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1 Dynamic, Absolute and Kinematic Viscosity An introduction to dynamic, absolute and kinematic viscosity and how to convert between CentiStokes (cst), CentiPoises (cp), Saybolt Universal Seconds (SSU), degree Engler and more Search Custom Search Sponsored Links The viscosity of a fluid is an important property in the analysis of liquid behavior and fluid motion near solid boundaries. The viscosity is the fluid resistance to shear or flow and is a measure of the adhesive/cohesive or frictional fluid property. The resistance is caused by intermolecular friction exerted when layers of fluids attempt to slide by one another. Viscosity is a measure of a fluid's resistance to flow The knowledge of viscosity is needed for proper design of required temperatures for storage, pumping or injection of fluids. There are two related measures of fluid viscosity - known as dynamic (or absolute) and kinematic viscosity. Dynamic (absolute) Viscosity Absolute viscosity or the coefficient of absolute viscosity is a measure of the internal resistance. Dynamic (absolute) viscosity is the tangential force per unit area required to move one horizontal plane with respect to the other at unit velocity when maintained a unit distance apart by the fluid. The shearing stress between the layers of non turbulent fluid moving in straight parallel lines can be defined for a Newtonian fluid as: 1 of :47

2 The dynamic or absolute viscosity can be expressed like τ = μ dc/dy (1) τ = shearing stress μ = dynamic viscosity Equation (1) is known as the Newtons Law of Friction. In the SI system the dynamic viscosity units are N s/m 2, Pa.s or kg/m.s 1 Pa.s = 1 N s/m 2 = 1 kg/m.s The dynamic viscosity is also often expressed in the metric CGS (centimeter-gram-second) system as g/cm.s, dyne.s/cm 2 or poise (p) 1 poise = dyne s/cm 2 = g/cm.s = 1/10 Pa.s = 1/10 N.s/m 2 For practical use the Poise is to large and it's usual divided by 100 into the smaller unit called the centipoise (cp) 1 p = 100 cp 1 cp = 0.01 poise = 0.01 gram per cm second = Pascal second = N.s/m 2 Water at 68.4 o F (20.2 o C) has an absolute viscosity of one centipoise. Liquid Absolute Viscosity at Room Temperature (Pa.s) Air 1 x 10-5 Water 1 x 10-3 Olive Oil 1 x 10-1 Glycerol 1 x 10 0 Liquid Honey 1 x 10 1 Golden Syrup 1 x 10 2 Glass 1 x Absolute or Dynamic Viscosity of some common Liquids 2 of :47

3 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 it's mass density ν = μ / ρ (2) ν = kinematic viscosity μ = absolute or dynamic viscosity ρ = density In the SI-system the theoretical unit is m 2 /s or commonly used Stoke (St) 1 St = 10-4 m 2 /s Since the Stoke is an unpractical large unit, it is usual divided by 100 to give the unit called Centistokes (cst) 1 St = 100 cst 1 cst = 10-6 m 2 /s Since the specific gravity of water at 68.4 o F (20.2 o C) is almost one (1), the kinematic viscosity of water at 68.4 o F is for all practical purposes 1.0 cst. Kinematic Viscosities of Some common Liquids and Fluids Conversion from absolute to kinematic viscosity can also be expressed as: ν = μ / γ (2a) ν = kinematic viscosity (ft 2 /s) μ = absolute or dynamic viscosity (cp) γ = specific weight (lb/ft 3 ) Viscosity and Reference Temperatures The viscosity of a fluid is highly temperature dependent and for either 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 will decrease with higher temperature For a gas - the kinematic viscosity will increase with higher temperature Related Mobile Apps from The Engineering ToolBox Kinematic Viscosity Converter App - free apps for offline use on mobile devices. Other Commonly used Viscosity Units Saybolt Universal Seconds (or SUS, SSU) Saybolt Universal Seconds (or SUS) is used to measure 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 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 versus dynamic or absolute viscosity can be expressed as 3 of :47

4 ν = 4.63 μ / SG (3) ν = kinematic vicosity (SSU) μ = dynamic or absolute viscosity (cp) SG = Specific Gravity 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 a 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 centimetres 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 o C or 100 o C) in a standardized Engler viscosity meter. Newtonian Fluids Fluids for which the shearing stress is linearly related to the rate of shearing strain are designated as Newtonian Fluids. Newtonian materials are referred to as true liquids since their viscosity or consistency is not affected by shear such as agitation or pumping at a constant temperature. Fortunately most common fluids, both liquids and gases, are Newtonian. Water and oils are examples of Newtonian liquids. Shear-thinning or Pseudoplastic Liquids Shear-thinning or pseudoplastic liquids are those whose viscosity decreases with increasing shear rate. Their structure is time-independent. Thixotropic Fluids Thixotropic liquids have a time-dependent structure. The viscosity of a thixotropic liquid 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 Shear Thickening Fluids or Dilatant Fluids increase their viscosity with agitation. Some of these liquids can become almost solid within a pump or pipe line. With agitation, cream becomes butter and Candy compounds, clay slurries and similar heavily filled liquids do the same thing. Bingham Plastic Fluids Bingham Plastic Fluids have a yield value which must be exceeded before it will start to flow like a fluid. From that point the viscosity will decrease with increase of agitation. Toothpaste, mayonnaise and tomato catsup are examples of such products. Example - Converting between Kinematic and Absolute Viscosity for Air Kinematic viscosity of air at 1 bar (10 5 Pa, N/m 2 ) and 40 o C is cst ( m 2 /s). The density of air estimated with the Ideal Gas Law ρ = p / R T ρ = density (kg/m 3 ) p = absolute pressure (Pa, N/m 2 ) R = individual gas constant (J/kg.K) T = absolute temperature (K) ρ = 10 5 (N/m 2 ) / (287 (J/kg/K) (273 ( o C) + 33 ( o C)) 4 of :47

5 = (kg/m 3 ) Absolute viscosity can be expressed as μ = (kg/m 3 ) (m 2 /s) = (kg/m s, N.s/m 2, P) Viscosity of some Common Liquids centistokes (cst) Saybolt Second Universal (SSU, SUS) Typical liquid 1 31 Water (20 o C) Milk SAE 20 Crankcase Oil SAE 75 Gear Oil No. 4 fuel oil Cream Vegetable oil SAE 30 Crankcase Oil SAE 85 Gear Oil Tomato Juice SAE 50 Crankcase Oil SAE 90 Gear Oil SAE 140 Gear Oil Glycerine (20 o C) SAE 250 Gear Oil ,000 Honey ,000 Mayonnaise 19,000 86,000 Sour cream Kinematic viscosity can be converted from SSU to Centistokes like ν Centistokes = ν SSU / ν SSU ν SSU < 100 ν Centistokes = ν SSU / ν SSU ν SSU > 100 Viscosity and Temperature Kinematic viscosity of liquids like water, mercury, oils SAE 10 and oil no. 3 - and gases like air, hydrogen and helium are indicated below. Note that for liquids viscosity decreases with temperature for gases viscosity increases with temperature 5 of :47

6 Viscosity Measurements Three types of devices are used in viscosity measurements capillary tube viscometer Saybolt viscometer rotatiting viscometer Sponsored Links Search the Engineering Toolbox Custom Search Search 6 of :47

7 Share +6 Share this on Google+ Tweet Recommend 54 Related Topics Fluid Flow and Pressure Drop - 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. Involves various properties of the fluid, such as velocity, pressure, density and temperature, as functions of space and time. Material Properties - Material properties - density, heat capacity, viscosity and more - for gases, fluids and solids Pumps - Piping systems and pumps - centrifugal pumps, displacement pumps - cavitation, viscosity, head and pressure, power consumption and more Related Documents Absolute or Dynamic Viscosity Online Converter - Convert between dynamic or absolute viscosity units - Poiseuille, Poise, centpoise and more Air - Absolute and Kinematic Viscosity - Absolute and kinematic viscosity of air at temperatures ranging o C ( o F) at standard atmospheric pressure - Imperial and SI Units Air Properties - Temperature, density, specific heat, thermal conductivity, expansion coefficient, kinematic viscosity and Prandtl's number for temperatures ranging o C Centrifugal Pumps and Viscosity - When a liquid flow through a pump, hydrodynamic losses depends on fluid viscosity Comparing Secondary Coolants - Specific gravity, freezing points and viscosity for secondary coolants like calcium chloride, sodium chloride, ethylene glycol and propylene glycol Dynamic Viscosity of Motor Oils - SAE 10 to 50 - temperature ranging 0-10 deg C Dynamic Viscosity of some common Liquids - Absolute or Dynamic Viscosity viscosity of some common fluids Dynamic or Absolute Viscosity Converting Chart - Absolute or dynamic viscosity converting chart - units like Poiseuille - Poise - centipoise and more Fluids - Kinematic Viscosities - Kinematic viscosities of some common fluids - motor oil, diesel fuel, peanut oil and many more Friction Loss Viscous Liquids - Friction loss in steel pipes - viscosities ranging SSU Friction Loss Viscous Liquids - Friction loss in schedule 40 steel pipe with viscous liquids with viscosity from water to 1500 SSU Fuel Oils - Viscosities - Fuels oils - their viscosity versus temperature Heat Emission from Pipes Submerged in Oil or Fat - Heat emission from steam or water heating pipes submerged in oil or fat - assisted (forced) and natural circulation ISO Grade Oil Properties - Viscosity and density of ISO Grade oil Industrial Lubricants - Viscosity ISO-VG Grade - ISO-VG viscosity grades for industrial lubricants International Standard Atmosphere - International standard atmosphere - ranging elevation to meters - pressure, temperature, density, viscosity, thermal conductivity and velocity of sound Kinematic Conversion Diagram - Convert diagram between Centistokes, Saybolt and Redwood seconds Kinematic Viscosity Online Calculator - Convert between different kinematic viscosity units - centistokes, poise, lentor and more Major loss in Ducts, Tubes and Pipes - Major loss - head loss or pressure loss - due to friction in ducts, pipes and tubes 7 of :47

8 Oil Viscosity Conversion Values - Convert between common oil viscosity units Pressure Drop in Oil Pipes - Pressure drop in oil pipes - viscosity ranging Saybolt Universal Seconds Recommended Delivery Flow Velocity of Viscous Liquids - Normal flow velocities on the delivery side of the pump in viscous systems Reynolds Number - An introduction and definition of the dimensionless Reynolds Number - with online calculators SAE Multigrade Oil Properties - Viscosity and density of SAE Grade oil Steam Viscosity - Steam absolute viscosity at pressures ranging psia Viscosity Converting Chart - A converting table between viscosity units like Centiposes, millipascal, CentiStokes and SSU Viscosity of Foods - Absolute or dynamic viscosity of some common foods Viscous Fluids - Recommended Suction Flow Velocity - Recommended suction flow velocity of viscous fluids Water - Absolute or Dynamic Viscosity - Absolute, or dynamic viscosity of water in centipoises for temperatures between o F Water - Dynamic and Kinematic Viscosity - Viscosity of water at temperatures between o C ( o F) - in Imperial and SI Units Williams Hazens Equation of Pressure Drop - The Hazen-Williams equation can be used to calculate pressure drop (psi) in pipes or tubes due to friction Sponsored Links ToolBox Tools 3D Engineering ToolBox - 3D modelling of technical applications with Google SketchUp! 2D Engineering ToolBox - create and share online diagram drawings with Google Docs! Engineering ToolBox Apps - mobile online and offline engineering applications! Disclaimers The content in The Engineering ToolBox is COPYRIGHTED but can be used with NO WARRANTY or LIABILITY Important information should always be double checked with alternative sources. All applicable national and local regulations and practices concerning this aspects must be strictly followed and adhered to. 8 of :47

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Dynamic (absolute) Viscosity

Dynamic (absolute) Viscosity Viscosity Taken from: http://www.engineeringtoolbox.com/dynamic-absolute-kinematic-viscosity-d_412.html The viscosity of a fluid is an important property in the analysis of liquid behavior and fluid motion