolt Universal viscometer - under a carefully controlled temperature and as prescribed by test method ASTM D 88. This method has largely been replaced by the kinematic viscosity method. Saybolt Universal Seconds is also called the *SSU number (Seconds Saybolt Universal)* or *SSF number (Saybolt Seconds Furol)*.

Kinematic viscosity in SSU versus dynamic or absolute viscosity can be expressed as

ν_{SSU}= B μ / SG

= Bν_{centiStokes}(3)

where

ν_{SSU}= kinematic viscosity (SSU)

B = 4.632 for temperature100^{o}F (37.8^{o}C)

B = 4.664 for temperature210^{o}F (98.9^{o}C)μ = dynamic or absolute viscosity (cP)

SG = Specific Gravity

= kinematic viscosity (centiStokes)ν_{centiStokes}

#### Degree Engler

*Degree Engler* is used in Great Britain as a scale to measure kinematic viscosity. Unlike the *Saybolt* and *Redwood* scales, the *Engler* scale is based on comparing the flow of the substance being tested to the flow of another substance - water. Viscosity in *Engler* degrees is the ratio of the time of a flow of *200 cubic centimeters* of the fluid whose viscosity is being measured - to the time of flow of *200 cubic centimeters* of water at the same temperature (usually *20 ^{o}C* but sometimes

*50*) in a standardized

^{o}C or 100^{o}C*Engler*viscosity meter.

### Newtonian Fluids

A fluid where the shearing stress is linearly related to the rate of shearing strain - is designated as a **Newtonian Fluid.**

A Newtonian material is referred to as true liquid since the viscosity or consistency is not affected by shear such as agitation or pumping at a constant temperature. Most common fluids - both liquids and gases - are Newtonian fluids. Water and oils are examples of Newtonian liquids.

**Shear-thinning or ****Pseudo-plastic Fluids**

A Shear-thinning or pseudo-plastic fluid is a fluid where the viscosity decrease with increased shear rate. The structure is time-independent.

### Thixotropic Fluids

A Thixotropic fluid has a time-dependent structure. The viscosity of a thixotropic fluid decreases with increasing time - at a constant shear rate.

Ketchup and mayonnaise are examples of thixotropic materials. They appear thick or viscous but are possible to pump quite easily.

### Dilatant Fluids

A Shear Thickening Fluid - or Dilatant Fluid - increases the viscosity with agitation or shear strain. Dilatant fluids are known as non-Newton fluids.

Some dilatant fluids can become almost solid in a pump or pipe line. With agitation cream becomes butter and candy compounds. Clay slurry and similar heavily filled liquids do the same thing.

### Bingham Plastic Fluids

A Bingham Plastic Fluid has a yield value which must be exceeded before it will start to flow like a fluid. From that point the viscosity decreases with increasing agitation. Toothpaste, mayonnaise and tomato ketchup are examples of such products.

### Example - Air, Convert between Kinematic and Absolute Viscosity

Kinematic viscosity of air at *1 bar (1 10 ^{5} Pa, N/m^{2})* and

*40*is

^{o}C*16.97 cSt (16.97 10*.

^{-6}m^{2}/s)The density of the air can be estimated with the Ideal Gas Law

ρ = p / (R T)

= (1 10^{5}N/m^{2}) / ( (287 J/(kg K)) ((273^{o}C) + (33^{o}C)) )

= 1.113 (kg/m^{3})

where

ρ = density (kg/m^{3})

p = absolute pressure (Pa, N/m^{2})

R = individual gas constant (J/(kg K))

T = absolute temperature (K)

The absolute viscosity can be calculated as

μ = 1.113 (kg/m^{3}) 16.97 10^{-6 }(m^{2}/s)

= 1.88 10^{-5}(kg/(m s), N s/m^{2})

### Viscosity of some Common Liquids

centiStokes(cSt, )10^{-6} m^{2}/s, mm^{2}/s | Saybolt Second Universal (SSU, SUS) | Typical liquid |
---|---|---|

0.1 | Mercury | |

1 | 31 | Water (20^{o}C) |

4.3 | 40 | Milk SAE 20 Crankcase Oil SAE 75 Gear Oil |

15.7 | 80 | No. 4 fuel oil |

20.6 | 100 | Cream |

43.2 | 200 | Vegetable oil |

110 | 500 | SAE 30 Crankcase Oil SAE 85 Gear Oil |

220 | 1000 | Tomato Juice SAE 50 Crankcase Oil SAE 90 Gear Oil |

440 | 2000 | SAE 140 Gear Oil |

1100 | 5000 | Glycerine (20^{o}C)SAE 250 Gear Oil |

2200 | 10000 | Honey |

6250 | 28000 | Mayonnaise |

19000 | 86000 | Sour cream |

Kinematic viscosity can be converted from *SSU* to *Centistokes* with

ν_{Centistokes}= 0.226ν_{SSU}- 195 /ν_{SSU }(4)_{}

where

ν_{SSU}< 100

ν_{Centistokes}= 0.220ν_{SSU}- 135 /ν_{SSU}

where

ν_{SSU}> 100

### Viscosity and Temperature

Kinematic viscosity of fluids like water, mercury, oils SAE 10 and oil no. 3 - and gases like air, hydrogen and helium are indicated in the diagram below. Note that

- for liquids - viscosity
**decreases**with temperature - for gases - viscosity
**increases**with temperature

### Measuring Viscosity

Three types of devices are used to measure viscosity

- capillary tube viscometer
- Saybolt viscometer
- rotating viscometer

## Related Topics

### • Fluid Flow and Pressure Loss

Pipe lines - fluid flow and pressure loss - water, sewer, steel pipes, pvc pipes, copper tubes and more.

### • Fluid Mechanics

The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.

### • Material Properties

Material properties of gases, fluids and solids - densities, specific heats, viscosities and more.

### • Pumps

Piping systems and pumps - centrifugal pumps, displacement pumps - cavitation, viscosity, head and pressure, power consumption and more.

### • Viscosities

Viscosities of products and chemical species at varying conditions.

## Related Documents

### Absolute or Dynamic Viscosity Online Converter

Convert between dynamic or absolute viscosity units - Poiseuille, Poise, centPoise and more.

### Acetone - Thermophysical Properties

Chemical, physical and thermal properties of acetone, also called 2-propanone, dimethyl ketone and pyroacetic acid. Phase diagram included.

### Air - Dynamic and Kinematic Viscosity

Online calculator, figures and tables with dynamic (absolute) and kinematic viscosity for air at temperatures ranging -100 to 1600°C (-150 to 2900°F) and at pressures ranging 1 to 10 000 bara (14.5 - 145000 psia) - SI and Imperial Units.

### Air - Thermophysical Properties

Thermal properties of air at different temperatures - density, viscosity, critical temperature and pressure, triple point, enthalpi and entropi, thermal conductivity and diffusivity and more.

### Ammonia - Dynamic and Kinematic Viscosity vs. Temperature and Pressure

Online calculator, figures and tables showing dynamic (absolute) and kinematic viscosity of gasous and liquid ammonia at temperatures ranging from -73 to 425°C (-100 to 800°F) at pressure ranging from 1 to 1000 bara (14.5 - 14500 psia) - SI and Imperial Units.

### Ammonia - Prandtl Number vs. Temperature and Pressure

Figures and table with changes in Prandtl number for ammonia with changes in temperature and pressure.

### Benzene - Dynamic and Kinematic Viscosity vs. Temperature and Pressure

Online calculator, figures and table showing dynamic and kinematic viscosity of benzene, C_{6}H_{6}, at varying temperature and pressure - Imperial and SI Units.

### Benzene - Thermophysical properties

Chemical, physical and thermal properties of benzene, also called benzol. Phase diagram included.

### Butane - Dynamic and Kinematic Viscosity vs. Temperature and Pressure

Online calculators, figures and tables with dynamic and kinematic viscosity of liquid and gaseous butane, C_{4}H_{10}, at varying temperarure and pressure, SI and Imperial units.

### Centrifugal Pumps - Viscosity Influence

Hydrodynamic losses through pumps depends on fluid viscosities.

### Crude Oil Viscosity vs. Gravity

Viscosity at 20°C/68°F and 50°C/122°F for more than 120 crudes is shown as function of specific gravity@15°C/60°F.

### Dynamic (Absolute) Viscosity - Converting Chart

Convert dynamic viscosity values between units like *Poiseuille - Poise - centiPoise* and more.

### Energy Equation - Pressure Loss vs. Head Loss

Calculate pressure loss - or head loss - in ducts, pipes or tubes.

### Engine & Gear Oil - Recommended Viscosity vs. Outside Temperature

Oil viscosity vs. temperature.

### Ethanol - Dynamic and Kinematic Viscosity vs. Temperature and Pressure

Online calculator, figures and tables showing dynamic and kinematic viscosity of ethanol, C_{2}H_{5}OH, at varying temperature and pressure - Imperial and SI Units.

### Ethylene - Dynamic and Kinematic Viscosity vs. Temperature and Pressure

Online calculator, figures and tables showing dynamic and kinematic viscosity of ethylene, C_{2}H_{4}, also called ethene or acetene, at varying temperature and pressure - Imperial and SI Units.

### Ethylene - Thermophysical Properties

Chemical, physical and thermal properties of ethylene, also called ethene, acetene and olefiant gas. Phase diagram included.

### Food Products - Viscosities

Absolute (dynamic) viscosity for common food products.

### Gases - Dynamic Viscosities

Absolute (dynamic) viscosities of some common gases.

### Hazen-Williams Pressure Loss Equation

The Hazen-Williams equation can be used to calculate the pressure drop (psi) or friction loss in pipes or tubes.

### Heavy Water - Thermophysical Properties

Thermodynamic properties of heavy water (D_{2}O) like density, melting temperature, boiling temperature, latent heat of fusion, latent heat of evaporation, critical temperature and more.

### Industrial Lubricants - Viscosities vs. ISO-VG Grade

ISO-VG viscosity grades for industrial lubricants.

### International Standard Atmosphere

International standard atmosphere in elevation *-2000 to 30000 metre* - pressure, temperature, density, viscosity, thermal conductivity and velocity of sound.

### ISO Grade Oils - Viscosities and Densities

Viscosities and densities of ISO - and equivalent SAE grade oils.

### Kinematic Viscosity - Convert between Units

Convert between Centistokes, Saybolt and Redwood seconds.

### Kinematic Viscosity - Online Converter

Convert between kinematic viscosity units like centistokes, poise, lentor and more.

### Liquids - Dynamic Viscosities

Absolute (dynamic) viscosity values for some common fluids.

### Liquids - Kinematic Viscosities

Kinematic viscosities of some common liquids like motor oil, diesel fuel, peanut oil and many more.

### Methane - Dynamic and Kinematic Viscosity vs. Temperature and Pressure

Online calculator, figures and tables showing dynamic and kinematic viscosity of methane, CH_{4}, at varying temperature and pressure - Imperial and SI Units.

### Methane - Prandtl number vs. Temperature

Figures and table showing changes in Prandtl number for methane with changes in temperature and pressure.

### Methanol - Dynamic and Kinematic Viscosity vs. Temperature and Pressure

Online calculator, figures and tables showing dynamic and kinematic viscosity of liquid methanol,CH_{3}OH, at varying temperature - Imperial and SI Units.

### Motor Oils - Dynamic Viscosities

Dynamic viscosities for motor oils SAE 10 to 50 for temperatures ranging 0-100 ^{o}C.

### Nitrogen - Prandtl number vs. Temperature and Pressure

Figures and tables showing Prandtl number of nitrogen at varying temperarure and pressure, SI and Imperial units.

### Oil Fuels - Viscosities vs. Temperature

Viscosities of fuel oils vs. temperature.

### Oil Pipes - Pressure Loss vs. Oil Flow

Pressure drop in oil pipes - viscosities ranging *100 - 600 Saybolt Universal Seconds*.

### Oil Viscosity Converter

Convert between commonly used oil viscosity units.

### Oxygen - Dynamic and Kinematic Viscosity vs. Temperature and Pressure

Online calculator, figures and tables showing dynamic and kinematic viscosity of oxygen, O_{2}, at varying temperature and pressure - Imperial and SI Units.

### Pipes Submerged in Oil or Fat - Heat Emission

Heat emission from steam or water heating pipes submerged in oil or fat - forced and natural circulation.

### Poiseuille's Formula

Calculate the volume flow discharged through a smooth-walled circular pipe.

### Propane - Dynamic and Kinematic Viscosity vs. Temperature and Pressure

Online calculators, figures and tables showing dynamic and kinematic viscosity of liquid and gaseous propane at varying temperarure and pressure, SI and Imperial units.

### Propane - Prandtl Number vs. Temperature and Pressure

Figures and tables with Prandtl Number of liquid and gaseous propane at varying temperarure and pressure, SI and Imperial units.

### Reynolds Number

Introduction and definition of the dimensionless Reynolds Number - online calculators.

### SAE Multigrade Oils - Viscosities and Densities

Viscosities and densities of SAE Grade oils.

### Seawater - Properties

Seawater properties like density, saturation pressure, specific heat, electrical conductivity and absolute viscosity.

### Secondary Coolants - Properties

Comparing properties like specific gravity, freezing points and viscosity for secondary coolants like calcium chloride, sodium chloride, ethylene glycol and propylene glycol.

### Steam - Viscosity vs. Pressure

Absolute viscosity of steam at pressure ranging *1 - 10000 psia*.

### Steel Pipes - Friction Loss vs. Viscous Liquid Flow

Friction loss in schedule 40 steel pipe with viscous liquids - viscosities ranging from water to oil.

### Sugar Water Solutions - Viscosities

Dynamic viscosities of sucrose water solutions vs. temperature.

### Viscosity - Converter Chart

Convert between viscosity units like *Centiposes, milliPascal, CentiStokes and SSU*.

### Viscous Liquids - Friction Loss vs. Viscosity and Flow

Friction loss in steel pipes for fluids with viscosities ranging *32 - 80000 SSU*.

### Viscous Liquids - Max. Delivery Flow Velocities

Recommended max. flow velocities on delivery sides of pumps in viscous systems.

### Viscous Liquids - Max. Suction Flow Velocities

Recommended max. pump suction flow velocity for viscous fluids.

### Water - Absolute (Dynamic) Viscosity vs. Temperature and Pressure

Absolute viscosity for water in centipoises for temperatures between *32 - 200 ^{o}F*.

### Water - Dynamic (Absolute) and Kinematic Viscosity vs. Temperature and Pressure

Free online calculator - figures and tables with viscosity of water at temperatures ranging 0 to 360°C (32 to 675°F) - Imperial and SI Units.